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Growth and Photosynthetic Responses of Australian Subtropical Rainforest Species to Variable Light Environments: Implica...


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GROWTH AND PHOTOSYNTHETIC RESPONSES OF AUSTRALIAN SUBTROPICAL RAINFOREST SPECIES TO VARIABLE LIGHT ENVIRONMENTS: IMPLICATIONS FOR RESTORATION AND MIXED-SPECIES PLANTATIONS By JEFFREY W. KELLY A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2006

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Copyright 2006 by Jeffrey W. Kelly

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To Harrison Shaw Kelly, Harry Er ik Grass, and Everett Ruess

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iv ACKNOWLEDGMENTS I would like to thank my advisor and co mmittee chair, Dr. Shibu Jose, for his numerous ideas and financial support throughout my research. I would like to express my gratitude to my committee members Dr. Debbie Miller, Dr. Rick Williams, and Dr. Doland Nichols for their gracious assistance a nd valuable insight. I would also like to thank Peter Bligh-Jones for invaluable assist ance during my time in Australia, and thanks go out to Mila Bristow for setting the experiment on the right track. I would like to sincerely th ank my parents for their constant benevolence and support during my academic career. I am fore ver indebted to you both for showing me the wonders of the natural world. I wish to thank Erin Maehr for being such a joy-bringer and wonderful presence in my life. I would also like to thank my good fr iends from Gainesville, Eric Holzmueller, Robin Collins, and Ped Daneshgar, for providing frequent and well needed non-academic pursuits, to counteract the o ccasional academic malaise. Fi nally, I would like to thank some wonderful friends from SLC, Brad La rsen, Jake MacFarlane and Joe and Janica Hayes, for proving that true friendship can su rvive great distances and tumultuous events.

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v TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iv LIST OF TABLES............................................................................................................vii LIST OF FIGURES.........................................................................................................viii ABSTRACT.......................................................................................................................ix CHAPTER 1 INTRODUCTION........................................................................................................1 Ecophysiology..............................................................................................................2 Physiological Response to Light..................................................................................3 Leaf Level..............................................................................................................3 Whole Plant Level.................................................................................................5 Successional Gradient...................................................................................................6 History of Australian Rainforest...................................................................................9 History of Subtropical Rainfo rest in New South Wales.............................................10 Rainforest Characteristics....................................................................................12 Study Species.......................................................................................................13 Objectives and Hypotheses.........................................................................................14 Objective 1...........................................................................................................15 Objective 2...........................................................................................................15 2 GROWTH AND PHOTOSYNTHETIC RESPONSES OF SIX AUSTRALIAN SUBTROPICAL RAINFOREST TREE SPE CIES TO A LIGHT GRADIENT.......16 Introduction.................................................................................................................16 Methods......................................................................................................................21 Study Site.............................................................................................................21 Study Species.......................................................................................................21 Shadehouse Experiment......................................................................................21 Photosynthetic Gas Exchange.............................................................................22 Growth Analysis..................................................................................................23 Nutrient Content..................................................................................................23 Statistical Analysis..............................................................................................24 Results........................................................................................................................ .24

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vi Photosynthetic Response.....................................................................................24 Growth Patterns...................................................................................................25 Discussion...................................................................................................................26 3 POTENTIAL FOR SUBTROPICAL RAINFOREST RESTORATION ON ABANDONED AGRICULTURAL L ANDS IN NEW SOUTH WALES, AUSTRALIA..............................................................................................................38 Introduction.................................................................................................................38 Materials and Methods...............................................................................................40 Study Site.............................................................................................................40 Species.................................................................................................................40 Photosynthetic Gas Exchange.............................................................................41 Nutrient Content..................................................................................................41 Statistical Analysis..............................................................................................42 Results........................................................................................................................ .42 Discussion...................................................................................................................43 4 SUMMARY AND CONCLUSIONS.........................................................................53 APPENDIX NUTRIENT CONCENTRATION...............................................................57 LIST OF REFERENCES...................................................................................................59 BIOGRAPHICAL SKETCH.............................................................................................68

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vii LIST OF TABLES Table page 2-1 Life-history data for the study species.....................................................................31 2-2 Total dry biomass production (g), rela tive growth rate between 0 to 96 days (RGR, mg g-1 d-1), specific leaf area (SLA, cm2 g-1) leaf mass ratio (LMR), stem mass ratio (SMR), root mass ratio (R MR), total stem height (cm), and total stem diameter (mm) shown by the six sp ecies at 96 days of growth under high light (HL%), medium light (M L%), and low light (LL%)...............32 2-3 Leaf-level photosynthetic parameters : Light saturated rate of photosynthesis (Amax, mol CO2 m-2 s-1), apparent quantum yield (Aqe, (mol CO2 m-2 s1)/(mol m-2 s-1)), and light compensa tion point (LCP, mol m-2 s-1) shown by the six species grown under high light (HL 60% full sunlight), medium light (ML 30% full sunlight), and low light (LL 10% full sunlight)..............33 3-1 Life-history data for the study species.....................................................................47 3-2 Leaf-level photosynthetic parameters : Light saturated rate of photosynthesis (Amax, mol CO2 m-2 s-1), apparent quantum yield (Aqe, (mol CO2 m-2 s-1)/(mol m-2 s-1)), and light compensation point (LCP, mol m-2 s-1) shown by the seven species grown under 75% full sunlight....................................................................47 A-1 Total nutrient concentration in leaves of six subtropical rainforest species grown under HL (60%), ML (30%) and LL (10%) full sunlight........................................57 A-2 Total nutrient concentration in leaves of seven subtropical rainforest species grown under 75% full sunlight.................................................................................58

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viii LIST OF FIGURES Figure page 2-1 Relative growth rate (mean (SE)) of seedlings of six Au stralian subtropical rainforest trees, grown at 60%, 30%, and 10% of full sunlight...............................34 2-2 A) Diameter growth in (mm) and B) height growth in (cm) (mean (SE)) of seedlings of six Australian subtropical rainforest trees gr own at 60%, 30%, and 10% full sunlight......................................................................................................35 2-3 Light response curve of photosynthe sis as a function of PPFD for A) Elaeocarpus grandis B) Flindersia schottiana and C) Gmelina leichhardtii grown under three light treatments...........................................................................36 2-4 Light response curve of photosynthe sis as a function of PPFD for A) Flindersia brayleyana B) Heritiera trifoliolatum and C) Cryptocarya erythroxylon grown under three light treatments......................................................................................37 3-1 A) Diameter growth (m) and B) height growth (m) (mean (+/SE)) of seedlings of seven Australian subtropical rainforest trees at 3 years, grown under 75% full sunlight......................................................................................................48 3-2 Stem Volume Index (SVI) (m3) (mean (+/SE)) of seedlings of seven Australian subtropical rainforest trees at 3 years, grown under 75% full sunlight....................49 3-3 Light response curve of photosynthe sis as a function of PPFD for A) Elaeocarpus grandis B) Flindersia schottiana and C) Gmelina leichhardtii grown under 75% full sunlight.................................................................................50 3-4 Light response curve of photosynthe sis as a function of PPFD for A) Flindersia brayleyana and B) Lophostemom confertus grown under 75% full sunlight..........51 3-5 Light response curve of photosynthe sis as a function of PPFD for A) Castanospermum australe and B) Heritiera trifoliolatum grown under 75% full sunlight.....................................................................................................................52

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ix Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science GROWTH AND PHOTOSYNTHETIC RESPONSES OF AUSTRALIAN SUBTROPICAL RAINFOREST SPECIES TO VARIABLE LIGHT ENVIRONMENTS: IMPLICATIONS FOR RESTORATION AND MIXED-SPECIES PLANTATIONS By Jeffrey W. Kelly August 2006 Chair: Shibu Jose Major Department: School of Fo rest Resources and Conservation Growth, biomass distribution, and net photos ynthesis were measured for seedlings of six Australian subtropical ra inforest tree species in a sh adehouse experiment consisting of three artificial light envi ronments (10%, 30%, and 60% full sunlight) in order to determine ecophysiological variability to light environment. A field study utilizing natural light (75% full sunlight) compleme nted the shadehouse experiment. An understanding of growth and phot osynthetic potential of subtropi cal rainforest species in relation to variations in light environment can be useful for determining the sequence of species introductions in rainforest restorati on projects and mixed species plantations. Morphological responses followed the typica l sun shade dichotomy, with early and late secondary species ( Elaeocarpus grandis Flindersia brayleyana Flindersia schottiana and Gmelina leichhardtii ) displaying a higher relative growth rate (RGR) compared to mature stage species ( Cryptocarya erythroxylon and Heritiera trifoliolatum ). Based on the shadehouse study, phy siological responses provided limited evidence of a

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x distinct dichotomy between early and late successional species. E. grandis provided a clear representation of an early successi onal species, with marked increase in Amax in high light and an ability to down regulat e photosynthetic mach inery in low light conditions. The remaining species ( F. brayleyana F. schottiana G. leichhardtii, and H. trifoliolatum ) were better represented as falling al ong a shade-tolerant continuum, with limited ability to adjust physiologically to an increase or decrease in light, maintaining similar Amax across all light environments. Results show that most species belong to a shade-tolerant constituency, with an ability to grow and persist across a wide range of light enviro nments. Growth and photosynthetic performance of most species reached a maximum in 30% to 60% of full sunlight found in shadehouse conditions. A ll species under natural conditions displayed an ability to acclimate to heightened light conditions, reaching their highest Amax in 75% full sunlight. Results indicate that the st udy species offer a wide range of potential planting scenarios and silvicultural options, with ample potential to achieve rapid canopy closure and restoration goals.

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1 CHAPTER 1 INTRODUCTION During the later part of the 1980s, nearly all timber extraction from state owned subtropical and tropical rainforest with in New South Wales and Queensland ceased, corresponding to the inclusion of these forest s for listing on the World Heritage register (Erskine et al. 2005). An impetus for World Heritage listing was the continual removal of timber, on state owned lands, above an annual sustainable level and with limited understanding of the requirements necessary for rainforest regeneration (Baur 1989). Prior to the listing of rainforest remnan ts on the World Heritage register and the subsequent change in rainforest manageme nt, very little rese arch was conducted to determine regeneration or silvicultural strategi es for management of rainforest species. Experiments with growing subtropical and tropica l rainforest timber in plantation settings during the early part of the 1900s showed little promise, as a result of limited information or understanding available concerning the si lvicultural and management requirements for subtropical and tropical Australian rainforest species (Erskine et al. 2005). As the native subtropical and tropical rain forest element met the economic and resource needs of the timber industry for the duration of the 19th century, the necessity to further understanding of the silvicultural and management requirement s of rainforest specie s remained minute. With inclusion of state-owned subtropical and tropical rainforest within New South Wales and Queensland on the World Heritage register the imperative for furthering the knowledge base concerning rainforest species developed. Such a prerogative developed with its basis centered on the continued dema nd for rainforest cabinet timbers (Glengross

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2 and Nichols 2005), the potential of cabinet timbers as plantation species (Cameron and Jermyl 1991; Russel et al. 1993; Herbohn et al 1996) and the position of Australia, as one of the wealthiest nations with rainfore st, to provide an example of sustainable management of the rainforest resource (Ada m 1992). The movement into sustainable management of rainforest timbers carries wi th it some broad necessities for successful implementation, such as understanding the re generation requirements of rainforest species, developing silvicultural methods fo r managing desired species, and acquiring information about the ecophysiolo gical variability of subtropi cal and tropical rainforest species. Ecophysiology Plant ecophysiology is the science of unde rstanding how plants respond to abiotic and biotic factors that affect their grow th and development in a given environment (Larcher 2003). Ecophysiological research as sists in determining how and why species grow well under certain conditions and elucidating the factors that limit their growth such as resource competition for water, light, or nutri ents. This field of research provides an understanding of whole plant functions while also providing insight into forest health particularly through identifying st ressful environments to plant growth. One of the most pertinent facets to forestry, of ecophysiological research, is a determ ination of growth and performance of tree species. In conducti ng ecophysiological research, a prime method for elucidating growth and performance of plant species is to select a suite of environmental variables and evaluate the response of species to the range of environmental variables selected. A major emphasis of ecophysiological research has been the relationship between sunlight a nd plant function, dist ribution, and growth (Chazdon et al. 1996). Sunlight presents a pervasive and omnipresent resource which

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3 distributes copious supplies of energy to terrestrial ecosystems, thereby directly influencing the global distribu tion and general behavior of plant species (Atwell et al. 1999). Physiological Response to Light Light is one of the most integral enviro nmental variables influencing the growth and distribution of plant species (Boardman 1977; Lambers et al. 1998). Growth, performance, and survival of tree seedlings a nd saplings within forested ecosystems are guided by the amount of light available at a given site (Denslow 1980, 1987; Chazdon 1988; Caldwell and Pearcy 1994). Low-light levels may strain plants by limiting photosynthesis, leading to reduced carbon ga in and reduced growth. Conversely, high levels of light can lead to photoinhibition, resulting in damage to the photosynthetic apparatus (Lambers et al. 1998). Under high ra diation loads plant spec ies may also suffer from increased water loss through higher tran spiration rates (Lambers et al. 1998). To account for variability of the li ght environment, species have developed strategies to cope with environmental stresses from changes at the leaf-level through morphological and physiological acclimation to changes at the whol e plant level with adjustments to biomass distribution and crown archit ecture (Kitajima 1994; Sipe and Bazzaz 1994; Poorter 1999; Jose et al. 2003). Leaf Level Acclimation of morphological and physiologi cal traits of seedling foliage has been well documented for both early (light-demanding) and late (shade-tolerant) successional species (Oberhauer and Strain 1984; Pearcy 1987; Strauss-Debendetti and Bazzaz 1991; Turnbull et al. 1993; Kitajima 1994). Early successional (light-demanding) species are found to be more plastic in their response to environmental change than late successional

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4 (shade-tolerant) species (Strauss-Deb endetti and Bazzaz 1991, 1996; Bazzaz 1996). Plasticity or ability to react to a change in the environmen t, of early successional species operates through photosynthetic characteristics and morphological change (Lambers et al. 1998). In most cases, photosynthetic rate per unit leaf area is great er for pioneer, lightdemanding species (Walters et al. 1993; Kitajima 1994; Reich et al. 1995). Moving between light intensities, shade-tolerant species display lower variability in photosynthetic responses when grown under different irradiances than do lightdemanding species (Strauss-Debendetti a nd Bazzaz 1996; Valladares 2000). Limited response by shade-tolerant spec ies reflects an inability to increase electron transport, carboxylation capacity, and stomatal conductance (Chazdon et al. 1996). In contrast, the inherently high photosynthetic capacity of light-demanding species provides a built in mechanism for altering photosynthetic prope rties (Chazdon 1992), exhibited through a down-regulation of electron tr ansport and carboxylation capacity in response to a low light environment (Chazdon et al. 1996). Succe ssional status of trees is also determined by a suite of ecophysiological, morphological and demographi c traits in relation to fluctuations in available resources (Mulkey et al. 1993); thus it fo llows that rates of photosynthesis and respiration are not the only factors determining a species successional status. Morphological variability emer ges when looking at specif ic leaf area (SLA), the ratio of leaf area to leaf ma ss, with light-demanding species displaying more variability in SLA than shade-tolerant species in altered lig ht environments (Walters and Reich 1999). Shade-tolerant species growing in understor y, low light conditions generally display a high SLA, a response providing greater surf ace area to increase in terception of light

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5 (Atwell et al. 1999; Henderson and Jose 2005) In contrast, light-demanding species growing in high light conditions generall y develop low SLA values, correlating to smaller, thicker leaves with greater palisad e tissue layers (Lambers et al. 1998). The reason for the variance in SLA is likely the resu lt of evolutionary features which lead to survivorship in shade. For shade-tolerant species, a low SLA is associated with long lived, tough, and herbivore resistant leaves, a ll factors conferring a competitive advantage to shade-tolerant species in low light (R eich et al. 1991; Kitajima 1994). Conversely, light-demanding species exhibit leaves with a short lifespan, limited resistance to pests or pathogens, and high turnover rates; all factor s proving advantageous in environments where resources are not limite d (Lambers et al. 1998). Whole Plant Level Acclimation to high light at the whole plan t level involves adjusting relative growth rate (RGR), biomass alloca tion, and altering canopy archit ecture and crown morphology. RGR, the rate of mass increase per unit mass pr esent, is generally much greater for lightdemanding than shade-tolerant species in hi gh resource environments while the variation between shade-tolerant and light-demanding species in low resource environments is generally minute (Lambers et al. 1998). In low resource (light) environments, shadetolerant species maintain si milar RGR to light-demanding sp ecies through variation in allocation and leaf morphology, a scenario whic h leads to maximizing the capture of the growth limiting resource of light (Lambers et al. 1998). Differences in biomass allocation to leaves, stems, and roots represent strategi es for energy capture, spatial exploration, and water and nutrient absorption (Grime1979; Tilman 1988). In low light or shaded environments, shoot growth takes priority, while in strong light the an tecedence is to root growth (Atwell et al. 1999). In response to shade, light-demanding species generally

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6 display an increase in stem el ongation (Lambers et al. 1998), while shade-tolerant species display much less plasticity, again likely as a result of evolutionary features selecting for defense over faster growth rates in low light (Kitajima 1994). In shaded environments, species generally distribute more biomass to leaves, creating a greater leaf area per unit plant mass (Popma and Bongers 1988; Osunkoya 1994). Species growing in high light, on the other hand, generally distribute a grea ter percentage of biomass to roots, compensating for higher transpiration loss occurri ng with increased radiation loads. Thus the response of plants to the environmen t is based on the search for components of growth, as plants responding to shade increas e biomass to leaves in order to access light and plants growing in high resource (lig ht) environments allocate relatively more biomass to roots in order to better capture th e limited resources of water and nutrients. Changes in canopy architecture represent th e search for limiting resources, with light-demanding species grown in low light a llocating more carbon to height growth and shade-tolerant species grown in low light distributing more resources to the growth of a few long branches (Zipperlen and Press 1996). Tree crown development of lightdemanding and shade-tolerant species follows two disparate paths based on preferred light environments. Light-demanding species growing in high light typically display deep, multilayered crown forms, with leaves scattered throughout the crown. Whereas, shade-tolerant specie s growing in low light typically contain shallow, mono-layered crowns, with a single layer of leaves at the periphery (Horn 1971; Poorter and Werger 1999). Successional Gradient Light in forests is very dynamic, often varying more dramatically than any other single plant resource (Chaz don et al. 1996), and species se parate themselves not only

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7 based upon their divergent light requirements but also upon their varied acclimation potentials (Valladares et al. 2002). From an ecophysiologica l viewpoint, species may be divided into two distinct groups of light-demanding and shade-tolerant (Swaine and Whitmore 1988). Light-demanding or gap re quiring species produce numerous small seeds, germinate in treefall light gaps, have high mortality rates, ar e shade intolerant and grow rapidly, while shade-tolerant species produce a small number of large seeds, germinate, develop, and display high survi vorship in deep shad e (Condit et al. 1995; Chazdon et al. 1996; Strauss-Debenedetti a nd Bazzaz 1996; Press et al. 1996; Whitmore 1996). The trend for capturing resources is widely divergent between light-demanding and shade-tolerant species. Light-demanding species exhi bit high potenti al rates of resource capture and growth, providing a built in mechanism for rapid growth and thus competitive advantage in high resource envi ronments. Conversely, shade-tolerant species display adaptations to low light environments with much lower potentials for resource capture, maintaining an advantag e through persistence and defense (Kitajima 1994). It has been suggested that species coexis t through partitioning of the light resource, optimizing performance based on specific light requirements (Denslow 1987). Partitioning of the light resour ce occurs in one of two ways. The first avenue emphasizes that species specialize to one end of the environmental gradient (light-demanding or shade-tolerant), while the second path represents an al teration of a particular species phenotype, or inherent range of change, to the light currently available at a particular site (Valladares 1999, 2000). Light-demanding and shad e-tolerant labels represent endpoints of a continuum of responses to light (Osunkoya 1994; Poorter 1999). As such, the

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8 phenotypic response to an alteration of the li ght environment may often provide greater insight towards a species successional standing, or assist in developing an understanding of tree species acclimation potential to changing light environments. The usefulness of simplifying into a light-d emanding/ shade-tolerant dichotomy is that characteristics a ssociated with each particular gr oup may be utilized to manage tree species as part of a resource management plan. The general pattern of forest development following logging operations depe nds upon the relative ab undance of tree species occupying the opposite ends of the pioneer-clim ax successional dichotomy (Swaine and Whitmore 1988). Pioneers depe nd upon open canopy conditions to facilitate germination of an abundant soil seed bank, while climax species operate through rapid growth of seedlings and saplings present at time of understory release created by large openings in the forest canopy (Dalling et al. 1998; Dekker and de Graaf 2003). In open conditions such as cleared forest land and land abandoned from agrarian uses, the situation becomes more complex, as the relative abundance of species of either successional stage is markedly reduced and often nonexistent. Adding to the complexity, for those involved in restoration, is the relatively miniscule information available concerning species regeneration dynamics and potential pathways of redevelopment. To mitigate complexity requires the deve lopment of information pertinent to rainforest restoration, such as determining spec ies tolerance to a range of light conditions. Measuring photosynthetic and morphol ogical responses can provide greater understanding of a species tole rance and growth to a range of light conditions and has been successfully used in forestry, agriculture, horticulture, and ecology (Boardman, 1977; Walters et al.1993; Walters and Reich 1996) Successful restoration of rainforest

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9 within Australia will depend upon a thorough unde rstanding of tree sp ecies response to limiting environmental variables such as wa ter, nutrients and light, along with the formulation of functional silvic ultural and regeneration strate gies to enable sustainable and long-term management of the rainforest re source. In this proj ect we will attempt to address the physiological and morphological res ponses of six subtropi cal rainforest trees to the light environment and elucidate the forest manageme nt opportunities where this information would be most beneficial. History of Australian Rainforest The total area of rainforest in Australia stands at approximately 2 million hectares (Webb and Tracey 1981). Two hundred years ago, the area containing rainforest may have been four times as large (Floyd 1990) The history of Australian rainforest landscape encompasses massive reduction in ra inforest, resulting from the development of an export market in Red Cedar, creation of an agrarian society, and resource extraction beyond sustainable levels. An initial and very important export product to the earliest European settlers was Toona australis -Red Cedar. Expansion in the search for Red Cedar directed early settlement patterns, beginning near Sydney and progressing northwards as supplies of timber dwindled (Adam 1992). Cedar-getting irrefutably resulted in significant reduction of rain forest stands; although the greater impact attributed to cedar-getting was identifica tion of rainforest stands which were consequently cleared to make way for agriculture and dairying (Adam 1992). Clearing of land for agrarian purposes led to profligate destruction of rainforest, leading to an almost 75% reduction of the orig inal rainforest existi ng prior to European settlement (Baur 1991). A major impetus for rainforest reduction was passage of the Land Settlement Act in 1860, which promoted settlement and an agricultural focus,

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10 leading to a bucolic relationship with th e land and moving settlement away from the nomadic lifestyle of the cedar-getters. Cl earing for agrarian purposes occurred in all rainforest areas along the east coast due to an inferred a ssociation of lush, verdant rainforest vegetation with high soil fertility a nd grand agricultural potential. Only rarely did this association hold as th e clearing process led to a subs tantial loss of nutrients and as a result limited productivity. Rainforest lands not cleared for agrarian purposes faced selective logging of commercially viable species, conversion to single species plantations, and conversion of low productivity rainforest to Eucalypt plantations (Adam 1992). History of Subtropical Rain forest in New South Wales The total area of rainforest within Ne w South Wales stands at approximately 200,000 hectares (Floyd 1990), an enormous reduc tion from an estimated pre-settlement value of 1,000,000 hectares (Baur 1991). In a region of New South Wales known as the Big Scrub, clearing for agriculture led to an even more prodigious reduction in rainforest, from 75,000 hectares pre-settlement to less than 300 hectares today (Floyd 1990). Activities which led to extensive reductio n of rainforest stands in New South Wales approximate those conducted across the re st of the Australian continent, with timber extraction and agrarian uses as th e guiding forces in resource use. The focus of forest management in Ne w South Wales today displays little resemblance to historical patterns focused on select species and the production of single species plantations. The current trends in rainforest management include creation of mixed species plantations, and enhanced re search into regenera tion requirements and silvicultural techniques for ma nagement of rainforest species A major catalyst for these newly emerging activities is an abundance of cleared and under utilized rainforest lands

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11 in various states of disrepair. Enormous potential exists to convert these areas back towards rainforest through restoration activities or in the development of mixed species plantations. Management options for rainforest species on public land within New South Wales excludes harvesting (Floyd 1990), resulting in an emphasis on preservation as national parks and World Natural Heritage Areas or towards rainforest restoration on public and private lands. Restoration activities are predicated on th e development and maintenance of self sustaining processes of forests towa rds a close approximati on of their original state. Restoration efforts generally seek rapid development of a canopy in order to facilitate the subsequent domi nation of a site by rainforest trees in the shortest time possible (Kooyman 1996). Thus a key considerati on to limit costs is an understanding of species regeneration strategies and general autecology in order to develop appropriate planting and silvicultural strategies. Mixed species plantations may serve as anot her viable alternativ e, especially when faced with restoration of large scale areas or when costs associated with restoration become excessive (Lamb 1998). Information pe rtinent to development of mixed species plantations include the value of timber species and potential growth rates of selected species (Glencross and Nichols, 2005). Efficient site utilizat ion is a guiding principle of mixed species plantations and can be achieved through appropriate spacing and understanding successional attributes of utilized species (Kee nan 1996). As with restoration, the best management strategy for utilizing rainforest species is maintaining, as a focal point, an understanding of the ecology of rainforest communities and their regenerative and successional processes.

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12 Rainforest Characteristics Rainforests consist of broken fragment s along the eastern coast of Australia, conceptualized as an archipelago amongst a sea of fire-prone eu calypt and ag ricultural lands (Bowman 2000). Once considered alien a nd invasive to the Australian flora, it is now understood that rainforest existed long before eucalyp t and other sclerophyllous vegetation (Webb and Tracey 1981). Distribu tion of rainforest lies over the entire latitudinal range of Australia, which includes climates from cool-temperate to tropical. These forests form a discontinuous distribut ion along the eastern fr inge of Australia, being restricted to areas ch aracterized by an average annua l rainfall greater than 1,300 mm and areas with low fire frequency (Sp echt and Specht 1999; Webb and Tracey 1994). There are four sub-formations of rain forest within New South Wales (cool temperate, warm temperate, subtropical, and dr y), with distribution of each sub-formation dependent upon six major factors (climate topography, microclimate, soil, fire, and competition) (Floyd 1989). Sub-tropical rainfo rest is the most well developed formation with distinguishing features that include o ccupation of sites with richer volcanic and alluvial soils (generally kraznosem soil (I sbell 1998)), rainfall in excess of 1300 mm annually, and sheltered situa tions generally below 900 m in altitude (Floyd 1989). Subtropical rainforest occurs in patches al ong the eastern coast from New South Wales to the uplands of far north Queensland (Lat 36 S to Lat 17 ) (Floyd, 1989). Tree species of this formation are conspicuously lofty, at 30-45 m height, typically with two to three levels arranged in a staggered rather than an even canopy (Floyd 1990). Tree composition of subtropical rainforest range s from 10 to 60 species and rarely does a single species dominate (Floyd 1989 ). Distinctiveness of this rainforest type arises through plank buttressing of many tree species and resplend ent, impenetrable canopies

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13 covered with epiphytes and thick woody vine s. Most species e xhibit large compound leaves, with entire leav es or leaflets more th an 7.5 cm long (Floyd 1990). Study Species Five tree species native to New South Wale s were selected for the study. A single species native to Queensland was included due to its utilization in restoration work throughout NSW. Species selection was based on presumed shade tolerance covering a broad successional gradient from early sec ondary (light-demanding) to later secondary and mature (shade-tolerant). The six species selected for the study included: Cryptocarya erythroxylon Pigeonberry Ash, a mature stage species generally relegated to the second story in canopy development and occasionally appearing in the first story, rarely developing as an emergent species (Floyd 1989); Elaeocarpus grandis Silver Quandong, an early secondary species occupying a wide range of sites and displaying a rapid growth habit (Floyd 1989); Flindersia brayleyana Queensland Maple, an early to late secondary species native to Queensland, which can tolerate a wide range of light conditions (Thompson et al. 1988); Flindersia schottiana Bumpy Ash, an early secondary species typically found in riverine and s ubtropical rainforest (Floyd 1989); Gmelina leichhardtii White Beech, a late secondary species which attains significant height dimensions and grows on a wide range of sites (Floyd 1989); Heritiera trifoliolatum White Booyong, a mature stage species which amasses large dimensions with prominent buttresses (Floyd 1989). All species are considered as particularly viable for restoration efforts and mixed species plantations (Kooyman 1996; Big Scrub Rainforest Landcare Group 1998). Few studies are available on the ecophys iological variability of subtropical rainforest species. Those developed have generally focused upon species native to

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14 Queensland, such as F. brayleyana (Thompson et al. 1988). An emphasis in this research project was placed upon subtropical rainfore st species native to northern New South Wales. The general format of previous st udies detailing growth (Thompson et al. 1988; Osunkoya et al. 1993) and photosynthetic performance of F. brayleyana (Thompson et al. 1988, 1992a, 1992 b; Swanborough et al. 1998) and H. trifoliolatum (Cunningham and Read 2002) under a range of light and temper ature conditions were closely approximated for all species included in th e current study. The background on F. brayleyana and H. trifoliolatum was elementary in nature while information on the remaining 4 species was decidedly less complete, with little k nown concerning growth and photosynthetic performance of C. erythroxylon, E. grandis, F. schottiana, and G. leichhardtii. Objectives and Hypotheses Successful establishment of these species in restoration projects and mixed species plantations requires detailed studies whic h evaluate their growth and physiological response to environmental variability. T hus, the broad objective of the study was to determine ecophysiological variability of the se lected subtropical rain forest tree species. A major focus of ecophysiologi cal variability pertains to changes in physiology and morphology of species to contrasting light environments. Thus, a thorough evaluation would identify within and between species vari ation to the light envi ronment in order to ascertain regeneration dynamics and successi onal aspects of subtropical rainforest species. In order to elaborate on species su ccessional characteristics, the current study evaluated rates of photosynthesi s and measurements of growth and biomass allocation of selected species under a range of light c onditions, with the following two specific objectives.

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15 Objective 1 The first objective focused on physiological vari ability within and be tween species, with a priority on the effect of light level on photosynthetic char acteristics of each species. The relevant hypotheses were: Hypothesis 1: Light-demanding (pioneer and early secondary) species will show higher rates of photosynthesis in high-light environments compared with the shadetolerant (late secondary and mature) species. Hypothesis 2: Shade-tolera nt (late secondary and matu re) species will display a narrower range of photosynthetic responses under three light environments than light-demanding (pioneer and early secondary) species. Objective 2 The second objective focused on morphological variability occurring within and between species. Variables evaluated incl uded growth and biomass allocation; focusing on relative growth rate (RGR), specific leaf area (SLA) and nutrient content of selected species. The relevant hypotheses were: Hypothesis 1: Light-demanding (pioneer a nd early secondary) species will achieve a higher RGR in the high light environment compared with the shade-tolerant (late secondary and mature) species. Hypothesis 2: Light-demanding species will achieve higher RGR in all light environments than will shade-tolerant species. Hypothesis 3: Light-demanding species wi ll display more variability in specific leaf area (SLA) under the three light treatments than shade-tolerant (later secondary and mature) species. The results of shadehouse and field-base d experiments conducted to test these hypotheses will be presented over two succeeding chapters. In Chapter 4, a summary of findings will be presented, followed by a disc ussion on the implications for management of subtropical rainforest species for re storation and mixed species plantations.

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16 CHAPTER 2 GROWTH AND PHOTOSYNTHETIC RESPONSES OF SIX AUSTRALIAN SUBTROPICAL RAINFOREST TREE SPE CIES TO A LIGHT GRADIENT Introduction Large areas of the worlds forests have been lost or degraded and landscapes everywhere are being simplified by current la nd-use practices (Lamb and Gilmour 2003). In many parts of the world this pattern of loss and destruction is just beginning, while elsewhere numerous countries are moving away from simplification of the landscape. Throughout the brief history of European imp act upon the Australian continent, sizable areas of rainforest have b een altered to satisfy resour ce needs. General patterns associated with colonization and subsequent resource extraction greatly influenced the loss and degradation of the Australian rainfo rest landscape. Today, land use practices are moving away from simplification of the land scape into the comple x and often uncharted territory of landscape re habilitation and rainfo rest restoration. Early land use patterns in Australia were geared towa rds progressive clearing of vast tracts of rainforest for agriculture, dairying, and timber (Adam 1992). An estimate on the extent of rainforest clearing sets a pre-settlement figure at 8 million hectares (Floyd 1990), while the area existing as rainfore st today is estimated at 2 million hectares (Webb and Tracey 1981). Abeyance of rain forest clearing, at least in state owned rainforest lands, coincided with placement of Australian rainforest on the World Heritage register (Erskine et al. 2005). The historical four fo ld reduction in areas consisting of rainforest (Floyd 1990) has left much of the Australian landscape bereft of a rainforest

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17 element. World Heritage listing assisted in conservation and pres ervation of existing rainforest, but a vast expanse of potential rain forest land within Australia sits unattended, either abandoned from agrarian uses or le ft degraded through exo tic species or weed invasion. Frequently, very larg e areas are in dire need of restoration and subsequent initiation of sustainable management for long-te rm benefits to the landscape (Smith et al. 2005). Restoration has been enacted in many regions of New South Wales since the late 1980s, mainly to restore small parcels of rainforest onto land controlled by the NSW National Parks and Wildlife Service. Howe ver, limited information concerning the ecology of rainforest species has often led to mixed results regarding these restoration efforts. Restoration attempts in Australia are often hampered by a paucity of ecophysiological data on rainforest species Relevant informa tion to ecophysiology centers on perturbations in the environment and the resulting vicissitude of plant species. Environmental perturbations, crea ting variation in the light environment, generally occur as disturbance events such as fire, cyclones, disease, and insect damage (Kimmins 1987); related vicissitude in plan t structure and function modul ate physiology and morphology of plant species (Atwell et al 1999). Restoration often faces a difficult task in perceiving or parlaying environmental vari ation without the bene fit of a baseline to compare with. Such is often the circumstan ce in restoration when little if any of the original environment exists. To mitigate the complex ity associated with restoring nonexistent or underrepresented ecosystems, current research seeks to determine baseline information of species response to environmental variation. Of general concern is plant species response to a range of light environments.

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18 Measuring photosynthetic and morphologi cal responses can provide a greater understanding of species tolerance to and gr owth under a range of light conditions and has been successfully used in forestry, ag riculture, horticulture, and ecology (Boardman 1977; Walters et al. 1993; Walters and Re ich 1996). Acquiring an understanding of species growth and physiological performance le ads to an enhanced opportunity to utilize rainforest species in resource management activities (Chazdon et al. 1996). In many silvicultural operations, an understanding of the ecophysiological and regeneration requirements of key species serves as a uni fying theme (Graaf 2000; Wadsworth 2001). Restoration objectives genera lly center upon initiating succ essional development where natural recovery is not underway and accel erating successional processes where it is (Lamb 1998). Thus any restoration effort mu st involve an understanding of successional processes and response of plant species to disturbance mechanisms. Disturbance is widely regarded as a primary mechanism for maintaining the diversity found in tropical and subtropical rainforest s (Connell 1970, 1978; Connell et al.1984). Disturbance regimes are also important in the evolution of tree species life history characteristics (Sheil and Van He ist 2000; Sheil and Burslem 2003). Environmental volatility arri ving from disturbance genera lly provides the impetus for facilitation or exclusion of tr ee species. One of the causal mechanisms of the discrepancy between rapid emergence and prolonged persis tence is species response to sun or shade conditions (Janzen and Vazquez-Yane s 1970; Hubbell 1979, 1998, 2001; Connell 1970, 1978; Connell et al. 1984). Rainforest species are typically depicted as belonging to one of two broad guild associations (Swaine and Whitmore 1988). Light-demanding or gap requiring species

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19 germinate in treefall light gaps have high mortality rates, ar e shade intolerant and grow rapidly, while shade-tolerant sp ecies germinate, grow, and have high survivorship in deep shade (Condit et al. 1995; Chazdon et al. 1996; Strauss-Debenedetti and Bazzaz 1996; Press et al. 1996; Whitmore 1996). Acclim ation of morphological and physiological traits of seedling leaves has been well doc umented for both early (light-demanding) and late (shade-tolerant) suc cessional species (Oberhauer and Strain 1984; Pearcy 1987; Strauss-Debendetti and Bazzaz 1991; Tur nbull et al. 1993; Kitajima 1994). Early successional (light-dem anding) species are found to be more plastic in their response to environmental change than la te successional (shade-tolerant) species (Strauss-Debendetti and Bazzaz 1991, 1996; Bazzaz 1996). For example, many comparative studies have shown that seed lings of light-demanding species maximize growth potential in low light by developing a high specific leaf ar ea (SLA) and high leaf area ratio (LAR) (Walters et al. 1993; Kitaji ma 1994). In addition they allocate more resources to new growth, with limited pr ovision to storage and defense (Augsburger 1984; Kobe 1997). Conversely, shade-tolerant species distribute very little to new growth and instead allocate towards traits associated with persistence (Walters and Reich 1999), such as the production of dense, dur able, well defended tissues (Augspurger 1984; Kitajima 1994). As witnessed in numerous st udies, the strategies of each guild are quite disparate and as such provide a window into pa tterns and processes of forested systems. The dynamics of regeneration are often infe rred after determin ing the sun versus shade characteristics of select species. Such a scenario serves as an elementary preview of the initial processes acc ounting for facilitation or excl usion of tree species and may provide a tool to predict fu ture stand composition and stru cture following disturbance.

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20 Disturbance events provide the appropriate e nvironment for a given species and lead to wide responses which govern tree diversity within the subtropical rainforest. An understanding of forest proce sses that maintain biodiversit y is crucial in conducting any management intervention and likely the most important is the intens ity and frequency of disturbance events. Conducting forest ma nagement based on perceived response to disturbance allows utilization of natural processes as the gu ide to appropriate resource management. Such a blueprint towards im itating the ecology of forests creates an allowance for using disturbance regimes as the primary tool for initiating and perpetuating forest structure and function (Baur, 1964; Whitmore 1990; Shiel and van Heist 2000). Therefore a key function of th e current research was to determine the response of species to alterations of the forest environment. The broad objective of the current st udy was to elucidate the ecophysiological response of six subtropical rainforest specie s to altered light environments. Such an objective was a response to the growing interest in rainfore st restoration and habitat rehabilitation efforts. In an effort to fac ilitate restoration efforts, the specific objective was to determine optimal light environments fo r growth of six subtr opical rainforest tree species, accomplished by comparing gr owth, morphological and photosynthetic responses of plants under natural and contro lled light environments. Two questions were asked during this study: (1) What photosynthetic adjustments do the six species make to different light environmen ts? (2) Do morphology, growth, and biomass differ for seedlings growing in varied light conditions?

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21 Methods Study Site The shadehouse study was conducted on the ca mpus of Southern Cross University, Lismore in northeast New South Wales, Au stralia (Long 153.27 East 28.81 South). The campus is situated in the subtropical rainfo rest region of NSW, at an altitude of 11 meters. Rainfall in Lismore averages ove r 1300 mm per year, monthly measurements during the study period were as follows: January (155.4 mm), February (183.6 mm), March (188.4 mm), and April (129.2 mm). The average temperature during the study period was (22.8C), with average temperatur es for each month as follows: January (24.4C), February (24C), March (22.7C), and April (20C). Study Species Six rainforest species were selected, ba sed upon the regeneration stages they are known to be associated with in a regenerating fo rest, including those th at form part of the mature forest (Floyd 1990; Kooyman 1996). Four main groups were recognized: pioneer, early secondary, late secondary, and mature phase species (Tab le 2-1). Pioneer and early secondary species are well suited to regenera te on disturbed and open sites, but are characterized by a short life-sp an (Whitmore 1983; Swaine et al. 1987). Conversely, late secondary and mature phase species are well suited to regenerate under shade, and may live considerably longer (Whitmore 1983; Sw aine et al. 1987). All species are considered particularly viable for restorati on and mixed species plan tation work within New South Wales (Kooyman 1996; Big Scr ub Rainforest Landcare Group 1998). Shadehouse Experiment The experiment was conducted in a random ized complete block design with three blocks (shadehouse). Seedlings were obtaine d from area nurseries, whereupon they were

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22 transferred from small planting containers and repotted in 1 gall on pots using a 70% standard potting mix (Yates General Purpose Potting Mix Australian Standard [Regular Grade]) to 30% gravel and sand combinati on. Each block (shadehouse) corresponded to one of three light treatments (60%, 30%, a nd 10% of full sunlight). The three light treatments (60%, 30%, and 10% full sunlight) were created using neutral density shade cloth. Seedlings were watered to maintain field ca pacity, and all seedlings were fertilized biweekly with Aquasol (Yates, Sydney, Australi a) Fast Acting Soluble Fertilizer with trace elements at a rate of 8 g to 5 L of water, applied to each seedling in 100 mL amounts. Photosynthetic Gas Exchange Light response curves were measured on a leaf area basis with a LICOR-6400 portable photosynthesis system (Li-Cor, Inc ., Lincoln, Nebraska USA) using the LIGHT CURVE automatic program with an artificial red/blue LED light source. Measurements were made at light levels of 2000, 1500, 1000, 500, 200, 100, 50, 20, and 0 mol m-2 s1. The leaf chamber environment was maintained at the following: CO2, 370 mol m-2 s-1, and temperature, 26 C. Photosynthetic measurements were made on 10 randomly selected seedlings of each species from each light treatment. Photosynthetic measurements were taken from 0700 to 1300 hours under clear to partly cloudy skies (Mar. 05 Apr. 05) on the most recent fully ex panded leaf. Prior to the start of each light response curve each selected leaf wa s placed in the leaf chamber at 1500 mol m-2 s-1 for 5 minutes. The order of treatments and s eedlings used were randomly selected each day.

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23 Growth Analysis Relative growth rate (RGR; biomass grow th per unit plant biomass, in mg g-1 day-1) was calculated according to Hunt (1978). The determination of RGR for each species required destructive sampling of three species from each treatment at the beginning (Jan. 05) and at the conclusion of the study (Apr. 05). Seedlings were separated into leaves, stems and roots, and dried at 70 C in a forced air oven for 48 h before quantifying dry mass. Roots were carefully washed prior to drying. The calculation of relative growth rates (RGR; Hunt 1982) were estimated as follows: RGR = ln(W2) ln(W1) t (days) ln(W2) = April 2005 dry mass ln(W1) = January 2005 dry mass t (days) = 1/11/2005 to 4/17/2005 = 96 days Leaf area was measured on a subset of leaves for each species in each light treatment using a LI-COR LI-3000 leaf area meter (Li-Cor Inc., Lincoln, NE USA). From the primary data, used to calculate RGR, the following variables were derived: specific leaf area (SLA; l eaf area/leaf mass, in cm2 g-1), leaf mass ratio (LMR; leaf mass/total plant mass, in g g-1), stem mass ratio (SMR; stem + petiole mass/total plant mass, in g g-1), and root mass ratio (RMR; root mass/total plant mass, in g g-1). These variables represent leaf display (SLA), a nd biomass allocation (LMR, SMR, RMR). Nutrient Content A representative sample of leaves was gath ered for all species in each treatment, and analyzed by the Environmental Analys is Laboratory located on the campus of Southern Cross University, Lismore, New South Wales, Australia. Samples were combusted at 550 C and digested with nitr ic acid to discern total nutrients. Concentration of nitrogen was determined using a LECO CNS2000 Analyzer. Nutrient

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24 analysis facilitated an evaluation of the relative proporti on of specific nutrients (nitrogen, phosphorous, potassium, and sulfur) of selected le aves from each treatment (Table A-1). Statistical Analysis Light curves were fitted by nonlinear regression using the Mitscherlich model equation (Sigma Plot 9.0, SSPS Inc., Chicago, Il linois USA) (Potvin et al. 1990; Peek et al. 2002; Aleric and Kirkman 2005): A = Amax [1 e-Aqe(PPF-LCP)] where Amax represents the asymptote of photosynthesis, Aqe corresponds to the initial slope of the curve, PPF represents the inci dent photosynthetic photon flux, LCP denotes the x intercept, where net photosynthesis is equal to 0, and A represents net photosynthesis. This model was used to identify the following parameters: Amax, the light saturated rate of photosynthesis, Aqe, the apparent quantum yield, and LCP, light compensation point. Morphological field data and photosynthetic plant responses were evaluated using a two-way ANOVA, with light treatment and sp ecies as independent variables (SAS 9.0, SAS Institute Inc., Cary, North Carolina USA). After ANOVA, differences among means were tested by Tukeys multiple comparison test. Mean values for root mass ratio (RMR), stem mass ratio (SMR), and leaf mass ratio (LMR) were calculated as the dry mass of root, stem, and leaves divided by the to tal dry mass, averaged for all seedlings in a treatment. Results Photosynthetic Response Light saturated rates of photosynthesis (Amax) increased for all species from 10% to 30% full sunlight, but decreased for most sp ecies moving from 30 to 60% full sunlight

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25 (F2,162=93.59, P < 0.0001)(Table 2-3, Figure 2-3 a nd 2-4). The two exceptions were Elaeocarpus grandis and Flindersia brayleyana both early secondary species, which achieved highest Amax in the 60% full sunlight treatmen t. The apparent quantum yield (Aqe) showed a significant difference within light treatment (F2,162=5.45, P < 0.05), with mean values for most species greatest in th e 60% full sunlight treatment and decreasing with decreasing light levels. The exception was for F. brayleyana which achieved peak Aqe in the 10% full sunlight treatment. Light compensation point (LCP) for species in the 60% full sunlight treatment was significantly greater (LCP) than species in the 30 and 10% full sunlight treatments (F2,162=105.3, P < 0.001). An exception occurred with Flindersia schottiana which achieved the greatest LCP in the 30% full sunlight treatment. Growth Patterns Stem diameter growth (Figure 2-2) for most species achieved a maximum in the 60% full sunlight treatment and decreased w ith decreasing light. The two exceptions were the two mature stage species ( Cryptocarya erythroxylon and Heritiera trifoliolatum ), which achieved peak stem diameter growth in the 30% full sunlight treatment. Stem height growth (Figure 2-2) displayed a similar patt ern with most species achieving maximum height growth in the 60% fu ll sunlight treatment, with the exception being F. brayleyana and Gmelina leichhardtii both of which displayed a peak in height growth in the 30% full sunlight treatment. Total plant dry biomass displayed a signi ficant difference among light treatments (F2,18=37.65, P < 0.0001), with most species displa ying a drop in total plant dry biomass when moving from 60% full sunlight to lower light levels. The only species displaying a

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26 different result was C. erythroxylon which displayed a peak in total plant dry biomass in the 30% full sunlight treatment. Relative growth rate differed between species (F5,18= 25.9, P < 0.0001) and light treatments (F5,18= 37.41, P < 0.0001). For most species RGR (Table 2-2, Figure 2-1) decreased when moving from 60% full sunl ight to lower light levels, with only C. erythroxylon a mature stage species showing a peak in RGR at 30% full sunlight. Early and late secondary species ( E. grandis F. brayleyana F. schottiana and G. leichhardtii ) displayed a significant di fference in specific leaf area (SLA) within species moving from high light to low light (F10,72 = 5.54, P < 0.0001). The two mature stage species ( C. erythroxylon and H. trifoliolatum ) did not differ in SLA in any of the light environments. Biomass allocation patterns displayed cont rasting results compared to common sun versus shade comparisons. Leaf mass rati o (LMR) displayed a si gnificant difference within light treatments (F2,18=7.53, P < 0.05), with most species allocating the greatest LMR in 60% full sunlight treatment and displaying a drop in the 30% and 10% full sunlight treatment. Root mass ratio (RMR ), showed a significant difference among light treatments (F2,18=5.0, P < 0.05), although it differed with LMR in that most species allocated a greater proportion to roots in the 10% full sunlight treatment as opposed to the 30% and 60% full sunlight treatments. Discussion Light is generally the most limiting resource to plant growth within rainforests (Yates et al. 1988). Therefore, the ability of plant species to acquire and utilize light is an important determinant of their comp etitive ability (Chazdon et al. 1996). Differences in responses to light availab ility involve correlative ecological and morphological

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27 characteristics of the studied species. A wide array of physiological responses was detected in the current study, corresponding to a light-demanding and shade-tolerant continuum (Osunkoya 1994). The physiological response observed fo r most species, to the three light environments, followed similar patterns to t hose reported for other sh ade-tolerant species (Oberbauer and Strain 1986; Tani et al. 2001; Al eric and Kirkman 2005). In general, these studies have reported a response pattern of increasing Amax with increasing light up to intermediate levels, followed by a decline in Amax at high light levels. Acclimation responses of shade-tolerant species do not generally involve in creasing photosynthetic capacity on a leaf dry mass basis (Sims a nd Pearcy 1991; Chazdon and Kaufmann 1993). In contrast, light-demanding species gene rally display a high capacity to modulate photosynthetic capacity in response to d ecreased light availa bility (Chazdon 1992; Turnbull et al. 1993). This wa s best exhibited in the cu rrent study by early secondary E. grandis which increased Amax from low to high light, achieving greatest Amax in the 60% treatment. Whereas, species displaying gr eater shade tolerance displayed much less physiological plasticity, w ith minute changes in Amax when moving from low to high light treatments. The ability, of a given sp ecies, to acclimate physiol ogically to altered light environments does not always provide a cl ear distinction between light-demanding and shade-tolerant species. Part of this may be explained by the fact that, except for true pioneer species; virtually all fo rest species must be able to tolerate low light conditions, at least during the earl y stages of their life history (C lark and Clark 1992). Therefore,

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28 determining shade tolerance may depend to a greater extent on the morphological and carbon allocation patterns of species growing under low light conditions (Kitajima 1994). Study seedlings displayed the typical s un-shade morphological responses reported in many other studies, with increased specific leaf area in low light, and enhanced relative growth rates in high resource environments (Walters et al. 1993; Beaudet and Messier 1998; Sack and Grubb 2002). SLA followed gene ral patterns for most species, with seedlings grown in low light displaying greater SLA than seedlings grown in heightened light environments. An exception to this pa ttern occurred with the two mature stage species ( C. erythroxylon and H. trifoliolatum ), which displayed limited variability in SLA under oscillating light conditions. This is co nsistent with a review by Walters and Reich (1999) in which shade-tolerant species were shown to be less variable in SLA when grown under contrasting light conditions. In contrast, th e early secondary and late secondary species ( E. grandis F. brayleyana, F. schottiana ., and G. leichhardtii ) displayed marked contrasts in SLA betw een low and high light treatments. RGR patterns, for most species, also displa yed a typical sun versus shade scenario, with high light grown plants exhibiting th e highest RGR and low light grown plants displaying the lowest RGR (Loach 1970). The reason for variation in RGR between light-demanding and shade-tolerant species may be accounted for by SLA, with species containing an inherent capacity for hi gh SLA generally displaying a greater RGR (Lambers and Poorter 1992; Reich et al. 1998). Seedlings within the current study closely approximated the association of SLA and RGR, with species achieving the highest RGR also displaying an increase in SLA under oscillating li ght conditions. In contrast, C. erythroxylon a mature stage species, displaye d a limited ability to alter SLA

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29 which corresponded to a reduction in RGR unde r variable light conditions. In many previous studies a relationship between RGR and mortality has been identified, with findings of a positive (Walters and Re ich 2000) and a negative (Kitajima 1994) relationship between survival in shade and RG R. In the current study, this pattern could not be deduced as mortality did not occur during the 96 days of the study, which may be related to the short le ngth of the experiment or light levels which were not sufficiently low enough to represent understory conditions (Sack and Grubb 2001). Biomass allocation patterns displayed little variability for half of the six species, based on light treatment. RMR vari ed in low light conditions for C. erythroxylon F. schottiana and G. leichhardtii with a peak for all species occurring in the 10% full sunlight treatment. This may account for the significant drop-off in RGR in low light for these species, as more resources were allocated to roots, a non limiti ng factor in low light situations, rather than provid ing greater allocation to leav es and thus providing greater potential for light capture (Popma and Bongers 1988; Osunkoya 1994). A similar pattern in LMR occurred for these species in the high light environment, w ith a peak occurring for all species in the 60% full sunlight treatment. An increase in LMR would likely correlate to a reduction in biomass allocated towards root mass, thus limiting the potential for greater water uptake under high radiation loads (Poorter 1999). An inherent difficulty occurs when attemp ting to extrapolate results gathered from controlled experiments to na tural conditions. Plants grown in shadehouses rarely experience the full complexity of the light environment within the forest, in respect to spectral quality and sunflecks (Ellswor th and Reich 1992; Wayne and Bazzaz 1993; Dalling et al. 1998; Bloor 2003). In addition, shadehouse conditions effectively exclude

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30 all causes of natural seedling mortality, such as herbivore damage or suboptimal growing seasons (Walters and Reich 2000). Nonetheless, shadehouse experiments have been shown to provide similar results as field studi es in terms of species rankings in growth parameters (Bloor 2003). Therefore, understa nding species response to sun versus shade conditions can assist toward development of guidelines concerning the amount of canopy cover necessary to create id eal growing conditions. For most species included in the study, ideal growing conditions fall within the range of 30 to 60% full sunlight. Thus initia l stand development for these species follows a range of amenable planting densities (tr ees/hectare), especially as a few species included in the current study continued to show significant growth in 10% full sunlight. For example, a successful planting scenar io may entail planting early secondary E. grandis and F. brayleyana in year one, followed by the introduction of early secondary F. schottiana and late secondary G. leichhardtti several years later. A diversifying mix of mature stage C. erythroxylon and H. trifoliolatum may follow at some much later date when the measured light environment in th e understory approximates 30% full sunlight or less. Similarly, silvicultural manipul ations of stand dens ity in basal area (m2/hectare) provide for a full range of options from ca nopy retention maintaining light conditions at 10% full sunlight and thereby assisting ma ture stage species or maintaining light conditions near 60% full sunlight and benefiting F. brayleyana and G. leichhardtii In the case of E. grandis little canopy retention may be neces sary as it appears to respond well to light conditions at or greater than 60% full sunlight. The general results of this study indicate promise for inclusion of study sp ecies in rainforest restoration activities and in the development of mixed species plantations. Ascertaining a complete

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31 understanding of species performance will requi re further research into characteristics leading to species growth performance and those characteristics which provide for maintenance, persistence, and storage (K itajima 1994; Kobe 1997). In light of this, further research should be conducted for subt ropical rainforest species under natural conditions to further elucidate the response of species to herbi vores, pathogens, and nutrient and water limitation. Table 2-1. Life history da ta for the study species. Species Symbol Max height (m) Max DBH (cm) Successional stage Cryptocarya erythroxylon Ce 35 125 Mature Elaeocarpus grandis Eg 35 200 Early secondary Flindersia brayleyana Fb 40 250 Late secondary Flindersia schottiana Fs 45 100 Early secondary Gmelina leichhardtii Gl 40 150 Late secondary Heritiera trifoliolatum Ht 45 200 Mature *Adapted from Floyd 1990 and Kooyman 1996.

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32 Table 2-2. Total dry biomass production (g), relative growth rate between 0 to 96 days (RGR, mg g-1 d-1), specific leaf area (SLA, cm2 g-1) leaf mass ratio (LMR), stem mass ratio (SMR), root mass ratio (RMR), total stem height (cm), and total stem diameter (mm) shown by the six species at 96 days of growth under high light (HL 60%), medium light (ML 30%), and low light (LL 10%). Species codes as given in Tabl e 2-1. Small letters show significant differences at P < 0.05 among treatment s for each species, after ANOVA and Tukey's multiple comparison test. Speci es arrangement is in increasing order of RGR. Species Gl Eg Fb Ht Fs Ce Total Biomass HL 36.02a 13.49a 5.10a 22.04a 16.29a 32.85b ML 33.38a 9.49a 5.03a 19.43ab 14.42ab 41.24a LL 16.61b 8.80a 3.05a 13.56b 8.56b 27.45b RGR HL 11.37ab 10.12a 7.17ab 6.04a 4.80ab (-)0.83a ML 10.56a 6.66ab 5.29a 4.73ab 3.66a 1.54a LL 3.29b 5.82b 0.79b 0.99b (-)1.83b (-)2.71b SLA HL 84.6c 133.6c 117.8b 100.5a 115.3c 110.7a ML 124.2b 192.7b 127.7b 122a 150.7b 111.8a LL 185.5a 242a 176.7a 117.8a 184.3a 118.2a LMR HL 0.31a 0.37a 0.27a 0.21a 0.42a 0.35a ML 0.24a 0.32a 0.31a 0.23a 0.35a 0.27a LL 0.16ab 0.37a 0.29a 0.23a 0.28ab 0.24ab SMR HL 0.37a 0.27a 0.32a 0.37a 0.32a 0.38a ML 0.41a 0.30a 0.32a 0.34a 0.33a 0.36a LL 0.37a 0.27a 0.36a 0.34a 0.35a 0.40a RMR HL 0.33ab 0.37a 0.42a 0.42a 0.26b 0.28b ML 0.36b 0.39a 0.38a 0.43a 0.33ab 0.39ab LL 0.47a 0.37a 0.35a 0.43a 0.38a 0.37a Diameter Growth HL 2.64a 2.47a 1.55a 2.21b 2.11a 2.10a ML 2.29a 2.46a 1.47a 2.48a 1.88a 2.29a LL 1.12b 2.12a 0.90a 0.97b 1.47a 1.59a Height Growth HL 10.72b 23.56a 4.73a 21.41a 7.54a 5.69a ML 19.21a 14.81b 4.83a 16.37a 5.01a 5.21a LL 12.26b 17.18b 4.06a 9.21b 5.43a 5.55a

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33 Table 2-3. Leaf-level photos ynthetic parameters. Light sa turated rate of photosynthesis (Amax, mol CO2 m-2 s-1), apparent quantum yield (Aqe, (mol CO2 m-2 s1)/(mol m-2 s-1)), and light compensa tion point (LCP, mol m-2 s-1) shown by the six species grown under high light (HL 60% full sunlight), medium light (ML 30% full sunlight), and lo w light (LL 10% full sunlight). Species codes as given in Table 21. Small letters show significant differences at P < 0.05 among treatment s for each species, after ANOVA and Tukeys multiple comparison test. Species Gl Eg Fb Ht Fs Ce Amax HL 8.44b 9.36a 3.76a 6.45ab 6.10b 4.79b ML 9.36a 5.42b 2.76b 6.57a 7.66a 5.72a LL 8.96ab 4.98b 2.08c 3.34b 6.42b 4.34b Aqe HL 0.0056a 0.0053a 0.0109a 0.0049a 0.0080a 0.0082a ML 0.0047a 0.0110a 0.0092ab0.0071a 0.0046a 0.0070a LL 0.0058a 0.0128a 0.0444b 0.0123a 0.0072a 0.0060a LCP HL 17.80a 16.42a 18.42a 23.60a 9.96ab 15.27a ML 9.60b 8.30b 8.75b 12.30b 10.05a 9.50b LL 5.15b 3.95b 5.15b 8.70b 4.80b 7.10b

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34 -6 -4 -2 0 2 4 6 8 10 12 14Relative Growth Rate (mg g-1 day-1) GlEgFbHt FsCe 60 % 30 % 10 % Figure 2-1. Relative growth rate (mean (SE)) of seedlings of six Australian subtropical rainforest trees, grown at 60%, 30%, and 10% of full sunlight. Species codes as given in Table 2-1.

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35 0 1 2 3 4Diameter Growth (mm) Gl Eg FbHt Fs Ce 60 % 30 % 10 % 0 5 10 15 20 25 30Height Growth (cm) GlEgFbHtFs Ce 60 % 30 % 10 % Figure 2-2. A) Diameter grow th in (mm). B) Height gr owth in (cm) (mean (SE)) of seedlings of six Australian subtropica l rainforest trees grown at 60%, 30%, and 10% full sunlight. Species codes as given in Table 2-1. A B

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36 Figure 2-3. Light response curve of photosynthesis as a function of PPFD for A) Elaeocarpus grandis B) Flindersia schottiana and C) Gmelina leichhardtii grown under three light treatments. Data points represent m eans +/standard errors (N=10). Light curves were f itted by non-linear regression using the Mitscherlich equation. A B C

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37 Figure 2-4. Light response curve of photosynthesis as a function of PPFD for A) Flindersia brayleyana B) Heritiera trifoliolatum and C) Cryptocarya erythroxylon grown under three light treatments Data points represent means +/standard errors (N=10) Light curves were fitted by non-linear regression using the Mitscherlich equation. A B C

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38 CHAPTER 3 POTENTIAL FOR SUBTROPICAL RAINFOREST RESTORATION ON ABANDONED AGRICULTURAL LANDS IN NEW SOUTH WALES, AUSTRALIA Introduction Development of restoration focused activ ities is the antith etical response to progressive degradation and lo ss of forested areas within New South Wales. During the short duration of European se ttlement, rainforest lands w ithin NSW decreased by more than 750,000 ha (Baur 1991). In an area of New South Wales known as the Big Scrub, rainforests diminished from a pre-settlement figure of 75,000 ha to less than 300 ha today (Floyd 1990). The prospects for conservation beyond remnan t rainforest relics remained uncertain until the late 1970s and early 1980s, whereupon a vocal majority began to question traditional forestry operations (Adam 1992) Following fervent public opposition over rainforest logging, the New South Wales governme nt enacted legislation in the late 1980s placing state-owned subtropical rainforest s on the World Herita ge register, and subsequently halting timber extraction on st ate-owned subtropical rainforests (Adam 1992; Erskine et al. 2005). The loss of a tim ber resource on state-owned lands created a novel opportunity for growing rainforest trees in plantations to suppl y high-value cabinet timbers, along with the chan ce to restore some diversity to abandoned and degraded agricultural lands (Glenc ross and Nichols 2005; Erskine et al. 2005). The biggest challenge facing rainforest re storation today is limited information on growth and performance of rainforest spec ies. A flourishing opportunity exists, for

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39 restoration and rehabilitation of degraded rainforest lands, contingent upon an understanding of the ecology of rainforest sp ecies and an elucidation of silvicultural requirements for long-term maintenance and sust ainability of subtropical rainforest. The burgeoning potential results from a proliferation of formerly forested areas which were once used for agriculture and dairying, and are now abandoned and exist bereft of any rainforest element (Kooyman 1996; Erskine et al. 2005). Rainforest restoration becomes an option when degraded and damaged forest landscapes display reduced productivity, biodiversity, and limited return of goods and services (L amb and Gilmour 2003). Much of the formerly forested land within New South Wales embodies a landscape of limited productivity and major reduction in biodiversity. These site s present an opportunity to implement restoration activities aimed at reme diation and rehabilita tion of the degraded and damaged condition under which they now exist (Kooyman 1996; Big Scrub Rainforest Landcare Group 1998). To moderate complexity associated with restoration activities, numerous studies have detailed photosynthetic and growth responses to light e nvironments (Walters et al. 1993; Walters and Reich 1996; Valladares et al. 2002). Measuring photosynthetic and growth responses can reveal valuable inform ation concerning tolerance and growth of species to a range of habita t conditions (Aleric and Kirkma n 2005). Rainforest trees are generally classified into two functiona l groups, based on their germination and establishment requirements (Swaine and Whitmore 1988). Shad-tolerant species can grow, germinate, and survive in a low li ght environment, whereas light-demanding species require a high light environment to establish (Poorter 1999). Discerning between the two functional groups allows an interpreta tion of appropriate silvicultural regimes for

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40 growth and performance of rainforest trees, thus enhancing the poten tial utilization of subtropical rainforest tree speci es in forest management or ra inforest restoration projects (Chazdon et al. 1996). To aid the development of suitable silvicu ltural regimes and rainforest restoration projects within New South Wales, the st udy assessed the photosynt hetic response of 7 subtropical rainforest tree species growing in an under-uti lized agricultural field in northern New South Wales, Australia. Materials and Methods Study Site The field study was conducted between March 2005 and April 2005 at an underutilized agricultural field, which begi nning in May 2002 was converted towards a subtropical rainforest restora tion site. The field site is located approximately 9 km southwest of Mullumbimby, NSW and approximately 12 km northeast of Byron Bay, NSW. The field site is situated in the subt ropical rainforest region of northeastern NSW, at an altitude of 35 meters. Rainfall in th e study region averages over 1700 mm per year. The average annual temperature in the st udy region is (23.7C) with average annual temperature in March of (26.5C) and av erage in April of (24.5C) (Bureau of Meteorology, Australia). Soils of the regi on consist of deep, well-drained krasnozems (FAO classification-(Luvisols), USDA classi fication-(Rhodoxeralfs) derived mainly from tertiary basalt flows (Isbell 1998). Species Seven rainforest species we re selected, based on the re generation stages they are known to be associated with in a regenerating fo rest, including those th at form part of the mature forest (Floyd 1990; Kooyman 1996). Four main groups were recognized: pioneer,

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41 early secondary, late secondary and mature phase species (Table 3-1). Pioneer and early secondary species are well suited to regenera te on disturbed and open sites, but are characterized by a short life-sp an (Whitmore 1983; Swaine et al. 1987). Conversely, late secondary and mature phase species are well suited to regenerate under shade, and may live considerably longer (Whitmore 1983; Sw aine et al. 1987). All species are considered particularly viable for restorati on and mixed species plan tation work within New South Wales (Kooyman, 1996; Big Sc rub Rainforest Landcare Group 1998). Photosynthetic Gas Exchange Light response curves were measured on a leaf area basis with a LICOR-6400 portable photosynthesis system (Li-Cor, Inc ., Lincoln, Nebraska USA) using the LIGHT CURVE automatic program with an artificial red/blue LED light source. Measurements were made at light levels of 2000, 1500, 1000, 500, 200, 100, 50, 20, and 0 mol m-2 s1. The leaf chamber environment was maintained at the following: CO2, 370 mol m-2 s-1, and temperature, 26 C. Photosynthetic measurements were made on 5 randomly selected 3-year old saplings of each species Photosynthetic measurements were taken from 0700 to 1300 hours under clear to partly cloudy skies (March 2005 to April 2005) on the most recent fully expanded leaf. Prior to the start of each light response curve each selected leaf was placed in the leaf chamber at 1500 mol m-2 s-1 for 5 minutes. The order of treatments and the replicates of 3-year-old saplings used were randomly selected each day. Nutrient Content A representative sample of leaves was gath ered for all seven species, and analyzed by the Environmental Analysis Laboratory located on the campus of Southern Cross

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42 University, Lismore, New South Wales, Aust ralia. Samples were combusted at 550C and digested with nitric acid to discern total nutrients. Concentrat ion of nitrogen was determined using a LECO CNS2000 Analyzer. Nu trient analysis facilitated an evaluation of the relative proportion of specific nutrients (nitr ogen, phosphorous, potassium, and sulphur) of selected leaves from the 75% full sunlight treatment (Table A-2). Statistical Analysis Light curves were fitted by nonlinear regression using the Mitscherlich model equation (Sigma Plot 9.0, SSPS Inc., Chicago, Il linois USA) (Potvin et al. 1990; Peek et al. 2002; Aleric and Kirkman 2005): A = Amax [1 e-Aqe(PPF-LCP)] where Amax represents the asymptote of photosynthesis, Aqe corresponds to the initial slope of the curve, PPF represents the inci dent photosynthetic photon flux, LCP denotes the x intercept, where net photosynthesis is equal to 0, and A represents net photosynthesis. This model was used to identify the following parameters: Amax, the light saturated rate of photosynthesis, Aqe, the apparent quantum yield, and LCP, light compensation point. Analysis of variance (ANOVA) was used to compare the effect of light environment on photosynthetic characteristic s and growth parameters (SAS 9.0, SAS Institute Inc., Cary, North Carolina USA). Results An analysis of species height at three y ears showed a significant difference between species (F6,105=28.21, P<0.0001) with a ra nge (Figure 3-1) fr om 2.73 m to 5.26 m. Diameter after 3 years also displayed a significant difference between species (F6,105=32.15, P<0.0001) with a range (Figure 31) from 0.0024 m to 0.0070 m. Stem

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43 volume index (SVI) (Figure 3-2) at three years displayed wide variability between species (F6,105=24.67, P<0.0001) with Lophostemom. confertus providing peak SVI, followed by Elaeocarpus grandis Flindersia brayleyana and Gmelina leichhardtii Species displaying reduced SVI values included Flindersia schottiana Heritiera trifoliolatum and Castanospermum australe Light saturated rates of photosynthesis (Amax) displayed a significant difference between species (F6,28=62.21, P<0.0001), with a range from 5.68 to 17.16 mol CO2 m-2 s-1 (Table 3-2)(Figures 3-3, 3-4 and 3-5). Patterns of photosynthetic response closely approximated results gathered from a shad ehouse experiment where a subset of the sample species were studied (Kelly et al. 2006), with early seconda ry species displaying greater light saturated rates of photosynthesis (Amax) than late secondary and mature stage species. L. confertus provided an exception to this pattern, exhibiting a higher Amax than all study species besides E. grandis an early secondary species. In addition to between species variability in light sa turated rates of photosynthesis, the apparent quantum yield (Aqe) displayed a significant difference between species (F6,28=27.52, P < 0.0001), along with the witnessing of a significant differe nce between species in light compensation point (LCP) (F6,28=7.59, P < 0.0001). Discussion Rainforest species experience dramatic va riability throughout thei r lifetimes, from daily changes in sunfleck occurrence to mo re drastic changes in light availability resulting from large-scale canopy disturbance (Chazdon et al. 1996). Rainforest species respond to these environmental perturbati ons through acclimation, which provides for environmentally-induced changes in photosynt hetic utilization of light, based upon the light environment under which leaves deve lop (Chazdon et al. 1996). Species which

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44 have developed under high light generally have higher light saturated rates of photosynthesis (Amax) and higher light compensation points (LCP) (Lambers et al. 1998). This pattern remained consistent in th e field study, with species common to the shadehouse and field study displaying higher light saturated rates of photosynthesis and higher light compensation points under ope n grown conditions. Maximum rates of photosynthesis for species in the field study ranged from 5.68 to 17.16 mol CO2 m-2 s-1; closely approximating the 10-15 mol CO2 m-2 s-1 reported for sun leaves (Loach 1967; Larcher 1995). Many previous studies have dictated enhanced performance of sun grown individuals, although a demarca tion exists between early an d late successional species (Strauss-Debendetti and Bazzaz 1991; Poorte r and Oberbauer 1993). Early successional species generally exhibit greater plasticity in photosynthetic capacity compared to later succesional species (Chazdon et al. 1996). Predictable patterns followed throughout the field study, with early successional species displaying greater Amax compared with late successional and mature stage species. An exception occurred with L. confertus a mature stage species, which displayed comparable Amax to early and late successional species. Similar findings occurred with the late successiona l Australian species Acmena ingens (Turnbull 1991), suggesting that the extent of photosynthetic plasticity exhibited by a species is not always a good predictor of its acclimation potential (Chazdon et al. 1996). Species grown in field conditions experi ence greater environmental perturbation, through decreased soil moisture, increased herbivore damage, and increased competition for water and nutrients from surrounding vegeta tion. In addition, they experience greater

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45 complexity in the light environment, in term s of spectral quality a nd sunflecks (Dalling et al. 1999; Bloor 2003). Thus, identifying sp ecies response to natural environmental perturbation can provide further eviden ce towards determining the potential of subtropical rainforest species in rainfore st restoration and mixed species plantation efforts. Based on the results of the field study, mo st species segregate into two distinct groups of light-demanding and shade-tole rant. Light-demanding species include E. grandis F. schottiana and include the interlopers: L. confertus a mature stage species, and G. leichhardtii a late successional species. The shade-tolerant group includes C. australe F. brayleyana and H. trifoliolatum Most species represent a continuum of responses to light, thus sugge sting a cataloguing as generalist s rather than specialists (Osunkoya et al. 1994). In the tr opical rainforest it has been s uggested that most if not all species may be catalogued as generalists rath er than specialists (Chazdon et al. 1996). Many species exhibit ample plasticity when responding to light availability at a given site, thus, allowing greater expl oitation of more vari able environments than species with narrower acclimation responses (Atwell et al. 1999). The species in the field study displayed gr eat potential for acclim ation to high light environments, thus indicating that a wide ra nge of planting and silv icultural mechanisms might be effective in managing these species. For example, the potential of these species under close to full sunlight conditions (75% fu ll sunlight) allows fo r planting in cleared or under utilized agricultural fi elds, in large gaps of remnant rainforest, and near edges of existing rainforest remnants. Photosynthetic and growth potential of study species under close to full sunlight conditions provides for use in rainforest restoration across numerous

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46 sites devoid of rainforest ve getation. The responses of E. grandis G. leichhardtii and L. confertus under close to full sunlight conditions (75% full sunlight ) provides strong support on their potential for rapid growth a nd related rapid canopy closure, whereas the remaining species appear better suited fo r plantings under an intact canopy or in situations where the light environment remains at levels less than 75% full sunlight. To understand more fully the potential of these se ven rainforest species under close to full sunlight conditions, further research should be conducted evaluating influencing factors to photosynthetic performance such as cons traints by ontogeny (Ri ce et al. 1993; Gedroc et al. 1996), by resource av ailability (Bloom et al. 1985), and by loss to pests and pathogens. Determining the impact of thes e factors will greatly facilitate a deeper understanding of species ecology, natural history, distribution, and growth and performance potential.

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47 Table 3-1. Life history data for the study species. Species Symbol Max height (m) Max DBH (cm) Successional stage Castanospermum australe Ca 35 100 Mature Elaeocarpus grandis Eg 35 200 Early secondary Flindersia brayleyana Fb 40 250 Late secondary Flindersia schottiana Fs 45 100 Early secondary Gmelina leichhardtii Gl 40 150 Late secondary Heritiera trifoliolatum Ht 45 200 Mature Lophostemom confertus Lc 40 200 Mature *Adapted from Floyd 1990 and Kooyman 1996. Table 3-2. Leaf-level photos ynthetic parameters: Light satu rated rate of photosynthesis (Amax, mol CO2 m-2 s-1), apparent quantum yield (Aqe, (mol CO2 m-2 s1)/(mol m-2 s-1)), and light compensation point (LCP, mol m-2 s-1) shown by the seven species grown under 75% full s unlight. Species codes as given in Table 3-1. Species Ca Eg Fb Fs Gl Ht Lc Amax 9.85 17.16 8.50 13.41 12.77 5.68 16.91 Aqe 0.0025 0.0025 0.0029 0.0033 0.0025 0.0056 0.0024 LCP 25.90 20.50 19.16 20.50 18.70 28.50 29.80

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48 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.081Diameter (m)LcFbEgGlFsHtCa 0.00 1.00 2.00 3.00 4.00 5.00 6.00 1Height (m)LcFb Eg G l FsHt Ca Figure 3-1. A) Diameter growth (m) and B) height growth (m) (mean (+/SE)) of seedlings of seven Australian subtropical rainforest trees at 3 years, grown under 75% full sunlight. Species codes as given in Table 3-1. A B

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49 0.0000 0.0050 0.0100 0.0150 0.0200 0.0250 0.0300 0.03501Stem Volume Index LcFbEgGlFsHtCa Figure 3-2. Stem Volume Index (SVI) (m3) (mean (+/SE)) of seedlings of seven Australian subtropical rainforest tr ees at 3 years, grown under 75% full sunlight. Species codes as given in Table 3-1.

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50 Figure 3-3. Light response curve of photosynthesis as a function of PPFD for A) Elaeocarpus grandis B) Flindersia schottiana and C) Gmelina leichhardtii grown under 75% full sunlight. Data points represent means +/standard errors (N=5). Light curves were fi tted by non-linear regression using the Mitscherlich equation. A B C

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51 Figure 3-4. Light response curve of photosynthesis as a function of PPFD for A) Flindersia brayleyana and B) Lophostemom confertus grown under 75% full sunlight. Data points represent means +/standard errors (N=5). Light curves were fitted by non-linear regression using the Mitscherlich equation. B A

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52 Figure 3-5. Light response curve of photosynthesis as a function of PPFD for A) Castanospermum australe and B) Heritiera trifoliolatum grown under 75% full sunlight. Data points represent mean s +/standard errors (N=5). Light curves were fitted by non-linear regression using the Mitscherlich equation. B A

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53 CHAPTER 4 SUMMARY AND CONCLUSIONS Shadehouse and field studies were co nducted, to elucidate ecophysiological variability of subtropical rainforest trees to altering light environments, in order to augment current knowledge of sp ecies potential for rainforest restoration projects and mixed species plantations. Presumed respons es of rainforest species to sun or shade followed those developed by Swaine and Whitm ore (1988), in which species are divided into a light-demanding and shade-tolerant di chotomy. The current study also included an additional caveat, that species response to sun or shade depends upon acclimation potential, which is equall y affected by constraint s during ontogeny, by resource availability, and by loss to herbivores (Bloor and Grubb 2004). To evaluate and ascertain acclimation potential, experiments were conducted under controlled conditions in a shadehouse and under natural cond itions at a field site. Many past studies have utilized informa tion on growth and photosynthetic potential to ascribe ideal growing and silvicultural situ ations in which to enhance performance of species (Boardman 1977; Walters et al. 1993; Walters and Reich 1996). Rainforest species are typically depicted as belonging to one of two broad guild associations (Swaine and Whitmore 1988). Light-demanding or gap requiring species germinate in treefall light gaps, have high mortality rates, are light-demanding and grow rapidly, while shade-tolerant species germinat e, grow, and have high survivorship in deep shade (Condit et al. 1995; Chazdon et al. 1996; Strauss-Debe nedetti and Bazzaz 1996; Press et al. 1996; Whitmore 1996). Two questions were asked during the study to fu rther elaborate on

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54 species successional status a nd acclimation potential: 1) What photosynthetic adjustments are made by study species in response to vari ation in the light environment? 2) Do morphology, growth, and biomass differ for seedlings growing in different light environments? In this study, hypotheses to aforemen tioned questions focused upon successional attributes and acclimation potential of st udy species. In general, these hypotheses predicted enhanced photosynthetic rates of early successional species in high light and greater potential for physiological acclimation of early succes sional species across a light gradient. Hypotheses on growth parameters, predicted heightened relative growth rates for early successional species across a lig ht gradient, with ample potential for morphological plasticity across a light gr adient. Conversely, hypotheses for shadetolerant species depicted re duced photosynthetic rates in high light and limited potential for physiological acclimation across a light grad ient. In addition, shade-tolerant species were predicted to display limited variation in growth parameters and limited ability for morphological plasticity acr oss a light gradient. Based on results acquired from the shad ehouse study, physiological responses fall between an opaque demarcation of ea rly and late successional species. Elaeocarpus grandis provided a clear representation of an early successional species, with marked increase in Amax in high light and an ability to do wn regulate photosynthetic machinery in low light conditions. The remaining species ( Flindersia brayleyana, Flindersia schottiana, Gmelina leichhardtii and Heritiera trifoliolatum ) were better represented as falling along a shade-tolerant continuum, with limited ability to adjust physiologically to an increase or decrease in light, maintaining similar Amax across all light environments.

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55 Morphological change across a light grad ient, in the shadehouse experiment, provided greater discernment of common successi onal patterns. In high light, all species displayed a peak in RGR, except for th e facultative shade-tolerant species Cryptocarya erythroxylon which displayed a peak in 30% full sunlight. Early and late secondary species displayed heightened RGR compared to mature stage species, which may be accounted for by the inherent capacity fo r high SLA in early successional species (Lambers and Poorter 1992; Reich et al. 1998). Patterns in SLA closely approximated the perceived early and late successional di chotomy. In the shadehouse study, early and late secondary species ( E. grandis, F. brayleyana, F. schottiana and G. leichhardtii ) displayed an ability to modulate SLA when moving from high to low light, whereas mature stage species ( C. erythroxylon and H. trifoliolatum ) displayed limited potential to modulate SLA in response to variable light. Results from the field study closely corr oborated observations from the shadehouse study. Species in the shadehouse which displayed maximum Amax in the 60% full sunlight treatment ( E. grandis and F. brayleyana ) continued to display heightened Amax in the 75% full sunlight field study. Remain ing species occurring in both studies ( F. schottiana, G. leichhardtti and H. trifoliolatum ) displayed enhanced Amax under high light conditions present in the field study; in contrast to a peak in Amax under moderate light (30% full sunlight) in the shadehouse study. This c ondition strongly suggests the influence of ontogeny on acclimation potential of study species (Rice et al. 1993; Gedroc et al. 1996), as species developing under high light conditions genera lly display increased light saturated rates of photosynthesis (Amax) and light compensation points (LCP) (Lambers et al. 1998). Species eval uated solely in the field study ( Castanospermum

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56 australe and Lophostemom confertus ) also displayed heightened Amax, closely approximating the typical range for sun leaves of 10-15 mol CO2 m-2 s-1 (Loach 1967; Larcher 1995). This study provides important insight into po tential of subtropical rainforest species to a range of light environm ents. Results show that most species belong to a shadetolerant constituency, with an ability to grow and persist across a wide range of light environments. Growth and photosynthetic performance of most species reached a maximum in 30% to 60% full sunlight found in shadehouse conditions. Species under natural conditions displayed an ability to acclimate to heightened light conditions, reaching their highest Amax in 75% full sunlight, and thus providing credence to the influence of ontogeny on species performance. In conclusion, study species offer a wide range of potential planting scenarios and silvicultural options, with am ple potential to achieve rapid canopy closure and restoration goals. This study indicates prom ise for inclusion of study species in rainforest restoration activities and in the development of mixed species plantations. Ascertaining a complete understanding of species performance will requi re further research into characteristics leading to species growth performance and those characteristics which provide for maintenance, persistence, and storage (K itajima 1994; Kobe 1997). In light of this, further research should be conducted for subtr opical rainforest species to elucidate the response of species to pests, pat hogens, and resour ce availability.

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57 APPENDIX NUTRIENT CONCENTRATION Table A-1. Total nutrient concen tration in leaves of six s ubtropical rainfo rest species grown under HL (60%), ML (30%) a nd LL (10%) full sunlight. Species codes as given in Table 2-1. Species Units Gl Eg Fb Ht Fs Ce Nitrogen % HL 1.24 1.12 0.87 2.23 1.43 1.43 ML 1.58 1.25 1.04 2.44 1.62 1.61 LL 2.00 1.84 0.87 2.07 1.71 1.83 Phosphorus % HL 0.05 0.09 0.05 0.11 0.19 0.09 ML 0.07 0.10 0.06 0.10 0.16 0.12 LL 0.08 0.10 0.06 0.08 0.16 0.11 Potassium % HL 0.44 0.60 0.25 0.92 0.68 1.03 ML 0.82 1.04 0.30 0.98 0.54 1.20 LL 0.89 0.99 0.31 0.89 0.46 1.51 Sulphur % HL 0.10 0.13 0.08 0.15 0.11 0.12 ML 0.10 0.13 0.12 0.17 0.14 0.16 LL 0.13 0.17 0.12 0.15 0.15 0.14

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58 Table A-2. Total nutrient concen tration in leaves of seven s ubtropical rainforest species grown under 75% full sunlight. Specie s codes as given in Table 3-1. Species Nutrient Units Ca Eg Fb Fs Gl Ht Lc Nitrogen % 2.32 1.98 2.17 2.31 1.47 1.63 1.45 Phosphorus % 0.14 0.16 0.11 0.15 0.10 0.10 0.11 Potassium % 0.57 0.98 0.81 0.83 0.90 1.42 0.64 Sulphur % 0.15 0.15 14.86 0.15 0.09 0.12 0.11

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59 LIST OF REFERENCES Adam P, 1992. Australian Rainforests. Oxfo rd University Press, Melbourne, Australia. Aleric KM, and Kirkman KL, 2005. Growth and photosynthetic responses of the federally endangered shrub, Lindera melissifolia (Lauraceae), to varied light environments. American Journal of Botany 92: 682. Atwell BJ, Kriedmann PE, and Turnbull CGN, 1999. Plants in Action: Adaptation in Nature, Performance in Cultivation. Macmillan, Melbourne, Australia. Augspurger CK, 1984. Light requ irements of neotropical tr ee seedlings: a comparative study of growth and survival. Journal of Ecology 72: 777. Baur GN, 1964. The ecological basis of rain forest management. Forestry Commission of New South Wales, Sydney, Ne w South Wales, Australia. Baur, GN, 1989. Notes on the silviculture of major N.S.W. rainforest types. Forestry Commission of New South Wales, S ydney, New South Wales, Australia.. Baur GN, 1991. Rainforests of New South Wales. In: McKinnell FH, Hopkins ER and Fox JED (eds), Forest Management in Aust ralia. Surrey Beatty and Sons, Chipping Norton, NSW, Australia, pp .241. Bazzaz FA, 1996. Plants in Changing Envir onments: Linking Physiological, Population, and Community Ecology. Cambridge Univ ersity Press, Cambridge, MA, USA. Beaudet M and Messier C, 1998. Growth a nd morphological responses of yellow birch, sugar maple, and beech seedlings growing under a natural light gradient. Canadian Journal of Forest Research 28: 1007. Big Scrub Rainforest Landcare Group, 1998. Subtropical rainfore st restoration: A practical manual for landowners on ca ring for subtropical remnants and establishing rainforest plantings. Bi g Scrub Landcare Group, Mullumbimby, NSW, Australia. Bloom AJ, Chapin FS and Mooney HA, 1985. Resource limitation in plants: An economic analogy. Annual Review of Ecology and Systematics 16: 363. Bloor JMG, 2003. Light responses of shade-tolera nt tropical forest tr ee species in northeast Queensland, a comparison of forest and shadehouse grown seedlings. Journal of Tropical Ecology 19: 77.

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60 Bloor JMG and Grubb PJ, 2004. Morphological pl asticity of shadetolerant tropical rainforest tree seedlings exposed to li ght changes. Functional Ecology 18: 337 348. Boardman NK, 1977. Comparative photosynthe sis of sun and shade plants. Annual Review of Plant Physiology 28: 355. Bowman DM, 2000. Australian Rainforests: Is lands of Green in the Land of Fire. Cambridge University Press, Cambridge, UK. Brokaw NVL, 1987. Gap-phase regeneration of three pioneer tree sp ecies in a tropical forest. Journal of Ecology 75:9. Caldwell MM and Pearcy RW (eds.), 1994. Exploitation of Environmental Heterogeniety by Plants: Ecophysiological Processes Above and Below Ground. Academic Press, San Diego, CA, USA. Cameron DM and Jermyl D, 1991. Review of plantation performance of high value rainforest tree species. CSIRO Divisi on of Forestry and Queensland Forest Service, Brisbane, Queensland, Australia. Chazdon RL, 1988. Sunflecks and their impor tance to forest understory plants. Advances in Ecologica l Research 18: 1. Chazdon RL, 1992. Photosynthetic plasticity of two rainforest shrubs across natural gap transects. Oecologia 92: 586. Chazdon RL and Kaufmann S, 1993. Plasticity of leaf anatomy of two rainforest shrubs in relation to photosynthetic light acc limation. Functional Ecology 7: 385. Chazdon RL, Pearcy RW, Lee DW and Fetche r N, 1996. Photosynthetic responses of tropical forest plants to contrasting light environmen ts. In: Mulkey SS, Chazdon RL, and Smith AP, eds. Tropical Forest Plant Ecophysiology. New York, USA: Chapman and Hall, 5. Clark DA and Clark DB, 1992. Life history diversity of cano py and emergent trees in a neotropical rain forest. Ecological Monographs 62: 315. Condit R, Hubbell SP and Foster RB, 1995. Mort ality rates of 205 ne otropical tree and shrub species and the impact of severe drought. Ecological Monographs 65 (4): 419. Connell JH, 1970. On the role of natural enemies in preventing competitive exclusion in some marine animals and in rain forest trees. In: der Boer P.J., Gradwelleds and G.R. (eds), Proceedings of Advanced St udy Institute on Dynamics of Numbers in Populations. Center Ag. Publishi ng and Documentation, Wageningen, pp. 298 312.

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67 Walters MB and Reich PB, 1996. Are shade tolerance, survival, and growth linked? Low light and nitrogen effects on hardwood seedlings. Ecology 77: 841. Walters MB and Reich PB, 1999. Low-light car bon balance and shad e tolerance in the seedlings of woody plants: do winter deci duous and broad-leaved evergreen species differ? New P hytologist 143: 143. Walters MB and Reich PB, 2000. Seed size, ni trogen supply and growth rate affect tree seedling survival in deep shade. Ecology 81: 1887. Wayne PM and Bazzaz FA, 1993. Birch seedling reponses to daily time courses of light in experimental forest gaps and shadehouses. Ecology 74: 1500. Webb LJ and Tracey JG., 1981. Australian rainfore sts: patterns and change. In Keast A, ed. Ecological Biogeography in Australia, Junk, The Hague. Webb LJ and Tracey JG, 1994. The rainforest s of northern Australia. In: Australian Vegetation. Ed. RH Groves, pp 467. Camb ridge University Press, Cambridge, UK. Whitmore TC, 1983. Secondary succession from seed in tropical rainforest. Forestry Abstract 44: 767. Whitmore TC, 1990. An Introduction to Tropical Rainforests. Blackwell, London, UK. Whitmore TC, 1996. A review of some aspects of tropical rain fore st seedling ecology with suggestion for further inquiry. In Swaine, MD (ed.). Ecology of Tropical Forest Tree Seedlings, UNESCO /Parthenon, Paris/Carnforth. Yates DJ, Unwin Gl and Doley D, 1988. Rain forest environment and physiology. Proc Ecol Soc Aust 15: 31. Zipperlen SW and Press MC, 1996. Photosynthe sis in relation to growth and seedling ecology of two dipterocarp rainforest tree species. Journal of Ecology 84: 863.

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68 BIOGRAPHICAL SKETCH Jeffrey W. Kelly was born in Orlando, Fl orida, during the d ecadent s. He moved to Salt Lake City at the age of one, whereupon he spent the first third of his life planning an escape from the confines of th e renowned conservative mecca of SLC. To hasten an escape, he diligen tly worked to receive a Bach elor of Science degree in Forestry from Utah State University. Followi ng his studies at Utah State University, Jeff contacted Dr. Shibu Jose at the University of Florida to inquire about potential research opportunities. Dr. Jose spoke of an opportunity to research rainforest restoration in Australia, which sparked quite the interest and led to the beginning of a wonderful experience researching Australian rainforests. Jeff is currently working with the Pacific Northwest Fire Sciences Laboratory of the U.S. Forest Service in Seattle, Washington.


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GROWTH AND PHOTOSYNTHETIC RESPONSES OF AUSTRALIAN
SUBTROPICAL RAINFOREST SPECIES TO VARIABLE LIGHT ENVIRONMENTS:
IMPLICATIONS FOR RESTORATION AND MIXED-SPECIES PLANTATIONS













By

JEFFREY W. KELLY


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE

UNIVERSITY OF FLORIDA


2006






























Copyright 2006

by

Jeffrey W. Kelly

































To Harrison Shaw Kelly, Harry Erik Grass, and Everett Ruess















ACKNOWLEDGMENTS

I would like to thank my advisor and committee chair, Dr. Shibu Jose, for his

numerous ideas and financial support throughout my research. I would like to express

my gratitude to my committee members Dr. Debbie Miller, Dr. Rick Williams, and Dr.

Doland Nichols for their gracious assistance and valuable insight. I would also like to

thank Peter Bligh-Jones for invaluable assistance during my time in Australia, and thanks

go out to Mila Bristow for setting the experiment on the right track.

I would like to sincerely thank my parents for their constant benevolence and

support during my academic career. I am forever indebted to you both for showing me

the wonders of the natural world.

I wish to thank Erin Maehr for being such ajoy-bringer and wonderful presence in

my life. I would also like to thank my good friends from Gainesville, Eric Holzmueller,

Robin Collins, and Ped Daneshgar, for providing frequent and well needed non-academic

pursuits, to counteract the occasional academic malaise. Finally, I would like to thank

some wonderful friends from SLC, Brad Larsen, Jake MacFarlane and Joe and Janica

Hayes, for proving that true friendship can survive great distances and tumultuous events.
















TABLE OF CONTENTS

page

A C K N O W L E D G M E N T S ................................................................................................. iv

LIST OF TABLES ............. ..... ........................ ............. ............ vii

LIST OF FIGURES ............. .. ..... ...... ........ ....... .......................... viii

ABSTRACT .............. ......................................... ix

CHAPTER

1 IN TR OD U CTION ............................................... .. ......................... ..

Ecophysiology ........................................ ...............
Physiological R response to Light ............................................ .......................... 3
L e a f L ev e l .................................................................................. 3
W hole Plant Level ........................ ......... ... ......... .......... .... ....
Successional G radient............ ...... .......................................................... ........ .. ... ...
H history of A ustralian R ainforest.. ..................................................................... ........ 9
History of Subtropical Rainforest in New South Wales ..........................................10
R ainforest C haracteristics......................................................... ............... 12
S tu d y S p e c ie s ................................................................................................. 1 3
O objectives and H ypotheses........................................................................... .... 14
O b je ctiv e 1 ....................................................................... 1 5
O bjectiv e 2 ......................................................................................... 15

2 GROWTH AND PHOTOSYNTHETIC RESPONSES OF SIX AUSTRALIAN
SUBTROPICAL RAINFOREST TREE SPECIES TO A LIGHT GRADIENT....... 16

Introduction .......................................................................................................16
M e th o d s ..............................................................................2 1
Study Site............................................. 21
Study Species.................................................... 2 1
Shadehouse Experim ent .............................................. ............... 21
Photosynthetic G as Exchange ....................................................... 22
G row th A analysis .................................................. 23
N utrient Content .............................................................................. 23
Statistical A naly sis ...........................................................24
R e su lts ...........................................................................................2 4


v









Photosynthetic R response ......................................................... ............. 24
G row th Patterns ......................................................... .. ............ 25
D isc u ssio n ............................................................................................................. 2 6

3 POTENTIAL FOR SUBTROPICAL RAINFOREST RESTORATION ON
ABANDONED AGRICULTURAL LANDS IN NEW SOUTH WALES,
A U S T R A L IA ................................................... ................ ... 3 8

Introduction .............. ....... .............. ...... .... .......... ............ 38
M materials and M methods ....................................................................... ..................40
S tu dy S ite ........................................................................4 0
Species ............... ..... ......... ............ ............................40
Photosynthetic G as Exchange ........................................ ......... ............... 41
N utrient C content .................. ..................................... .. .. ........ .... 41
Statistical A naly sis ........................ ................ .. .. .... ........... 42
R e su lts ...........................................................................................4 2
D isc u ssio n ............................................................................................................. 4 3

4 SUMMARY AND CONCLUSIONS.......................................................................53

APPENDIX NUTRIENT CONCENTRATION.............................. ............57

L IST O F R E F E R E N C E S ........................................................................ .....................59

B IO G R A PH IC A L SK E TCH ..................................................................... ..................68















LIST OF TABLES


Table page

2-1 Life-history data for the study species ........................................ ......................31

2-2 Total dry biomass production (g), relative growth rate between 0 to 96 days
(RGR, mg g-1 d-1), specific leaf area (SLA, cm2 g-1), leaf mass ratio (LMR),
stem mass ratio (SMR), root mass ratio (RMR), total stem height (cm), and total
stem diameter (mm) shown by the six species at 96 days of growth under high
light (HL-60%), medium light (ML-30%), and low light (LL-10%) ...............32

2-3 Leaf-level photosynthetic parameters: Light saturated rate of photosynthesis
(Amax, [tmol CO2 m-2 s-1), apparent quantum yield (Aqe, ([tmol CO2 m-2 s-
1)/(tmol m-2 s-1)), and light compensation point (LCP, [tmol m-2 s-1) shown
by the six species grown under high light (HL 60% full sunlight), medium
light (ML 30% full sunlight), and low light (LL 10% full sunlight) ..............33

3-1 Life-history data for the study species ...................................................... ...47

3-2 Leaf-level photosynthetic parameters: Light saturated rate of photosynthesis
(Amax, tmol CO2 -2 s1), apparent quantum yield (Aqe, (tmol CO2 -2 -)/(tmol
m-2 S-1)), and light compensation point (LCP, rmol m-2 s-1) shown by the seven
species grown under 75% full sunlight. ...................................... ..................47

A-1 Total nutrient concentration in leaves of six subtropical rainforest species grown
under HL (60%), ML (30%) and LL (10%) full sunlight .......................................57

A-2 Total nutrient concentration in leaves of seven subtropical rainforest species
grown under 75% full sunlight .............. ......... ........................... .......... 58















LIST OF FIGURES


Figure page

2-1 Relative growth rate (mean (SE)) of seedlings of six Australian subtropical
rainforest trees, grown at 60%, 30%, and 10% of full sunlight .............................34

2-2 A) Diameter growth in (mm) and B) height growth in (cm) (mean (SE)) of
seedlings of six Australian subtropical rainforest trees grown at 60%, 30%, and
10% full sunlight .................................................................. ..........35

2-3 Light response curve of photosynthesis as a function of PPFD for A)
Elaeocarpus grandis, B) Flindersia schottiana and C) Gmelina leichhardtii
grown under three light treatm ents..................................................................... 36

2-4 Light response curve of photosynthesis as a function of PPFD for A) Flindersia
brayleyana, B) Heritiera trifoliolatum and C) Cryptocarya erythroxylon grown
under three light treatm ents........................................................ .............. 37

3-1 A) Diameter growth (m) and B) height growth (m) (mean (+/- SE)) of
seedlings of seven Australian subtropical rainforest trees at 3 years, grown under
75% full sunlight .................................... .............................. ........48

3-2 Stem Volume Index (SVI) (m3) (mean (+/- SE)) of seedlings of seven Australian
subtropical rainforest trees at 3 years, grown under 75% full sunlight ..................49

3-3 Light response curve of photosynthesis as a function of PPFD for A)
Elaeocarpus grandis, B) Flindersia schottiana and C) Gmelina leichhardtii
grown under 75% full sunlight ........... ..... ............................... 50

3-4 Light response curve of photosynthesis as a function of PPFD for A) Flindersia
brayleyana and B) Lophostemom confertus grown under 75% full sunlight..........51

3-5 Light response curve of photosynthesis as a function of PPFD for A)
Castanospermum australe and B) Heritiera trifoliolatum grown under 75% full
su n lig h t .................................................... .................... ................ 5 2















Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science

GROWTH AND PHOTOSYNTHETIC RESPONSES OF AUSTRALIAN
SUBTROPICAL RAINFOREST SPECIES TO VARIABLE LIGHT ENVIRONMENTS:
IMPLICATIONS FOR RESTORATION AND MIXED-SPECIES PLANTATIONS

By

Jeffrey W. Kelly

August 2006

Chair: Shibu Jose
Major Department: School of Forest Resources and Conservation

Growth, biomass distribution, and net photosynthesis were measured for seedlings

of six Australian subtropical rainforest tree species in a shadehouse experiment consisting

of three artificial light environments (10%, 30%, and 60% full sunlight) in order to

determine ecophysiological variability to light environment. A field study utilizing

natural light (75% full sunlight) complemented the shadehouse experiment. An

understanding of growth and photosynthetic potential of subtropical rainforest species in

relation to variations in light environment can be useful for determining the sequence of

species introductions in rainforest restoration projects and mixed species plantations.

Morphological responses followed the typical sun shade dichotomy, with early and

late secondary species (Elaeocarpus grandis, Flindersia brayleyana, Flindersia

schottiana, and Gmelina leichhardtii) displaying a higher relative growth rate (RGR)

compared to mature stage species (Cryptocarya erythroxylon and Heritiera trifoliolatum).

Based on the shadehouse study, physiological responses provided limited evidence of a









distinct dichotomy between early and late successional species. E. grandis provided a

clear representation of an early successional species, with marked increase in Amax in

high light and an ability to down regulate photosynthetic machinery in low light

conditions. The remaining species (F. brayleyana, F. schottiana, G. leichhardtii, and H.

trifoliolatum) were better represented as falling along a shade-tolerant continuum, with

limited ability to adjust physiologically to an increase or decrease in light, maintaining

similar Amax across all light environments.

Results show that most species belong to a shade-tolerant constituency, with an

ability to grow and persist across a wide range of light environments. Growth and

photosynthetic performance of most species reached a maximum in 30% to 60% of full

sunlight found in shadehouse conditions. All species under natural conditions displayed

an ability to acclimate to heightened light conditions, reaching their highest Amax in 75%

full sunlight. Results indicate that the study species offer a wide range of potential

planting scenarios and silvicultural options, with ample potential to achieve rapid canopy

closure and restoration goals.














CHAPTER 1
INTRODUCTION

During the later part of the 1980s, nearly all timber extraction from state owned

subtropical and tropical rainforest within New South Wales and Queensland ceased,

corresponding to the inclusion of these forests for listing on the World Heritage register

(Erskine et al. 2005). An impetus for World Heritage listing was the continual removal

of timber, on state owned lands, above an annual sustainable level and with limited

understanding of the requirements necessary for rainforest regeneration (Baur 1989).

Prior to the listing of rainforest remnants on the World Heritage register and the

subsequent change in rainforest management, very little research was conducted to

determine regeneration or silvicultural strategies for management of rainforest species.

Experiments with growing subtropical and tropical rainforest timber in plantation settings

during the early part of the 1900s showed little promise, as a result of limited information

or understanding available concerning the silvicultural and management requirements for

subtropical and tropical Australian rainforest species (Erskine et al. 2005). As the native

subtropical and tropical rainforest element met the economic and resource needs of the

timber industry for the duration of the 19th century, the necessity to further understanding

of the silvicultural and management requirements of rainforest species remained minute.

With inclusion of state-owned subtropical and tropical rainforest within New South

Wales and Queensland on the World Heritage register the imperative for furthering the

knowledge base concerning rainforest species developed. Such a prerogative developed

with its basis centered on the continued demand for rainforest cabinet timbers (Glengross









and Nichols 2005), the potential of cabinet timbers as plantation species (Cameron and

Jermyl 1991; Russel et al. 1993; Herbohn et al. 1996) and the position of Australia, as

one of the wealthiest nations with rainforest, to provide an example of sustainable

management of the rainforest resource (Adam 1992). The movement into sustainable

management of rainforest timbers carries with it some broad necessities for successful

implementation, such as understanding the regeneration requirements of rainforest

species, developing silvicultural methods for managing desired species, and acquiring

information about the ecophysiological variability of subtropical and tropical rainforest

species.

Ecophysiology

Plant ecophysiology is the science of understanding how plants respond to abiotic

and biotic factors that affect their growth and development in a given environment

(Larcher 2003). Ecophysiological research assists in determining how and why species

grow well under certain conditions and elucidating the factors that limit their growth such

as resource competition for water, light, or nutrients. This field of research provides an

understanding of whole plant functions while also providing insight into forest health

particularly through identifying stressful environments to plant growth. One of the most

pertinent facets to forestry, of ecophysiological research, is a determination of growth and

performance of tree species. In conducting ecophysiological research, a prime method

for elucidating growth and performance of plant species is to select a suite of

environmental variables and evaluate the response of species to the range of

environmental variables selected. A major emphasis of ecophysiological research has

been the relationship between sunlight and plant function, distribution, and growth

(Chazdon et al. 1996). Sunlight presents a pervasive and omnipresent resource which









distributes copious supplies of energy to terrestrial ecosystems, thereby directly

influencing the global distribution and general behavior of plant species (Atwell et al.

1999).

Physiological Response to Light

Light is one of the most integral environmental variables influencing the growth

and distribution of plant species (Boardman 1977; Lambers et al. 1998). Growth,

performance, and survival of tree seedlings and saplings within forested ecosystems are

guided by the amount of light available at a given site (Denslow 1980, 1987; Chazdon

1988; Caldwell and Pearcy 1994). Low-light levels may strain plants by limiting

photosynthesis, leading to reduced carbon gain and reduced growth. Conversely, high

levels of light can lead to photoinhibition, resulting in damage to the photosynthetic

apparatus (Lambers et al. 1998). Under high radiation loads plant species may also suffer

from increased water loss through higher transpiration rates (Lambers et al. 1998). To

account for variability of the light environment, species have developed strategies to cope

with environmental stresses from changes at the leaf-level through morphological and

physiological acclimation to changes at the whole plant level with adjustments to biomass

distribution and crown architecture (Kitajima 1994; Sipe and Bazzaz 1994; Poorter 1999;

Jose et al. 2003).

Leaf Level

Acclimation of morphological and physiological traits of seedling foliage has been

well documented for both early (light-demanding) and late (shade-tolerant) successional

species (Oberhauer and Strain 1984; Pearcy 1987; Strauss-Debendetti and Bazzaz 1991;

Tumbull et al. 1993; Kitajima 1994). Early successional (light-demanding) species are

found to be more plastic in their response to environmental change than late successional









(shade-tolerant) species (Strauss-Debendetti and Bazzaz 1991, 1996; Bazzaz 1996).

Plasticity or ability to react to a change in the environment, of early successional species

operates through photosynthetic characteristics and morphological change (Lambers et al.

1998). In most cases, photosynthetic rate per unit leaf area is greater for pioneer, light-

demanding species (Walters et al. 1993; Kitajima 1994; Reich et al. 1995). Moving

between light intensities, shade-tolerant species display lower variability in

photosynthetic responses when grown under different irradiances than do light-

demanding species (Strauss-Debendetti and Bazzaz 1996; Valladares 2000). Limited

response by shade-tolerant species reflects an inability to increase electron transport,

carboxylation capacity, and stomatal conductance (Chazdon et al. 1996). In contrast, the

inherently high photosynthetic capacity of light-demanding species provides a built in

mechanism for altering photosynthetic properties (Chazdon 1992), exhibited through a

down-regulation of electron transport and carboxylation capacity in response to a low

light environment (Chazdon et al. 1996). Successional status of trees is also determined

by a suite of ecophysiological, morphological and demographic traits in relation to

fluctuations in available resources (Mulkey et al. 1993); thus it follows that rates of

photosynthesis and respiration are not the only factors determining a species successional

status.

Morphological variability emerges when looking at specific leaf area (SLA), the

ratio of leaf area to leaf mass, with light-demanding species displaying more variability in

SLA than shade-tolerant species in altered light environments (Walters and Reich 1999).

Shade-tolerant species growing in understory, low light conditions generally display a

high SLA, a response providing greater surface area to increase interception of light









(Atwell et al. 1999; Henderson and Jose 2005). In contrast, light-demanding species

growing in high light conditions generally develop low SLA values, correlating to

smaller, thicker leaves with greater palisade tissue layers (Lambers et al. 1998). The

reason for the variance in SLA is likely the result of evolutionary features which lead to

survivorship in shade. For shade-tolerant species, a low SLA is associated with long

lived, tough, and herbivore resistant leaves, all factors conferring a competitive advantage

to shade-tolerant species in low light (Reich et al. 1991; Kitajima 1994). Conversely,

light-demanding species exhibit leaves with a short lifespan, limited resistance to pests or

pathogens, and high turnover rates; all factors proving advantageous in environments

where resources are not limited (Lambers et al. 1998).

Whole Plant Level

Acclimation to high light at the whole plant level involves adjusting relative growth

rate (RGR), biomass allocation, and altering canopy architecture and crown morphology.

RGR, the rate of mass increase per unit mass present, is generally much greater for light-

demanding than shade-tolerant species in high resource environments while the variation

between shade-tolerant and light-demanding species in low resource environments is

generally minute (Lambers et al. 1998). In low resource (light) environments, shade-

tolerant species maintain similar RGR to light-demanding species through variation in

allocation and leaf morphology, a scenario which leads to maximizing the capture of the

growth limiting resource of light (Lambers et al. 1998). Differences in biomass allocation

to leaves, stems, and roots represent strategies for energy capture, spatial exploration, and

water and nutrient absorption (Grimel979; Tilman 1988). In low light or shaded

environments, shoot growth takes priority, while in strong light the antecedence is to root

growth (Atwell et al. 1999). In response to shade, light-demanding species generally









display an increase in stem elongation (Lambers et al. 1998), while shade-tolerant species

display much less plasticity, again likely as a result of evolutionary features selecting for

defense over faster growth rates in low light (Kitajima 1994). In shaded environments,

species generally distribute more biomass to leaves, creating a greater leaf area per unit

plant mass (Popma and Bongers 1988; Osunkoya 1994). Species growing in high light,

on the other hand, generally distribute a greater percentage of biomass to roots,

compensating for higher transpiration loss occurring with increased radiation loads. Thus

the response of plants to the environment is based on the search for components of

growth, as plants responding to shade increase biomass to leaves in order to access light

and plants growing in high resource (light) environments allocate relatively more

biomass to roots in order to better capture the limited resources of water and nutrients.

Changes in canopy architecture represent the search for limiting resources, with

light-demanding species grown in low light allocating more carbon to height growth and

shade-tolerant species grown in low light distributing more resources to the growth of a

few long branches (Zipperlen and Press 1996). Tree crown development of light-

demanding and shade-tolerant species follows two disparate paths based on preferred

light environments. Light-demanding species growing in high light typically display

deep, multilayered crown forms, with leaves scattered throughout the crown. Whereas,

shade-tolerant species growing in low light typically contain shallow, mono-layered

crowns, with a single layer of leaves at the periphery (Horn 1971; Poorter and Werger

1999).

Successional Gradient

Light in forests is very dynamic, often varying more dramatically than any other

single plant resource (Chazdon et al. 1996), and species separate themselves not only









based upon their divergent light requirements but also upon their varied acclimation

potentials (Valladares et al. 2002). From an ecophysiological viewpoint, species may be

divided into two distinct groups of light-demanding and shade-tolerant (Swaine and

Whitmore 1988). Light-demanding or gap requiring species produce numerous small

seeds, germinate in treefall light gaps, have high mortality rates, are shade intolerant and

grow rapidly, while shade-tolerant species produce a small number of large seeds,

germinate, develop, and display high survivorship in deep shade (Condit et al. 1995;

Chazdon et al. 1996; Strauss-Debenedetti and Bazzaz 1996; Press et al. 1996; Whitmore

1996). The trend for capturing resources is widely divergent between light-demanding

and shade-tolerant species. Light-demanding species exhibit high potential rates of

resource capture and growth, providing a built in mechanism for rapid growth and thus

competitive advantage in high resource environments. Conversely, shade-tolerant

species display adaptations to low light environments with much lower potentials for

resource capture, maintaining an advantage through persistence and defense (Kitajima

1994).

It has been suggested that species coexist through partitioning of the light resource,

optimizing performance based on specific light requirements (Denslow 1987).

Partitioning of the light resource occurs in one of two ways. The first avenue emphasizes

that species specialize to one end of the environmental gradient (light-demanding or

shade-tolerant), while the second path represents an alteration of a particular species

phenotype, or inherent range of change, to the light currently available at a particular site

(Valladares 1999, 2000). Light-demanding and shade-tolerant labels represent endpoints

of a continuum of responses to light (Osunkoya 1994; Poorter 1999). As such, the









phenotypic response to an alteration of the light environment may often provide greater

insight towards a species successional standing, or assist in developing an understanding

of tree species acclimation potential to changing light environments.

The usefulness of simplifying into a light-demanding/ shade-tolerant dichotomy is

that characteristics associated with each particular group may be utilized to manage tree

species as part of a resource management plan. The general pattern of forest

development following logging operations depends upon the relative abundance of tree

species occupying the opposite ends of the pioneer-climax successional dichotomy

(Swaine and Whitmore 1988). Pioneers depend upon open canopy conditions to facilitate

germination of an abundant soil seed bank, while climax species operate through rapid

growth of seedlings and saplings present at time of understory release created by large

openings in the forest canopy (Dalling et al. 1998; Dekker and de Graaf 2003). In open

conditions such as cleared forest land and land abandoned from agrarian uses, the

situation becomes more complex, as the relative abundance of species of either

successional stage is markedly reduced and often nonexistent. Adding to the complexity,

for those involved in restoration, is the relatively miniscule information available

concerning species regeneration dynamics and potential pathways of redevelopment.

To mitigate complexity requires the development of information pertinent to

rainforest restoration, such as determining species tolerance to a range of light conditions.

Measuring photosynthetic and morphological responses can provide greater

understanding of a species tolerance and growth to a range of light conditions and has

been successfully used in forestry, agriculture, horticulture, and ecology (Boardman,

1977; Walters et al.1993; Walters and Reich 1996). Successful restoration of rainforest









within Australia will depend upon a thorough understanding of tree species response to

limiting environmental variables such as water, nutrients and light, along with the

formulation of functional silvicultural and regeneration strategies to enable sustainable

and long-term management of the rainforest resource. In this project we will attempt to

address the physiological and morphological responses of six subtropical rainforest trees

to the light environment and elucidate the forest management opportunities where this

information would be most beneficial.

History of Australian Rainforest

The total area of rainforest in Australia stands at approximately 2 million hectares

(Webb and Tracey 1981). Two hundred years ago, the area containing rainforest may

have been four times as large (Floyd 1990). The history of Australian rainforest

landscape encompasses massive reduction in rainforest, resulting from the development

of an export market in Red Cedar, creation of an agrarian society, and resource extraction

beyond sustainable levels. An initial and very important export product to the earliest

European settlers was Toona australis-Red Cedar. Expansion in the search for Red

Cedar directed early settlement patterns, beginning near Sydney and progressing

northwards as supplies of timber dwindled (Adam 1992). Cedar-getting irrefutably

resulted in significant reduction of rainforest stands; although the greater impact

attributed to cedar-getting was identification of rainforest stands which were

consequently cleared to make way for agriculture and dairying (Adam 1992).

Clearing of land for agrarian purposes led to profligate destruction of rainforest,

leading to an almost 75% reduction of the original rainforest existing prior to European

settlement (Baur 1991). A major impetus for rainforest reduction was passage of the

Land Settlement Act in 1860, which promoted settlement and an agricultural focus,









leading to a bucolic relationship with the land and moving settlement away from the

nomadic lifestyle of the cedar-getters. Clearing for agrarian purposes occurred in all

rainforest areas along the east coast due to an inferred association of lush, verdant

rainforest vegetation with high soil fertility and grand agricultural potential. Only rarely

did this association hold as the clearing process led to a substantial loss of nutrients and

as a result limited productivity. Rainforest lands not cleared for agrarian purposes faced

selective logging of commercially viable species, conversion to single species

plantations, and conversion of low productivity rainforest to Eucalypt plantations (Adam

1992).

History of Subtropical Rainforest in New South Wales

The total area of rainforest within New South Wales stands at approximately

200,000 hectares (Floyd 1990), an enormous reduction from an estimated pre-settlement

value of 1,000,000 hectares (Baur 1991). In a region of New South Wales known as the

"Big Scrub", clearing for agriculture led to an even more prodigious reduction in

rainforest, from 75,000 hectares pre-settlement to less than 300 hectares today (Floyd

1990). Activities which led to extensive reduction of rainforest stands in New South

Wales approximate those conducted across the rest of the Australian continent, with

timber extraction and agrarian uses as the guiding forces in resource use.

The focus of forest management in New South Wales today displays little

resemblance to historical patterns focused on select species and the production of single

species plantations. The current trends in rainforest management include creation of

mixed species plantations, and enhanced research into regeneration requirements and

silvicultural techniques for management of rainforest species. A major catalyst for these

newly emerging activities is an abundance of cleared and under utilized rainforest lands









in various states of disrepair. Enormous potential exists to convert these areas back

towards rainforest through restoration activities or in the development of mixed species

plantations.

Management options for rainforest species on public land within New South Wales

excludes harvesting (Floyd 1990), resulting in an emphasis on preservation as national

parks and World Natural Heritage Areas or towards rainforest restoration on public and

private lands. Restoration activities are predicated on the development and maintenance

of self sustaining processes of forests towards a close approximation of their original

state. Restoration efforts generally seek rapid development of a canopy in order to

facilitate the subsequent domination of a site by rainforest trees in the shortest time

possible (Kooyman 1996). Thus a key consideration to limit costs is an understanding of

species regeneration strategies and general autecology in order to develop appropriate

planting and silvicultural strategies.

Mixed species plantations may serve as another viable alternative, especially when

faced with restoration of large scale areas or when costs associated with restoration

become excessive (Lamb 1998). Information pertinent to development of mixed species

plantations include the value of timber species and potential growth rates of selected

species (Glencross and Nichols, 2005). Efficient site utilization is a guiding principle of

mixed species plantations and can be achieved through appropriate spacing and

understanding successional attributes of utilized species (Keenan 1996). As with

restoration, the best management strategy for utilizing rainforest species is maintaining,

as a focal point, an understanding of the ecology of rainforest communities and their

regenerative and successional processes.









Rainforest Characteristics

Rainforests consist of broken fragments along the eastern coast of Australia,

conceptualized as an archipelago amongst a sea of fire-prone eucalypt and agricultural

lands (Bowman 2000). Once considered 'alien and invasive' to the Australian flora, it is

now understood that rainforest existed long before eucalypt and other sclerophyllous

vegetation (Webb and Tracey 1981). Distribution of rainforest lies over the entire

latitudinal range of Australia, which includes climates from cool-temperate to tropical.

These forests form a discontinuous distribution along the eastern fringe of Australia,

being restricted to areas characterized by an average annual rainfall greater than 1,300

mm and areas with low fire frequency (Specht and Specht 1999; Webb and Tracey 1994).

There are four sub-formations of rainforest within New South Wales (cool

temperate, warm temperate, subtropical, and dry), with distribution of each sub-formation

dependent upon six major factors (climate, topography, microclimate, soil, fire, and

competition) (Floyd 1989). Sub-tropical rainforest is the most well developed formation

with distinguishing features that include occupation of sites with richer volcanic and

alluvial soils (generally kraznosem soil (Isbell 1998)), rainfall in excess of 1300 mm

annually, and sheltered situations generally below 900 m in altitude (Floyd 1989).

Subtropical rainforest occurs in patches along the eastern coast from New South Wales to

the uplands of far north Queensland (Lat 36 S to Lat 17) (Floyd, 1989). Tree species of

this formation are conspicuously lofty, at 30-45 m height, typically with two to three

levels arranged in a staggered rather than an even canopy (Floyd 1990). Tree

composition of subtropical rainforest ranges from 10 to 60 species and rarely does a

single species dominate (Floyd 1989). Distinctiveness of this rainforest type arises

through plank buttressing of many tree species and resplendent, impenetrable canopies









covered with epiphytes and thick woody vines. Most species exhibit large compound

leaves, with entire leaves or leaflets more than 7.5 cm long (Floyd 1990).

Study Species

Five tree species native to New South Wales were selected for the study. A single

species native to Queensland was included due to its utilization in restoration work

throughout NSW. Species selection was based on presumed shade tolerance covering a

broad successional gradient from early secondary (light-demanding) to later secondary

and mature (shade-tolerant).

The six species selected for the study included: Cryptocarya erythroxylon -

Pigeonberry Ash, a mature stage species generally relegated to the second story in canopy

development and occasionally appearing in the first story, rarely developing as an

emergent species (Floyd 1989); Elaeocarpus grandis Silver Quandong, an early

secondary species occupying a wide range of sites and displaying a rapid growth habit

(Floyd 1989); Flindersia brayleyana Queensland Maple, an early to late secondary

species native to Queensland, which can tolerate a wide range of light conditions

(Thompson et al. 1988); Flindersia schottiana Bumpy Ash, an early secondary species

typically found in riverine and subtropical rainforest (Floyd 1989); Gmelina leichhardtii -

White Beech, a late secondary species which attains significant height dimensions and

grows on a wide range of sites (Floyd 1989); Heritiera trifoliolatum White Booyong, a

mature stage species which amasses large dimensions with prominent buttresses (Floyd

1989). All species are considered as particularly viable for restoration efforts and mixed

species plantations (Kooyman 1996; Big Scrub Rainforest Landcare Group 1998).

Few studies are available on the ecophysiological variability of subtropical

rainforest species. Those developed have generally focused upon species native to









Queensland, such as F. brayleyana (Thompson et al. 1988). An emphasis in this research

project was placed upon subtropical rainforest species native to northern New South

Wales. The general format of previous studies detailing growth (Thompson et al. 1988;

Osunkoya et al. 1993) and photosynthetic performance ofF. brayleyana (Thompson et al.

1988, 1992a, 1992 b; Swanborough et al. 1998) and H. trifoliolatum (Cunningham and

Read 2002) under a range of light and temperature conditions were closely approximated

for all species included in the current study. The background on F. brayleyana and H.

trifoliolatum was elementary in nature while information on the remaining 4 species was

decidedly less complete, with little known concerning growth and photosynthetic

performance of C. erythroxylon, E. grandis, F. schottiana, and G. leichhardtii.

Objectives and Hypotheses

Successful establishment of these species in restoration projects and mixed species

plantations requires detailed studies which evaluate their growth and physiological

response to environmental variability. Thus, the broad objective of the study was to

determine ecophysiological variability of the selected subtropical rainforest tree species.

A major focus of ecophysiological variability pertains to changes in physiology and

morphology of species to contrasting light environments. Thus, a thorough evaluation

would identify within and between species variation to the light environment in order to

ascertain regeneration dynamics and successional aspects of subtropical rainforest

species. In order to elaborate on species successional characteristics, the current study

evaluated rates of photosynthesis and measurements of growth and biomass allocation of

selected species under a range of light conditions, with the following two specific

objectives.









Objective 1

The first objective focused on physiological variability within and between species, with

a priority on the effect of light level on photosynthetic characteristics of each species.

The relevant hypotheses were:

* Hypothesis 1: Light-demanding (pioneer and early secondary) species will show
higher rates of photosynthesis in high-light environments compared with the shade-
tolerant (late secondary and mature) species.

* Hypothesis 2: Shade-tolerant (late secondary and mature) species will display a
narrower range of photosynthetic responses under three light environments than
light-demanding (pioneer and early secondary) species.

Objective 2

The second objective focused on morphological variability occurring within and

between species. Variables evaluated included growth and biomass allocation; focusing

on relative growth rate (RGR), specific leaf area (SLA) and nutrient content of selected

species. The relevant hypotheses were:

* Hypothesis 1: Light-demanding (pioneer and early secondary) species will achieve
a higher RGR in the high light environment compared with the shade-tolerant (late
secondary and mature) species.

* Hypothesis 2: Light-demanding species will achieve higher RGR in all light
environments than will shade-tolerant species.

* Hypothesis 3: Light-demanding species will display more variability in specific
leaf area (SLA) under the three light treatments than shade-tolerant (later secondary
and mature) species.

The results of shadehouse and field-based experiments conducted to test these

hypotheses will be presented over two succeeding chapters. In Chapter 4, a summary of

findings will be presented, followed by a discussion on the implications for management

of subtropical rainforest species for restoration and mixed species plantations.














CHAPTER 2
GROWTH AND PHOTOSYNTHETIC RESPONSES OF SIX AUSTRALIAN
SUBTROPICAL RAINFOREST TREE SPECIES TO A LIGHT GRADIENT

Introduction

Large areas of the world's forests have been lost or degraded and landscapes

everywhere are being simplified by current land-use practices (Lamb and Gilmour 2003).

In many parts of the world this pattern of loss and destruction is just beginning, while

elsewhere numerous countries are moving away from simplification of the landscape.

Throughout the brief history of European impact upon the Australian continent, sizable

areas of rainforest have been altered to satisfy resource needs. General patterns

associated with colonization and subsequent resource extraction greatly influenced the

loss and degradation of the Australian rainforest landscape. Today, land use practices are

moving away from simplification of the landscape into the complex and often uncharted

territory of landscape rehabilitation and rainforest restoration.

Early land use patterns in Australia were geared towards progressive clearing of

vast tracts of rainforest for agriculture, dairying, and timber (Adam 1992). An estimate

on the extent of rainforest clearing sets a pre-settlement figure at 8 million hectares

(Floyd 1990), while the area existing as rainforest today is estimated at 2 million hectares

(Webb and Tracey 1981). Abeyance of rainforest clearing, at least in state owned

rainforest lands, coincided with placement of Australian rainforest on the World Heritage

register (Erskine et al. 2005). The historical four fold reduction in areas consisting of

rainforest (Floyd 1990) has left much of the Australian landscape bereft of a rainforest









element. World Heritage listing assisted in conservation and preservation of existing

rainforest, but a vast expanse of potential rainforest land within Australia sits unattended,

either abandoned from agrarian uses or left degraded through exotic species or weed

invasion. Frequently, very large areas are in dire need of restoration and subsequent

initiation of sustainable management for long-term benefits to the landscape (Smith et al.

2005). Restoration has been enacted in many regions of New South Wales since the late

1980s, mainly to restore small parcels of rainforest onto land controlled by the NSW

National Parks and Wildlife Service. However, limited information concerning the

ecology of rainforest species has often led to mixed results regarding these restoration

efforts.

Restoration attempts in Australia are often hampered by a paucity of

ecophysiological data on rainforest species. Relevant information to ecophysiology

centers on perturbations in the environment and the resulting vicissitude of plant species.

Environmental perturbations, creating variation in the light environment, generally occur

as disturbance events such as fire, cyclones, disease, and insect damage (Kimmins 1987);

related vicissitude in plant structure and function modulate physiology and morphology

of plant species (Atwell et al. 1999). Restoration often faces a difficult task in perceiving

or parlaying environmental variation without the benefit of a baseline to compare with.

Such is often the circumstance in restoration when little if any of the original

environment exists. To mitigate the complexity associated with restoring nonexistent or

underrepresented ecosystems, current research seeks to determine baseline information of

species response to environmental variation. Of general concern is plant species response

to a range of light environments.









Measuring photosynthetic and morphological responses can provide a greater

understanding of species tolerance to and growth under a range of light conditions and

has been successfully used in forestry, agriculture, horticulture, and ecology (Boardman

1977; Walters et al. 1993; Walters and Reich 1996). Acquiring an understanding of

species growth and physiological performance leads to an enhanced opportunity to utilize

rainforest species in resource management activities (Chazdon et al. 1996). In many

silvicultural operations, an understanding of the ecophysiological and regeneration

requirements of key species serves as a unifying theme (Graaf 2000; Wadsworth 2001).

Restoration objectives generally center upon initiating successional development where

natural recovery is not underway and accelerating successional processes where it is

(Lamb 1998). Thus any restoration effort must involve an understanding of successional

processes and response of plant species to disturbance mechanisms.

Disturbance is widely regarded as a primary mechanism for maintaining the

diversity found in tropical and subtropical rainforests (Connell 1970, 1978; Connell et

al. 1984). Disturbance regimes are also important in the evolution of tree species life

history characteristics (Sheil and Van Heist 2000; Sheil and Burslem 2003).

Environmental volatility arriving from disturbance generally provides the impetus for

facilitation or exclusion of tree species. One of the causal mechanisms of the discrepancy

between rapid emergence and prolonged persistence is species response to sun or shade

conditions (Janzen and Vazquez-Yanes 1970; Hubbell 1979, 1998, 2001; Connell 1970,

1978; Connell et al. 1984).

Rainforest species are typically depicted as belonging to one of two broad guild

associations (Swaine and Whitmore 1988). Light-demanding or gap requiring species









germinate in treefall light gaps, have high mortality rates, are shade intolerant and grow

rapidly, while shade-tolerant species germinate, grow, and have high survivorship in deep

shade (Condit et al. 1995; Chazdon et al. 1996; Strauss-Debenedetti and Bazzaz 1996;

Press et al. 1996; Whitmore 1996). Acclimation of morphological and physiological

traits of seedling leaves has been well documented for both early (light-demanding) and

late (shade-tolerant) successional species (Oberhauer and Strain 1984; Pearcy 1987;

Strauss-Debendetti and Bazzaz 1991; Tumbull et al. 1993; Kitajima 1994).

Early successional (light-demanding) species are found to be more plastic in their

response to environmental change than late successional (shade-tolerant) species

(Strauss-Debendetti and Bazzaz 1991, 1996; Bazzaz 1996). For example, many

comparative studies have shown that seedlings of light-demanding species maximize

growth potential in low light by developing a high specific leaf area (SLA) and high leaf

area ratio (LAR) (Walters et al. 1993; Kitajima 1994). In addition they allocate more

resources to new growth, with limited provision to storage and defense (Augsburger

1984; Kobe 1997). Conversely, shade-tolerant species distribute very little to new

growth and instead allocate towards traits associated with persistence (Walters and Reich

1999), such as the production of dense, durable, well defended tissues (Augspurger 1984;

Kitajima 1994). As witnessed in numerous studies, the strategies of each guild are quite

disparate and as such provide a window into patterns and processes of forested systems.

The dynamics of regeneration are often inferred after determining the sun versus

shade characteristics of select species. Such a scenario serves as an elementary preview

of the initial processes accounting for facilitation or exclusion of tree species and may

provide a tool to predict future stand composition and structure following disturbance.









Disturbance events provide the appropriate environment for a given species and lead to

wide responses which govern tree diversity within the subtropical rainforest. An

understanding of forest processes that maintain biodiversity is crucial in conducting any

management intervention and likely the most important is the intensity and frequency of

disturbance events. Conducting forest management based on perceived response to

disturbance allows utilization of natural processes as the guide to appropriate resource

management. Such a blueprint towards imitating the ecology of forests creates an

allowance for using disturbance regimes as the primary tool for initiating and

perpetuating forest structure and function (Baur, 1964; Whitmore 1990; Shiel and van

Heist 2000). Therefore a key function of the current research was to determine the

response of species to alterations of the forest environment.

The broad objective of the current study was to elucidate the ecophysiological

response of six subtropical rainforest species to altered light environments. Such an

objective was a response to the growing interest in rainforest restoration and habitat

rehabilitation efforts. In an effort to facilitate restoration efforts, the specific objective

was to determine optimal light environments for growth of six subtropical rainforest tree

species, accomplished by comparing growth, morphological and photosynthetic

responses of plants under natural and controlled light environments. Two questions were

asked during this study: (1) What photosynthetic adjustments do the six species make to

different light environments? (2) Do morphology, growth, and biomass differ for

seedlings growing in varied light conditions?









Methods

Study Site

The shadehouse study was conducted on the campus of Southern Cross University,

Lismore in northeast New South Wales, Australia (Long 153.270 East 28.81 South).

The campus is situated in the subtropical rainforest region ofNSW, at an altitude of 11

meters. Rainfall in Lismore averages over 1300 mm per year, monthly measurements

during the study period were as follows: January (155.4 mm), February (183.6 mm),

March (188.4 mm), and April (129.2 mm). The average temperature during the study

period was (22.80C), with average temperatures for each month as follows: January

(24.40C), February (240C), March (22.70C), and April (200C).

Study Species

Six rainforest species were selected, based upon the regeneration stages they are

known to be associated with in a regenerating forest, including those that form part of the

mature forest (Floyd 1990; Kooyman 1996). Four main groups were recognized: pioneer,

early secondary, late secondary, and mature phase species (Table 2-1). Pioneer and early

secondary species are well suited to regenerate on disturbed and open sites, but are

characterized by a short life-span (Whitmore 1983; Swaine et al. 1987). Conversely, late

secondary and mature phase species are well suited to regenerate under shade, and may

live considerably longer (Whitmore 1983; Swaine et al. 1987). All species are

considered particularly viable for restoration and mixed species plantation work within

New South Wales (Kooyman 1996; Big Scrub Rainforest Landcare Group 1998).

Shadehouse Experiment

The experiment was conducted in a randomized complete block design with three

blocks (shadehouse). Seedlings were obtained from area nurseries, whereupon they were









transferred from small planting containers and repotted in 1 gallon pots using a 70%

standard potting mix (Yates General Purpose Potting Mix Australian Standard [Regular

Grade]) to 30% gravel and sand combination. Each block (shadehouse) corresponded to

one of three light treatments (60%, 30%, and 10% of full sunlight). The three light

treatments (60%, 30%, and 10% full sunlight) were created using neutral density shade

cloth.

Seedlings were watered to maintain field capacity, and all seedlings were fertilized

biweekly with Aquasol (Yates, Sydney, Australia) Fast Acting Soluble Fertilizer with

trace elements at a rate of 8 g to 5 L of water, applied to each seedling in 100 mL

amounts.

Photosynthetic Gas Exchange

Light response curves were measured on a leaf area basis with a LICOR-6400

portable photosynthesis system (Li-Cor, Inc., Lincoln, Nebraska USA) using the "LIGHT

CURVE" automatic program with an artificial red/blue LED light source. Measurements

were made at light levels of 2000, 1500, 1000, 500, 200, 100, 50, 20, and 0 [tmol m-2 s-

. The leaf chamber environment was maintained at the following: C02, 370 [tmol m-2.

s-1, and temperature, 26C. Photosynthetic measurements were made on 10 randomly

selected seedlings of each species from each light treatment. Photosynthetic

measurements were taken from 0700 to 1300 hours under clear to partly cloudy skies

(Mar. 05 Apr. 05) on the most recent fully expanded leaf. Prior to the start of each light

response curve each selected leaf was placed in the leaf chamber at 1500 [tmol m-2 s-1

for 5 minutes. The order of treatments and seedlings used were randomly selected each

day.









Growth Analysis

Relative growth rate (RGR; biomass growth per unit plant biomass, in mg g-1 day-1)

was calculated according to Hunt (1978). The determination of RGR for each species

required destructive sampling of three species from each treatment at the beginning (Jan.

05) and at the conclusion of the study (Apr. 05). Seedlings were separated into leaves,

stems and roots, and dried at 70C in a forced air oven for 48 h before quantifying dry

mass. Roots were carefully washed prior to drying. The calculation of relative growth

rates (RGR; Hunt 1982) were estimated as follows:

RGR = ln(W2) ln(W1)
At (days)
ln(W2) = April 2005 dry mass
ln(W1) = January 2005 dry mass
At (days) = 1/11/2005 to 4/17/2005 = 96 days

Leaf area was measured on a subset of leaves for each species in each light

treatment using a LI-COR LI-3000 leaf area meter (Li-Cor Inc., Lincoln, NE USA).

From the primary data, used to calculate RGR, the following variables were derived:

specific leaf area (SLA; leaf area/leaf mass, in cm2 g-1), leaf mass ratio (LMR; leaf

mass/total plant mass, in g g-1), stem mass ratio (SMR; stem + petiole mass/total plant

mass, in g g-1), and root mass ratio (RMR; root mass/total plant mass, in g g- ). These

variables represent leaf display (SLA), and biomass allocation (LMR, SMR, RMR).

Nutrient Content

A representative sample of leaves was gathered for all species in each treatment,

and analyzed by the Environmental Analysis Laboratory located on the campus of

Southern Cross University, Lismore, New South Wales, Australia. Samples were

combusted at 5500 C and digested with nitric acid to discern total nutrients.

Concentration of nitrogen was determined using a LECO CNS2000 Analyzer. Nutrient









analysis facilitated an evaluation of the relative proportion of specific nutrients (nitrogen,

phosphorous, potassium, and sulfur) of selected leaves from each treatment (Table A-1).

Statistical Analysis

Light curves were fitted by nonlinear regression using the Mitscherlich model

equation (Sigma Plot 9.0, SSPS Inc., Chicago, Illinois USA) (Potvin et al. 1990; Peek et

al. 2002; Aleric and Kirkman 2005):

A = Ama [1 e-Aqe(PPF-LCP)]

where Amax represents the asymptote of photosynthesis, Aqe corresponds to the initial

slope of the curve, PPF represents the incident photosynthetic photon flux, LCP denotes

the x intercept, where net photosynthesis is equal to 0, and A represents net

photosynthesis. This model was used to identify the following parameters: Amax, the light

saturated rate of photosynthesis, Aqe, the apparent quantum yield, and LCP, light

compensation point.

Morphological field data and photosynthetic plant responses were evaluated using a

two-way ANOVA, with light treatment and species as independent variables (SAS 9.0,

SAS Institute Inc., Cary, North Carolina USA). After ANOVA, differences among means

were tested by Tukey's multiple comparison test. Mean values for root mass ratio

(RMR), stem mass ratio (SMR), and leaf mass ratio (LMR) were calculated as the dry

mass of root, stem, and leaves divided by the total dry mass, averaged for all seedlings in

a treatment.

Results

Photosynthetic Response

Light saturated rates of photosynthesis (Amax) increased for all species from 10% to

30% full sunlight, but decreased for most species moving from 30 to 60% full sunlight









(F2,162=93.59, P < 0.0001)(Table 2-3, Figure 2-3 and 2-4). The two exceptions were

Elaeocarpus grandis and Flindersia brayleyana, both early secondary species, which

achieved highest Amax in the 60% full sunlight treatment. The apparent quantum yield

(Aqe) showed a significant difference within light treatment (F2,162=5.45, P < 0.05), with

mean values for most species greatest in the 60% full sunlight treatment and decreasing

with decreasing light levels. The exception was for F. brayleyana, which achieved peak

Aqe in the 10% full sunlight treatment. Light compensation point (LCP) for species in the

60% full sunlight treatment was significantly greater (LCP) than species in the 30 and

10% full sunlight treatments (F2,162=105.3, P < 0.001). An exception occurred with

Flindersia schottiana, which achieved the greatest LCP in the 30% full sunlight

treatment.

Growth Patterns

Stem diameter growth (Figure 2-2) for most species achieved a maximum in the

60% full sunlight treatment and decreased with decreasing light. The two exceptions

were the two mature stage species (Cryptocarya erythroxylon and Heritiera

trifoliolatum), which achieved peak stem diameter growth in the 30% full sunlight

treatment. Stem height growth (Figure 2-2) displayed a similar pattern with most species

achieving maximum height growth in the 60% full sunlight treatment, with the exception

being F. brayleyana and Gmelina leichhardtii, both of which displayed a peak in height

growth in the 30% full sunlight treatment.

Total plant dry biomass displayed a significant difference among light treatments

(F2,18=37.65, P < 0.0001), with most species displaying a drop in total plant dry biomass

when moving from 60% full sunlight to lower light levels. The only species displaying a









different result was C. erythroxylon, which displayed a peak in total plant dry biomass in

the 30% full sunlight treatment.

Relative growth rate differed between species (F5,18= 25.9, P < 0.0001) and light

treatments (F5,18= 37.41, P < 0.0001). For most species RGR (Table 2-2, Figure 2-1)

decreased when moving from 60% full sunlight to lower light levels, with only C.

erythroxylon, a mature stage species showing a peak in RGR at 30% full sunlight.

Early and late secondary species (E. grandis, F. brayleyana, F. schottiana, and G.

leichhardtii) displayed a significant difference in specific leaf area (SLA) within species

moving from high light to low light (F10,72 = 5.54, P < 0.0001). The two mature stage

species (C. erythroxylon, and H. trifoliolatum) did not differ in SLA in any of the light

environments.

Biomass allocation patterns displayed contrasting results compared to common sun

versus shade comparisons. Leaf mass ratio (LMR) displayed a significant difference

within light treatments (F2,18=7.53, P < 0.05), with most species allocating the greatest

LMR in 60% full sunlight treatment and displaying a drop in the 30% and 10% full

sunlight treatment. Root mass ratio (RMR), showed a significant difference among light

treatments (F2,18=5.0, P < 0.05), although it differed with LMR in that most species

allocated a greater proportion to roots in the 10% full sunlight treatment as opposed to the

30% and 60% full sunlight treatments.

Discussion

Light is generally the most limiting resource to plant growth within rainforests

(Yates et al. 1988). Therefore, the ability of plant species to acquire and utilize light is an

important determinant of their competitive ability (Chazdon et al. 1996). Differences in

responses to light availability involve correlative ecological and morphological









characteristics of the studied species. A wide array of physiological responses was

detected in the current study, corresponding to a light-demanding and shade-tolerant

continuum (Osunkoya 1994).

The physiological response observed for most species, to the three light

environments, followed similar patterns to those reported for other shade-tolerant species

(Oberbauer and Strain 1986; Tani et al. 2001; Aleric and Kirkman 2005). In general,

these studies have reported a response pattern of increasing Amax with increasing light up

to intermediate levels, followed by a decline in Amax at high light levels. Acclimation

responses of shade-tolerant species do not generally involve increasing photosynthetic

capacity on a leaf dry mass basis (Sims and Pearcy 1991; Chazdon and Kaufmann 1993).

In contrast, light-demanding species generally display a high capacity to modulate

photosynthetic capacity in response to decreased light availability (Chazdon 1992;

Tumbull et al. 1993). This was best exhibited in the current study by early secondary E.

grandis, which increased Amax from low to high light, achieving greatest Amax in the 60%

treatment. Whereas, species displaying greater shade tolerance displayed much less

physiological plasticity, with minute changes in Amax when moving from low to high light

treatments.

The ability, of a given species, to acclimate physiologically to altered light

environments does not always provide a clear distinction between light-demanding and

shade-tolerant species. Part of this may be explained by the fact that, except for true

pioneer species; virtually all forest species must be able to tolerate low light conditions,

at least during the early stages of their life history (Clark and Clark 1992). Therefore,









determining shade tolerance may depend to a greater extent on the morphological and

carbon allocation patterns of species growing under low light conditions (Kitajima 1994).

Study seedlings displayed the typical sun-shade morphological responses reported

in many other studies, with increased specific leaf area in low light, and enhanced relative

growth rates in high resource environments (Walters et al. 1993; Beaudet and Messier

1998; Sack and Grubb 2002). SLA followed general patterns for most species, with

seedlings grown in low light displaying greater SLA than seedlings grown in heightened

light environments. An exception to this pattern occurred with the two mature stage

species (C. erythroxylon and H. trifoliolatum), which displayed limited variability in SLA

under oscillating light conditions. This is consistent with a review by Walters and Reich

(1999) in which shade-tolerant species were shown to be less variable in SLA when

grown under contrasting light conditions. In contrast, the early secondary and late

secondary species (E. grandis, F. brayleyana, F. schottiana., and G. leichhardtii)

displayed marked contrasts in SLA between low and high light treatments.

RGR patterns, for most species, also displayed a typical sun versus shade scenario,

with high light grown plants exhibiting the highest RGR and low light grown plants

displaying the lowest RGR (Loach 1970). The reason for variation in RGR between

light-demanding and shade-tolerant species may be accounted for by SLA, with species

containing an inherent capacity for high SLA generally displaying a greater RGR

(Lambers and Poorter 1992; Reich et al. 1998). Seedlings within the current study

closely approximated the association of SLA and RGR, with species achieving the

highest RGR also displaying an increase in SLA under oscillating light conditions. In

contrast, C. erythroxylon, a mature stage species, displayed a limited ability to alter SLA









which corresponded to a reduction in RGR under variable light conditions. In many

previous studies a relationship between RGR and mortality has been identified, with

findings of a positive (Walters and Reich 2000) and a negative (Kitajima 1994)

relationship between survival in shade and RGR. In the current study, this pattern could

not be deduced as mortality did not occur during the 96 days of the study, which may be

related to the short length of the experiment or light levels which were not sufficiently

low enough to represent understory conditions (Sack and Grubb 2001).

Biomass allocation patterns displayed little variability for half of the six species,

based on light treatment. RMR varied in low light conditions for C. erythroxylon, F.

schottiana, and G. leichhardtii, with a peak for all species occurring in the 10% full

sunlight treatment. This may account for the significant drop-off in RGR in low light for

these species, as more resources were allocated to roots, a non limiting factor in low light

situations, rather than providing greater allocation to leaves and thus providing greater

potential for light capture (Popma and Bongers 1988; Osunkoya 1994). A similar pattern

in LMR occurred for these species in the high light environment, with a peak occurring

for all species in the 60% full sunlight treatment. An increase in LMR would likely

correlate to a reduction in biomass allocated towards root mass, thus limiting the potential

for greater water uptake under high radiation loads (Poorter 1999).

An inherent difficulty occurs when attempting to extrapolate results gathered from

controlled experiments to natural conditions. Plants grown in shadehouses rarely

experience the full complexity of the light environment within the forest, in respect to

spectral quality and sunflecks (Ellsworth and Reich 1992; Wayne and Bazzaz 1993;

Dalling et al. 1998; Bloor 2003). In addition, shadehouse conditions effectively exclude









all causes of natural seedling mortality, such as herbivore damage or suboptimal growing

seasons (Walters and Reich 2000). Nonetheless, shadehouse experiments have been

shown to provide similar results as field studies in terms of species rankings in growth

parameters (Bloor 2003). Therefore, understanding species response to sun versus shade

conditions can assist toward development of guidelines concerning the amount of canopy

cover necessary to create ideal growing conditions.

For most species included in the study, ideal growing conditions fall within the

range of 30 to 60% full sunlight. Thus initial stand development for these species follows

a range of amenable planting densities (trees/hectare), especially as a few species

included in the current study continued to show significant growth in 10% full sunlight.

For example, a successful planting scenario may entail planting early secondary E.

grandis and F. brayleyana in year one, followed by the introduction of early secondary F.

schottiana and late secondary G. leichhardtti several years later. A diversifying mix of

mature stage C. erythroxylon and H. trifoliolatum may follow at some much later date

when the measured light environment in the understory approximates 30% full sunlight

or less. Similarly, silvicultural manipulations of stand density in basal area (m2/hectare)

provide for a full range of options from canopy retention maintaining light conditions at

10% full sunlight and thereby assisting mature stage species or maintaining light

conditions near 60% full sunlight and benefiting F. brayleyana and G. leichhardtii. In

the case of E. grandis little canopy retention may be necessary as it appears to respond

well to light conditions at or greater than 60% full sunlight. The general results of this

study indicate promise for inclusion of study species in rainforest restoration activities

and in the development of mixed species plantations. Ascertaining a complete










understanding of species performance will require further research into characteristics

leading to species growth performance and those characteristics which provide for

maintenance, persistence, and storage (Kitajima 1994; Kobe 1997). In light of this,

further research should be conducted for subtropical rainforest species under natural

conditions to further elucidate the response of species to herbivores, pathogens, and

nutrient and water limitation.

Table 2-1. Life history data for the study species.
Max Max
height DBH
Species Symbol (m) (cm) Successional stage
Cryptocarya erythroxylon Ce 35 125 Mature
Elaeocarpus grandis Eg 35 200 Early secondary
Flindersia brayleyana Fb 40 250 Late secondary
Flindersia schottiana Fs 45 100 Early secondary
Gmelina leichhardtii GI 40 150 Late secondary
Heritiera trifoliolatum Ht 45 200 Mature
*Adapted from Floyd 1990 and Kooyman 1996.










Table 2-2. Total dry biomass production (g), relative growth rate between 0 to 96 days
(RGR, mg g-1 d-1), specific leaf area (SLA, cm2 g-1), leaf mass ratio (LMR),
stem mass ratio (SMR), root mass ratio (RMR), total stem height (cm), and
total stem diameter (mm) shown by the six species at 96 days of growth under
high light (HL 60%), medium light (ML 30%), and low light (LL -
10%). Species codes as given in Table 2-1. Small letters show significant
differences at P < 0.05 among treatments for each species, after ANOVA and
Tukey's multiple comparison test. Species arrangement is in increasing order
of RGR.


Species
GI Eg Fb Ht Fs Ce
Total Biomass
HL 36.02a 13.49a 5.10a 22.04a 16.29a 32.85b
ML 33.38a 9.49a 5.03a 19.43ab 14.42ab 41.24a
LL 16.61b 8.80a 3.05a 13.56b 8.56b 27.45b
RGR
HL 11.37ab 10.12" 7.17ab 6.04a 4.80ab (-)0.83a
ML 10.56a 6.66ab 5.29a 4.73ab 3.66a 1.54a
LL 3.29b 5.82b 0.79b 0.99b (-)1.83b (-)2.71b
SLA
HL 84.60 133.60 117.8b 100.5a 115.30 110.7a
ML 124.2b 192.7b 127.7b 122a 150.7b 111.8a
LL 185.5a 242a 176.7a 117.8a 184.3a 118.2a
LMR
HL 0.31a 0.37a 0.27a 0.21a 0.42a 0.35a
ML 0.24a 0.32a 0.31a 0.23a 0.35a 0.27a
LL 0.16ab 0.37a 0.29a 0.23a 0.28ab 0.24ab
SMR
HL 0.37a 0.27a 0.32a 0.37a 0.32a 0.38a
ML 0.41a 0.30a 0.32a 0.34a 0.33a 0.36a
LL 0.37a 0.27a 0.36a 0.34a 0.35a 0.40a
RMR
HL 0.33ab 0.37a 0.42a 0.42a 0.26b 0.28b
ML 0.36b 0.39a 0.38a 0.43a 0.33ab 0.39ab
LL 0.47a 0.37a 0.35a 0.43a 0.38a 0.37a
Diameter Growth
HL 2.64a 2.47a 1.55a 2.21b 2.11a 2.10a
ML 2.29a 2.46a 1.47a 2.48a 1.88a 2.29a
LL 1.12b 2.12a 0.90a 0.97b 1.47a 1.59a
Height Growth
HL 10.72b 23.56a 4.73a 21.41a 7.54a 5.69a
ML 19.21a 14.81b 4.83a 16.37a 5.01a 5.21a
LL 12.26b 17.18b 4.06a 9.21b 5.43a 5.55a










Table 2-3. Leaf-level photosynthetic parameters. Light saturated rate of photosynthesis
(Amax, tmol C02 m-2 s-1), apparent quantum yield (Aqe, ([tmol C02 m-2 s-
1)/(tmol m-2 s-1)), and light compensation point (LCP, [tmol m-2 s-1) shown
by the six species grown under high light (HL 60% full sunlight), medium
light (ML 30% full sunlight), and low light (LL 10% full sunlight).
Species codes as given in Table 2-1. Small letters show significant
differences at P < 0.05 among treatments for each species, after ANOVA and
Tukey's multiple comparison test.

Species
GI Eg Fb Ht Fs Ce
Amax
HL 8.44b 9.36a 3.76a 6.45ab 6.10b 4.79b
ML 9.36a 5.42b 2.76b 6.57a 7.66a 5.72a
LL 8.96ab 4.98b 2.080 3.34b 6.42b 4.34b

Aqe
HL 0.0056a 0.0053a 0.0109a 0.0049a 0.0080a 0.0082a
ML 0.0047a 0.0110a 0.0092ab 0.0071a 0.0046a 0.0070a
LL 0.0058a 0.0128a 0.0444b 0.0123a 0.0072a 0.0060a

LCP
HL 17.80a 16.42a 18.42a 23.60a 9.96ab 15.27a
ML 9.60b 8.30b 8.75b 12.30b 10.05a 9.50b
LL 5.15b 3.95b 5.15b 8.70b 4.80b 7.10b







34



14

12 D 60%
-r I -----
D 30%
100%
(o











.S GI Eg Fb Ht Fs Ce
S8




-4-






n -2


-4-

-6



Figure 2-1. Relative growth rate (mean (SE)) of seedlings of six Australian subtropical
rainforest trees, grown at 60%, 30%, and 10% of full sunlight. Species codes
as given in Table 2-1.












S60 %

D 30%
S10%


D 60%
D 30%
10%


E


2 15
C-

10

5
5


GI Eg Fb


Ht Fs


Figure 2-2. A) Diameter growth in (mm). B) Height growth in (cm) (mean (SE)) of
seedlings of six Australian subtropical rainforest trees grown at 60%, 30%,
and 10% full sunlight. Species codes as given in Table 2-1.














12



10

0


'4

2
0
Li 00%



12
12 -












8 -

2 -
3 %


-2















P FD m
-2
BII 10 20 C



















Figure 2-3. Light response curve of photosynthesis as a function of PPFD for A)
Elaeocarpus grandis, B) Flindersia schottiana and C) Gmelina leichhardtii
grown under three light treatments. Data points represent means +/- standard
errors (N=10). Light curves were fitted by non-linear regression using the
Mitscherlich equation.
---(----------- i----i ----i
E2 1--------------------


6* ----






















Mitscherlich equation.














12

10

E
8 -

6






0
'" 4 -








12










M 4




O A 110 %



S10 %







-2







PPFD ml m s





Figure 2-4. Light response curve of photosynthesis as a function of PPFD for A)



+/- standard errors (N=10). Light curves were fitted by non-linear regression
using the Mitscherlich equation.














CHAPTER 3
POTENTIAL FOR SUBTROPICAL RAINFOREST RESTORATION ON
ABANDONED AGRICULTURAL LANDS IN NEW SOUTH WALES, AUSTRALIA

Introduction

Development of restoration focused activities is the antithetical response to

progressive degradation and loss of forested areas within New South Wales. During the

short duration of European settlement, rainforest lands within NSW decreased by more

than 750,000 ha (Baur 1991). In an area of New South Wales known as the "Big Scrub,"

rainforests diminished from a pre-settlement figure of 75,000 ha to less than 300 ha today

(Floyd 1990).

The prospects for conservation beyond remnant rainforest relics remained uncertain

until the late 1970s and early 1980s, whereupon a vocal majority began to question

traditional forestry operations (Adam 1992). Following fervent public opposition over

rainforest logging, the New South Wales government enacted legislation in the late 1980s

placing state-owned subtropical rainforests on the World Heritage register, and

subsequently halting timber extraction on state-owned subtropical rainforests (Adam

1992; Erskine et al. 2005). The loss of a timber resource on state-owned lands created a

novel opportunity for growing rainforest trees in plantations to supply high-value cabinet

timbers, along with the chance to restore some diversity to abandoned and degraded

agricultural lands (Glencross and Nichols 2005; Erskine et al. 2005).

The biggest challenge facing rainforest restoration today is limited information on

growth and performance of rainforest species. A flourishing opportunity exists, for









restoration and rehabilitation of degraded rainforest lands, contingent upon an

understanding of the ecology of rainforest species and an elucidation of silvicultural

requirements for long-term maintenance and sustainability of subtropical rainforest. The

burgeoning potential results from a proliferation of formerly forested areas which were

once used for agriculture and dairying, and are now abandoned and exist bereft of any

rainforest element (Kooyman 1996; Erskine et al. 2005). Rainforest restoration becomes

an option when degraded and damaged forest landscapes display reduced productivity,

biodiversity, and limited return of goods and services (Lamb and Gilmour 2003). Much

of the formerly forested land within New South Wales embodies a landscape of limited

productivity and major reduction in biodiversity. These sites present an opportunity to

implement restoration activities aimed at remediation and rehabilitation of the degraded

and damaged condition under which they now exist (Kooyman 1996; Big Scrub

Rainforest Landcare Group 1998).

To moderate complexity associated with restoration activities, numerous studies

have detailed photosynthetic and growth responses to light environments (Walters et al.

1993; Walters and Reich 1996; Valladares et al. 2002). Measuring photosynthetic and

growth responses can reveal valuable information concerning tolerance and growth of

species to a range of habitat conditions (Aleric and Kirkman 2005). Rainforest trees are

generally classified into two functional groups, based on their germination and

establishment requirements (Swaine and Whitmore 1988). Shad-tolerant species can

grow, germinate, and survive in a low light environment, whereas light-demanding

species require a high light environment to establish (Poorter 1999). Discerning between

the two functional groups allows an interpretation of appropriate silvicultural regimes for









growth and performance of rainforest trees, thus enhancing the potential utilization of

subtropical rainforest tree species in forest management or rainforest restoration projects

(Chazdon et al. 1996).

To aid the development of suitable silvicultural regimes and rainforest restoration

projects within New South Wales, the study assessed the photosynthetic response of 7

subtropical rainforest tree species growing in an under-utilized agricultural field in

northern New South Wales, Australia.

Materials and Methods

Study Site

The field study was conducted between March 2005 and April 2005 at an under-

utilized agricultural field, which beginning in May 2002 was converted towards a

subtropical rainforest restoration site. The field site is located approximately 9 km

southwest of Mullumbimby, NSW and approximately 12 km northeast of Byron Bay,

NSW. The field site is situated in the subtropical rainforest region of northeastern NSW,

at an altitude of 35 meters. Rainfall in the study region averages over 1700 mm per year.

The average annual temperature in the study region is (23.70C) with average annual

temperature in March of (26.50C) and average in April of (24.5C) (Bureau of

Meteorology, Australia). Soils of the region consist of deep, well-drained krasnozems

(FAO classification-(Luvisols), USDA classification-(Rhodoxeralfs), derived mainly

from tertiary basalt flows (Isbell 1998).

Species

Seven rainforest species were selected, based on the regeneration stages they are

known to be associated with in a regenerating forest, including those that form part of the

mature forest (Floyd 1990; Kooyman 1996). Four main groups were recognized: pioneer,









early secondary, late secondary and mature phase species (Table 3-1). Pioneer and early

secondary species are well suited to regenerate on disturbed and open sites, but are

characterized by a short life-span (Whitmore 1983; Swaine et al. 1987). Conversely, late

secondary and mature phase species are well suited to regenerate under shade, and may

live considerably longer (Whitmore 1983; Swaine et al. 1987). All species are

considered particularly viable for restoration and mixed species plantation work within

New South Wales (Kooyman, 1996; Big Scrub Rainforest Landcare Group 1998).

Photosynthetic Gas Exchange

Light response curves were measured on a leaf area basis with a LICOR-6400

portable photosynthesis system (Li-Cor, Inc., Lincoln, Nebraska USA) using the "LIGHT

CURVE" automatic program with an artificial red/blue LED light source. Measurements

were made at light levels of 2000, 1500, 1000, 500, 200, 100, 50, 20, and 0 mrnol m-2 s-

. The leaf chamber environment was maintained at the following: C02, 370 [tmol m-2.

s and temperature, 26 C. Photosynthetic measurements were made on 5 randomly

selected 3-year old saplings of each species. Photosynthetic measurements were taken

from 0700 to 1300 hours under clear to partly cloudy skies (March 2005 to April 2005)

on the most recent fully expanded leaf. Prior to the start of each light response curve

each selected leaf was placed in the leaf chamber at 1500 [tmol m-2 s-1 for 5 minutes.

The order of treatments and the replicates of 3-year-old saplings used were randomly

selected each day.

Nutrient Content

A representative sample of leaves was gathered for all seven species, and analyzed

by the Environmental Analysis Laboratory located on the campus of Southern Cross









University, Lismore, New South Wales, Australia. Samples were combusted at 5500C and

digested with nitric acid to discern total nutrients. Concentration of nitrogen was

determined using a LECO CNS2000 Analyzer. Nutrient analysis facilitated an evaluation

of the relative proportion of specific nutrients (nitrogen, phosphorous, potassium, and

sulphur) of selected leaves from the 75% full sunlight treatment (Table A-2).

Statistical Analysis

Light curves were fitted by nonlinear regression using the Mitscherlich model

equation (Sigma Plot 9.0, SSPS Inc., Chicago, Illinois USA) (Potvin et al. 1990; Peek et

al. 2002; Aleric and Kirkman 2005):

A = Amax [1 e-Ae(PPF-LCP)]

where Amax represents the asymptote of photosynthesis, Aqe corresponds to the initial

slope of the curve, PPF represents the incident photosynthetic photon flux, LCP denotes

the x intercept, where net photosynthesis is equal to 0, and A represents net

photosynthesis. This model was used to identify the following parameters: Amax, the light

saturated rate of photosynthesis, Aqe, the apparent quantum yield, and LCP, light

compensation point.

Analysis of variance (ANOVA) was used to compare the effect of light

environment on photosynthetic characteristics and growth parameters (SAS 9.0, SAS

Institute Inc., Cary, North Carolina USA).

Results

An analysis of species height at three years showed a significant difference between

species (F6,105=28.21, P<0.0001) with a range (Figure 3-1) from 2.73 m to 5.26 m.

Diameter after 3 years also displayed a significant difference between species

(F6,105=32.15, P<0.0001) with a range (Figure 3-1) from 0.0024 m to 0.0070 m. Stem









volume index (SVI) (Figure 3-2) at three years displayed wide variability between

species (F6,105=24.67, P<0.0001) with Lophostemom. confertus providing peak SVI,

followed by Elaeocarpus grandis, Flindersia brayleyana, and Gmelina leichhardtii.

Species displaying reduced SVI values included Flindersia schottiana, Heritiera

trifoliolatum, and Castanospermum australe.

Light saturated rates of photosynthesis (Amax) displayed a significant difference

between species (F6,28=62.21, P<0.0001), with a range from 5.68 to 17.16 [imol CO2 m2 s1

(Table 3-2)(Figures 3-3, 3-4 and 3-5). Patterns of photosynthetic response closely

approximated results gathered from a shadehouse experiment where a subset of the

sample species were studied (Kelly et al. 2006), with early secondary species displaying

greater light saturated rates of photosynthesis (Amax) than late secondary and mature stage

species. L. confertus provided an exception to this pattern, exhibiting a higher Amax than

all study species besides E. grandis, an early secondary species. In addition to between

species variability in light saturated rates of photosynthesis, the apparent quantum yield

(Aqe) displayed a significant difference between species (F6,28=27.52, P < 0.0001), along

with the witnessing of a significant difference between species in light compensation

point (LCP) (F6,28=7.59, P < 0.0001).

Discussion

Rainforest species experience dramatic variability throughout their lifetimes, from

daily changes in sunfleck occurrence to more drastic changes in light availability

resulting from large-scale canopy disturbance (Chazdon et al. 1996). Rainforest species

respond to these environmental perturbations through acclimation, which provides for

environmentally-induced changes in photosynthetic utilization of light, based upon the

light environment under which leaves develop (Chazdon et al. 1996). Species which









have developed under high light generally have higher light saturated rates of

photosynthesis (Amax) and higher light compensation points (LCP) (Lambers et al. 1998).

This pattern remained consistent in the field study, with species common to the

shadehouse and field study displaying higher light saturated rates of photosynthesis and

higher light compensation points under open grown conditions. Maximum rates of

photosynthesis for species in the field study ranged from 5.68 to 17.16 imol CO2 m-2 s-1

closely approximating the 10-15 imol CO2 m-2 s-1 reported for sun leaves (Loach 1967;

Larcher 1995).

Many previous studies have dictated enhanced performance of sun grown

individuals, although a demarcation exists between early and late successional species

(Strauss-Debendetti and Bazzaz 1991; Poorter and Oberbauer 1993). Early successional

species generally exhibit greater plasticity in photosynthetic capacity compared to later

succesional species (Chazdon et al. 1996). Predictable patterns followed throughout the

field study, with early successional species displaying greater Amax compared with late

successional and mature stage species. An exception occurred with L. confertus, a

mature stage species, which displayed comparable Amax to early and late successional

species. Similar findings occurred with the late successional Australian species Acmena

ingens (Turnbull 1991), suggesting that the extent of photosynthetic plasticity exhibited

by a species is not always a good predictor of its acclimation potential (Chazdon et al.

1996).

Species grown in field conditions experience greater environmental perturbation,

through decreased soil moisture, increased herbivore damage, and increased competition

for water and nutrients from surrounding vegetation. In addition, they experience greater









complexity in the light environment, in terms of spectral quality and sunflecks (Dalling et

al. 1999; Bloor 2003). Thus, identifying species response to natural environmental

perturbation can provide further evidence towards determining the potential of

subtropical rainforest species in rainforest restoration and mixed species plantation

efforts.

Based on the results of the field study, most species segregate into two distinct

groups of light-demanding and shade-tolerant. Light-demanding species include E.

grandis, F. schottiana, and include the interlopers: L. confertus, a mature stage species,

and G. leichhardtii, a late successional species. The shade-tolerant group includes C.

australe, F. brayleyana, and H. trifoliolatum. Most species represent a continuum of

responses to light, thus suggesting a cataloguing as generalists rather than specialists

(Osunkoya et al. 1994). In the tropical rainforest it has been suggested that most if not all

species may be catalogued as generalists rather than specialists (Chazdon et al. 1996).

Many species exhibit ample plasticity when responding to light availability at a given

site, thus, allowing greater exploitation of more variable environments than species with

narrower acclimation responses (Atwell et al. 1999).

The species in the field study displayed great potential for acclimation to high light

environments, thus indicating that a wide range of planting and silvicultural mechanisms

might be effective in managing these species. For example, the potential of these species

under close to full sunlight conditions (75% full sunlight) allows for planting in cleared

or under utilized agricultural fields, in large gaps of remnant rainforest, and near edges of

existing rainforest remnants. Photosynthetic and growth potential of study species under

close to full sunlight conditions provides for use in rainforest restoration across numerous









sites devoid of rainforest vegetation. The responses of E. grandis, G. leichhardtii, and L.

confertus under close to full sunlight conditions (75% full sunlight) provides strong

support on their potential for rapid growth and related rapid canopy closure, whereas the

remaining species appear better suited for plantings under an intact canopy or in

situations where the light environment remains at levels less than 75% full sunlight. To

understand more fully the potential of these seven rainforest species under close to full

sunlight conditions, further research should be conducted evaluating influencing factors

to photosynthetic performance such as constraints by ontogeny (Rice et al. 1993; Gedroc

et al. 1996), by resource availability (Bloom et al. 1985), and by loss to pests and

pathogens. Determining the impact of these factors will greatly facilitate a deeper

understanding of species ecology, natural history, distribution, and growth and

performance potential.










Table 3-1. Life history data for the study species.
Max Max
height DBH
Species Symbol (m) (cm) Successional stage
Castanospermum australe Ca 35 100 Mature
Elaeocarpus grandis Eg 35 200 Early secondary
Flindersia brayleyana Fb 40 250 Late secondary
Flindersia schottiana Fs 45 100 Early secondary
Gmelina leichhardtii GI 40 150 Late secondary
Heritiera trifoliolatum Ht 45 200 Mature
Lophostemom confertus Lc 40 200 Mature
*Adapted from Floyd 1990 and Kooyman 1996.


Table 3-2. Leaf-level photosynthetic parameters: Light saturated rate of photosynthesis
(Amax, pmol CO2 m-2 s-1), apparent quantum yield (Aqe, (pmol CO2 m-2 s
)/(pmol m-2 s-1)), and light compensation point (LCP, pmol m-2 s-1) shown by
the seven species grown under 75% full sunlight. Species codes as given in
Table 3-1.

Species
Ca Eg Fb Fs GI Ht Lc

Amax 9.85 17.16 8.50 13.41 12.77 5.68 16.91

Aqe 0.0025 0.0025 0.0029 0.0033 0.0025 0.0056 0.0024

LCP 25.90 20.50 19.16 20.50 18.70 28.50 29.80










































Lc Fb Eg GI Fs Ht Ca


Fb Ea


GI Fs


Ht Ca


Figure 3-1. A) Diameter growth (m) and B) height growth (m) (mean (+/- SE)) of
seedlings of seven Australian subtropical rainforest trees at 3 years, grown
under 75% full sunlight. Species codes as given in Table 3-1.


S 0.04
E

0.03


0.02


0.01


Ao
--- '


600




500




400

E

C 300




200




1 00




000
-












0.0350



0.0300 -



0.0250 -
-

0


a



'5

0.0100



0.0050


0.0000 ----


Fb Eg GI Fs Ht Ca


Figure 3-2. Stem Volume Index (SVI) (m3) (mean (+/- SE)) of seedlings of seven
Australian subtropical rainforest trees at 3 years, grown under 75% full
sunlight. Species codes as given in Table 3-1.







50




20-









rr


115 -T






E 15 T
8







MM
A ".. 75%











E













20 01 10 20







0 I0 10- 1500 2000
PPF (p m al m~ s")


Figure 3-3. Light response curve of photosynthesis as a function of PPFD for A)
Elaeocarpus grandis B) Flindersia schottiana and C) Gmelina leichhardtii
grown under 75% full sunlight. Data points represent means +/- standard
errors (N=5). Light curves were fitted by non-linear regression using the
Mitscherlich equation.







51





20



15-



0 10

E





S5-

F A 75%

0 500 1000 1500 200




20



P 15


0

-3
o 10







'- AN 75%


0 500 1000 1500 2000

PPFD (pmol m s)



Figure 3-4. Light response curve of photosynthesis as a function of PPFD for A)
Flindersia brayleyana and B) Lophostemom confertus grown under 75% full
sunlight. Data points represent means +/- standard errors (N=5). Light curves
were fitted by non-linear regression using the Mitscherlich equation.







52





20



15


0
o 10








a FA]


o 500 1 OO 1500 2000
0

--









O







r
.- 75%
15
















0 500 1000 1500 2000

PPFD (pmol mrn" s-'}



Figure 3-5. Light response curve of photosynthesis as a function of PPFD for A)
Castanospermum australe and B) Heritiera trifoliolatum grown under 75%
full sunlight. Data points represent means +/- standard errors (N=5). Light
curves were fitted by non-linear regression using the Mitscherlich equation.
Fiue35 ih epne uv fpooytei s ucino PDfrA














CHAPTER 4
SUMMARY AND CONCLUSIONS

Shadehouse and field studies were conducted, to elucidate ecophysiological

variability of subtropical rainforest trees to altering light environments, in order to

augment current knowledge of species potential for rainforest restoration projects and

mixed species plantations. Presumed responses of rainforest species to sun or shade

followed those developed by Swaine and Whitmore (1988), in which species are divided

into a light-demanding and shade-tolerant dichotomy. The current study also included an

additional caveat, that species response to sun or shade depends upon acclimation

potential, which is equally affected by constraints during ontogeny, by resource

availability, and by loss to herbivores (Bloor and Grubb 2004). To evaluate and ascertain

acclimation potential, experiments were conducted under controlled conditions in a

shadehouse and under natural conditions at a field site.

Many past studies have utilized information on growth and photosynthetic potential

to ascribe ideal growing and silvicultural situations in which to enhance performance of

species (Boardman 1977; Walters et al. 1993; Walters and Reich 1996). Rainforest

species are typically depicted as belonging to one of two broad guild associations

(Swaine and Whitmore 1988). Light-demanding or gap requiring species germinate in

treefall light gaps, have high mortality rates, are light-demanding and grow rapidly, while

shade-tolerant species germinate, grow, and have high survivorship in deep shade (Condit

et al. 1995; Chazdon et al. 1996; Strauss-Debenedetti and Bazzaz 1996; Press et al. 1996;

Whitmore 1996). Two questions were asked during the study to further elaborate on









species successional status and acclimation potential: 1) What photosynthetic adjustments

are made by study species in response to variation in the light environment? 2) Do

morphology, growth, and biomass differ for seedlings growing in different light

environments?

In this study, hypotheses to aforementioned questions focused upon successional

attributes and acclimation potential of study species. In general, these hypotheses

predicted enhanced photosynthetic rates of early successional species in high light and

greater potential for physiological acclimation of early successional species across a light

gradient. Hypotheses on growth parameters, predicted heightened relative growth rates

for early successional species across a light gradient, with ample potential for

morphological plasticity across a light gradient. Conversely, hypotheses for shade-

tolerant species depicted reduced photosynthetic rates in high light and limited potential

for physiological acclimation across a light gradient. In addition, shade-tolerant species

were predicted to display limited variation in growth parameters and limited ability for

morphological plasticity across a light gradient.

Based on results acquired from the shadehouse study, physiological responses fall

between an opaque demarcation of early and late successional species. Elaeocarpus

grandis provided a clear representation of an early successional species, with marked

increase in Amax in high light and an ability to down regulate photosynthetic machinery in

low light conditions. The remaining species (Flindersia brayleyana, Flindersia

schottiana, Gmelina leichhardtii, and Heritiera trifoliolatum) were better represented as

falling along a shade-tolerant continuum, with limited ability to adjust physiologically to

an increase or decrease in light, maintaining similar Amax across all light environments.









Morphological change across a light gradient, in the shadehouse experiment,

provided greater discernment of common successional patterns. In high light, all species

displayed a peak in RGR, except for the facultative shade-tolerant species Cryptocarya

erythroxylon which displayed a peak in 30% full sunlight. Early and late secondary

species displayed heightened RGR compared to mature stage species, which may be

accounted for by the inherent capacity for high SLA in early successional species

(Lambers and Poorter 1992; Reich et al. 1998). Patterns in SLA closely approximated

the perceived early and late successional dichotomy. In the shadehouse study, early and

late secondary species (E. grandis, F. brayleyana, F. schottiana, and G. leichhardtii)

displayed an ability to modulate SLA when moving from high to low light, whereas

mature stage species (C. erythroxylon and H. trifoliolatum) displayed limited potential to

modulate SLA in response to variable light.

Results from the field study closely corroborated observations from the shadehouse

study. Species in the shadehouse which displayed maximum Amax in the 60% full

sunlight treatment (E. grandis and F. brayleyana) continued to display heightened Amax

in the 75% full sunlight field study. Remaining species occurring in both studies (F.

schottiana, G. leichhardtti, and H. trifoliolatum) displayed enhanced Amax under high

light conditions present in the field study; in contrast to a peak in Amax under moderate

light (30% full sunlight) in the shadehouse study. This condition strongly suggests the

influence of ontogeny on acclimation potential of study species (Rice et al. 1993; Gedroc

et al. 1996), as species developing under high light conditions generally display increased

light saturated rates of photosynthesis (Amax) and light compensation points (LCP)

(Lambers et al. 1998). Species evaluated solely in the field study (Castanospermum









australe and Lophostemom confertus) also displayed heightened Amax, closely

approximating the typical range for sun leaves of 10-15 [tmol CO2 m-2 s-1 (Loach 1967;

Larcher 1995).

This study provides important insight into potential of subtropical rainforest species

to a range of light environments. Results show that most species belong to a shade-

tolerant constituency, with an ability to grow and persist across a wide range of light

environments. Growth and photosynthetic performance of most species reached a

maximum in 30% to 60% full sunlight found in shadehouse conditions. Species under

natural conditions displayed an ability to acclimate to heightened light conditions,

reaching their highest Amax in 75% full sunlight, and thus providing credence to the

influence of ontogeny on species performance.

In conclusion, study species offer a wide range of potential planting scenarios and

silvicultural options, with ample potential to achieve rapid canopy closure and restoration

goals. This study indicates promise for inclusion of study species in rainforest restoration

activities and in the development of mixed species plantations. Ascertaining a complete

understanding of species performance will require further research into characteristics

leading to species growth performance and those characteristics which provide for

maintenance, persistence, and storage (Kitajima 1994; Kobe 1997). In light of this,

further research should be conducted for subtropical rainforest species to elucidate the

response of species to pests, pathogens, and resource availability.















APPENDIX
NUTRIENT CONCENTRATION

Table A-1. Total nutrient concentration in leaves of six subtropical rainforest species


grown under HL (60%), ML (30/
codes as given in Table 2-1.


o) and LL (10%) full sunlight. Species


Species
Units GI Eg Fb Ht Fs Ce
Nitrogen %
HL 1.24 1.12 0.87 2.23 1.43 1.43
ML 1.58 1.25 1.04 2.44 1.62 1.61
LL 2.00 1.84 0.87 2.07 1.71 1.83

Phosphorus %
HL 0.05 0.09 0.05 0.11 0.19 0.09
ML 0.07 0.10 0.06 0.10 0.16 0.12
LL 0.08 0.10 0.06 0.08 0.16 0.11

Potassium %
HL 0.44 0.60 0.25 0.92 0.68 1.03
ML 0.82 1.04 0.30 0.98 0.54 1.20
LL 0.89 0.99 0.31 0.89 0.46 1.51

Sulphur %
HL 0.10 0.13 0.08 0.15 0.11 0.12
ML 0.10 0.13 0.12 0.17 0.14 0.16
LL 0.13 0.17 0.12 0.15 0.15 0.14







58




Table A-2. Total nutrient concentration in leaves of seven subtropical rainforest species
grown under 75% full sunlight. Species codes as given in Table 3-1.

Species
Nutrient Units Ca Eg Fb Fs GI Ht Lc
Nitrogen % 2.32 1.98 2.17 2.31 1.47 1.63 1.45
Phosphorus % 0.14 0.16 0.11 0.15 0.10 0.10 0.11
Potassium % 0.57 0.98 0.81 0.83 0.90 1.42 0.64
Sulphur % 0.15 0.15 14.86 0.15 0.09 0.12 0.11















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BIOGRAPHICAL SKETCH

Jeffrey W. Kelly was born in Orlando, Florida, during the decadent '70s. He

moved to Salt Lake City at the age of one, whereupon he spent the first third of his life

planning an escape from the confines of the renowned conservative mecca of SLC. To

hasten an escape, he diligently worked to receive a Bachelor of Science degree in

Forestry from Utah State University. Following his studies at Utah State University, Jeff

contacted Dr. Shibu Jose at the University of Florida to inquire about potential research

opportunities. Dr. Jose spoke of an opportunity to research rainforest restoration in

Australia, which sparked quite the interest and led to the beginning of a wonderful

experience researching Australian rainforests.

Jeff is currently working with the Pacific Northwest Fire Sciences Laboratory of

the U.S. Forest Service in Seattle, Washington.