Citation
Growth Rate of Tectona Grandis and Cedrela Odorata in Monoculture and Mixed Species Systems in Belize, Central America

Material Information

Title:
Growth Rate of Tectona Grandis and Cedrela Odorata in Monoculture and Mixed Species Systems in Belize, Central America
Creator:
Garcia-Saqui, Juanita I
Place of Publication:
[Gainesville, Fla.]
Florida
Publisher:
University of Florida
Publication Date:
Language:
english
Physical Description:
1 online resource (67 p.)

Thesis/Dissertation Information

Degree:
Master's ( M.S.)
Degree Grantor:
University of Florida
Degree Disciplines:
Interdisciplinary Ecology
Committee Chair:
Jose, Shibu
Committee Members:
Bannister, Michael E.
Stepp, John R.
Graduation Date:
8/11/2007

Subjects

Subjects / Keywords:
Agriculture ( jstor )
Forests ( jstor )
Monoculture ( jstor )
Nutrients ( jstor )
Pests ( jstor )
Plantations ( jstor )
Soil science ( jstor )
Species ( jstor )
Transgenetic organisms ( jstor )
Trees ( jstor )
Interdisciplinary Ecology -- Dissertations, Academic -- UF
agroforestry, belize, cedrela, grandis, mixed, monoculture, odorata, species, tectona
Genre:
bibliography ( marcgt )
theses ( marcgt )
government publication (state, provincial, terriorial, dependent) ( marcgt )
born-digital ( sobekcm )
Electronic Thesis or Dissertation
Interdisciplinary Ecology thesis, M.S.

Notes

Abstract:
This study seeks to understand the importance of mixed species agroforestry systems in Belize. It investigated the growth patterns of two hardwood tree species: Cedrela odorata L. (Cedar) and Tectona grandis L. (Teak) grown in mixed-species and monoculture plots to determine which type of system provides the best growth pattern. The hypothesis was that hardwood tree species grown in managed mixed-species system would grow better because of complimentary interactions between species. The results showed that the hardwood trees grew faster in mixed-species systems than in the monoculture treatment. However, C. odorata was found to be more prone to attacks by Hypsypla grandella Zellar (shoot borer) in the mixed species system than in the monoculture plots, which reduced their height growth when compared to the monoculture plot. Despite the H. grandella attacks of C. odorata, the mixed species system had higher land equivalent ratio (LER) compared to the monoculture treatment, indicating that mixing species was advantageous over growing the species in monoculture. An investigation to compare soils in both systems revealed that the mixed system improved soil fertility (higher cation exchange capacity) compared to the monoculture treatment. Future research should examine soil and canopy nutrient dynamics in detail so that the underlying mechanisms for the observed yield advantage in mixed species system can be unveiled. ( en )
General Note:
In the series University of Florida Digital Collections.
General Note:
Includes vita.
Bibliography:
Includes bibliographical references.
Source of Description:
Description based on online resource; title from PDF title page.
Source of Description:
This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Thesis:
Thesis (M.S.)--University of Florida, 2007.
Local:
Adviser: Jose, Shibu.
Statement of Responsibility:
by Juanita I Garcia-Saqui.

Record Information

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UFRGP
Rights Management:
Copyright Garcia-Saqui, Juanita I. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
Resource Identifier:
660373844 ( OCLC )
Classification:
LD1780 2007 ( lcc )

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Full Text





Ecological basis for mixed species systems

The ecological foundation for mixed species agroforestry systems lies in the

structural and functional diversity the plantings create at both the site and landscape

levels. Mixed species plantings can help add structural and functional diversity to

landscapes and, if strategically located, they can help restore many ecological functions

(Ruark et al., 2003). Mixed species systems are common worldwide. Most agricultural

production especially in developing countries is done using this type of production

(Aron, 1972; Alas, 1974; Nair, 1990). Since it is so common it has attracted a lot of

attention, especially because there are so many systems which are referred to as mixed

species or intercropped systems. Vandermeer (1989) lists a total of 55 combinations, but

Nair (1990) reported more than 150 systems. According to Lamberts (1980) there are

several reasons for cultivating in mixed species systems, and these include

increased productivity or yield advantages;
better use of available resources (land, water, nutrients, labour, time);
reduction in damage caused by pests (diseases, insects, weeds);
food and cash-flow (economics, human nutrition, greater stability etc.).

This aspect of mixed species systems look at the organism and environment

interactions in which the organism and the environment affect one another. Hence a plant

may influence its neighbour by changing its environment resulting in an effect and

response reaction by the individuals involved. The changes need not be negative, but

requires a response from the other plants such that a plant may either deplete a resource

or may enhance it making it available for its neighbour. However, there are changes that

may result in negative effects such as nutrient extraction that leads to depletion of a

resource or production of shade which may not be good for another individual. A positive






57


ecology with a concentration in forest resources and conservation. Juanita has been

married to Mr. Pio Saqui for eight years.









Montagnini, F., Sancho, F., Gonzalez, E., Moulaert, A., 1993. Mixed-tree plantations
with indigenous trees in the Atlantic lowlands of Costa Rica. In: Parrotta, J.A.,
Kanashiro, M. (Eds.), Proc. Int. Symp. on Management and Rehabilitation of
Degraded Lands and Secondary Forests in Amazonia. Santarem, Para, Brazil, 18-
22 April, 1993, IITF, USDA Forest Service, Puerto Rico, pp. 161-169.

Morales, H. and I. Perfecto., 2000. Traditional knowledge and pest control in the
Guatemalan highlands. Agriculture andHuman Values 17, 49-63.

Moran E.F., Brondizio E.S., Mausel P. and Wu, Y., 1994a. Deforestation in Amazonia:
Land Use Change from Ground and Space Level Perspective. Bioscience 44, 329-
339.

Nair, P. K. R., 2001. Agroforestry. pp. 375-393. In: Our Fragile World: Challenges and
Opportunities for Sustainable Development, Forerunner to The Encyclopedia of
Life Support Systems, Chapter 1.25, Vol. I. UNESCO, Paris, France, & EOLSS,
UK.

Nair, P. K. R., Buresh, R.J., Mugendi, D.N. and Latt C.R., 1999. Nutrient cycling in
tropical agroforestry systems: Myths and science. pp.1-31. In: L. E. Buck, J.P.
Lassoie, and E.C. Fernandes. (eds), Agroforestry in Sustainable Agricultural
System. CRC Press, Boca Raton, FL.

Nair, P.K.R., 1990. The Prospects for Agroforestry in the Tropics. Washington DC:
World Bank Technical Paper No. 131.

Netting, R. N., 1993. Small-holders, Householders: Farm Families and the Ecology of
Intensive, Sustainable Agriculture. Stanford, Stanford University Press.

Netting, R. N., 1965. Household Organization and Intensive Agriculture: The Kofyar
Case. Africa 35, 422-429.

Netting, R. N., 1963. Kofyar Agriculture: A Study in the Cultural Ecology of a West
African People. Ph. D. University of Chicago.

Nye, P.H. and Greenland D.J., 1960. The Soil Under Shifting Cultivation. Harpenden,
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51.

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Change. Bioscience 44, 300-304.

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species plantations of Casuarina equisetifolia, Eucalyptus robusta, and Leucaena
leucocephala in Puerto Rico. For. Ecol. Manage. 124, 45-77.

Parrotta, J.A., 1995. Influence of overstory composition on understory colonization by
native species in plantations on a degraded tropical site. J. Veg. Sci. 6, 627-636.









Mean rainfall in this area during the study period ranged from 75 mm to 286 mm

per month between May through August with the wettest month being in August and the

driest month in July 2005. Rainfall pattern differed in 2006 during which there was more

rainfall during the months of June and July declining in August (Figure 2-2).

This research was carried out in conjunction with an ongoing agroforestry research

project funded by the Organization of American States. Hardwood trees species grown in

the western parts of Belize in the Cayo District provide an excellent case study for the

potential of hardwood tree species systems to address the needs of limited timber

resources in Mesoamerica and the Caribbean.

Experimental Design and Measurements

The experiment was set up as a completely randomized design with five

replications. Each plot was 471.5 m2 and contained 40 trees. The two treatments were

monoculture (C. odorata or T. grandis alone; i.e. 40 trees of the same species per plot)

and mixed species plantation (C. odorata and T. grandis mixed together in the same plot

for a total of 40 trees per plot; i.e. 20 trees of each species). The mixed species plot also

had ground cover of Arachispintoi, Swietenia macrophylla and the leguminous trees,

Lonchocarpus castilloi, and Sweetia panamensis. However only C. odorata and T.

grandis were used in this research. The crops that have been traditionally intercropped in

the mixed species plots have been hot peppers (Capsicum chinense Jacq) and papayas

(Caricapapaya). The hardwood trees studied were pruned after the first three years.

Each hardwood tree and leguminous trees were systematically planted at a distance of 5

m from each other (the papaya and hot peppers were intercropped in the space between

the trees) The trial did not receive any irrigation, fertilizers and pest control.






46


important for plant production and also for the survival of organisms which are the

recyclers of nutrients. In summary, mixed species systems have many advantages for

farmers and can be practiced as an alternative land use strategy.















BIOGRAPHICAL SKETCH

Juanita Garcia-Saqui was born in Stann Creek, Belize C.A. She is the fourth

daughter and fifth child born to Reverend Juana Garcia-Gutierrez and Jorge Garcia.

Juanita Garcia began her education at the Light of the Valley Baptist Primary School.

Because of financial constraints, Juanita had to stay out of school for two years before

entering high school. Therefore after two years following the Baptist Primary School,

she was enrolled at the Ecumenical High School. In 1992, she graduated from

Ecumenical High School, and because of financial constraints, she was forced to enter the

work force. She worked for six years, after which she returned to the University of

Belize in 1999 where she obtained an associate's degree in natural resources management

in 2001. After her associates degree, Juanita pursued and obtained a bachelor's degree in

biology in 2003.

While pursuing her bachelor's degree, Juanita also worked as an assistant

laboratory technician for the Micro propagation laboratory at the University of Belize,

where she assisted in the tissue culturing of native orchids of Belize. After obtaining

her bachelor's degree Juanita took full responsibility of the micro propagation laboratory

and worked appointed by the University of Belize as a consultant for the OAS project in

Belize which is affiliated with the University of Belize.

In 2004, Juanita was accepted with funding to the University of Florida in the

School of Natural Resources and Environment, where she majored in interdisciplinary













CHAPTER 2
GROWTH RATE OF TECTONA GRANDIS AND CEDRELA ODORATA IN
MONOCULTURE VERSUS MIXED SPECIES PLANTATIONS IN BELIZE

Introduction

The forests of Belize cover slightly more than 85% of its surface area which is very

different when compared to neighboring countries in Central America that have not been

as successful as Belize in protecting their forests. According to the FAO the rate of

deforestation in Belize is relatively low (i.e., approximately 0.25% per year compared to

other countries in the region) (FAO, 1997). The vast majority of these forests, situated in

central and southern Belize, are tropical rainforests which constitute an important

reservoir of biodiversity worldwide. Furthermore, they are an important source of wood,

medicinal plants, and all kinds of natural products (Bruntland, 1989; Boot, 1997).

Although Belize has been able to preserve most of its environmental resources to a

much greater extent than other Central American and Caribbean countries, its economy

has been and will remain highly dependent on environmentally-based industries (FAO,

2001). The forests of Belize are by no means undisturbed; they are dynamic and range

from freshly burned milpas to dense tropical forests.

The main cause of forest degradation in Belize is slash-and-burn agriculture (with

no fallow period), as practiced by the Maya and the Mestizo population (Arya and Pulver,

1993). Slash and bur agriculture in Belize leads to permanent agriculture; in which

crops are rotated initially, but become permanent at a later stage. It is in this system that

the mixed species is mostly centered on, because trees are planted for several purposes

including food, fodder, timber and medicinal purposes among other uses.









Bermejo, I., Canellas, I., San Miguel A., 2004.Growth and yield models for teak
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in pure and mixed stands of Eucalyptus saligna and nitrogen-fixing Facaltaria
moluccana. Forest Ecology and Management 182, 93-102.

Binkley, D., O'Connell, A.M., Sankaran, K.V., 1997. Stand development and
productivity. In: Nambiar, E.K.S., Brown, A.G. (Eds.), Management of Soil,
Nutrients and Water in Tropical Plantation Forests. ACIAR/CSIRO/CIFOR,
ACIAR, Canberra, Australia, pp. 419-442.

Binkley, D., Dunkin, K.A., DeBell, D., Ryan, M.G., 1992. Production and nutrient
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Change Under Population Pressure. Chicago: Aldine.

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Changing Concepts of Agricultural Intensification and Peasantry in the Amazon
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Bruntland G.H., 1989. Notre avenir a tous. Editions du Fleuve. Quebec, Canada.

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Kingdom.









hard choices are financial. Monoculture systems are deemed to yield financial benefits

within short time periods. Lands that are productive are repeatedly used, leading to

degraded and almost sterile soil conditions. It is imperative that alternative forms of

agriculture are designed; those that will allow the farmers to cultivate the same amount of

land, producing a variety of products with less impact on the environment and on the soil.

History of Agroforestry

Farmers make nutrients, water and sun light available to the plants and animals

they nurture, and they do this as simply and efficiently as they can. In intensive

agriculture the task is not so much to tap naturally existing resources, but to increase their

supply to support more biotic growth, to maintain the proper conditions over longer

duration and to replenish and regulate the supply of those elements that are exhausted.

Planting several crops together in mixed stands rather than monocropping is an age-old

practice, but practiced rarely in modern intensive agriculture. In addition to multiple

products, ground cover crops used in these mixed systems provide a stratified cover

protecting the field surface from rain and direct sunlight that can contribute to soil

degradation (Netting, 1993).

It is common knowledge that population growth demands an increase of food

production and also an increase in construction material (Ruark, Schoeneberger, Nair,

2003). Boserup's "The Conditions of Agricultural Growth" (1965) is the most cited

reference on agricultural intensification. She discusses the process of raising production

at the cost of monoculture work at lower efficiency of labor. Her influential work brought

an alternative viewpoint to the relationship between population growth and food

production, one that questioned the traditional, classical-economic approach to

agriculture based on the Malthusian paradigm. Boserup's model defined population









growing C. odorata and T grandis in mixed species plots will improve soil
quality by increasing soil organic matter and nutrient content.

Characteristics of Cedrela odorata and Tectona grandis

The species used in the current study are different in their physiology and perhaps

can compliment each other in the use of resources. C. odorata has monopodial growth,

with orthotropic branches that form an open crown. It has large, pinnately compound

leaves that can be up to a meter long, with 10-20 pairs of leaflets, each about 40 cm2

(Hiremath et al., 2002). On the other hand, T grandis has an umbrella like crown with

large, thick leaves whose leaves are simple and opposite, hence it allows the infiltration

of sufficient light for photosynthesis by the understory plants. The rooting pattern of the

trees is also of interest since it determines the extent to which these trees are tapping the

soil nutrients. T. grandis root extend to a dept of -20 feet into the soil column while C.

odorata roots are mostly superficial but becomes deeply rooted if the soil is loose or

coarse.

Materials and Methods

Study Area

The study was carried out in the Cayo District (Figure 2-1) in Belize (16050' and

17045' north latitude, and 88050' and 8901' west longitude). The soil varies in texture

from sandy loam to sandy clay but invariably contains angular quartz grit. It is acidic and

has very low contents of available plant nutrients (King, Baillie, Abell, Dunsmore, Gray,

Pratt, Versey, Wright, Zisman 1992) except for calcium. The area experiences a mean

annual rainfall of 1400 mm with a mean temperature of 260C (Figure 2-2) (Hydromet

Services, 2006).









Problem Statment

Belize has a low population density of hardwood trees species such as Swietenia

macrophylla King and Cedrela odorata L, growing naturally in the forests (Levasseur

and Olivier, 2000). In spite of this situation there is an increasing demand for hardwood

lumber locally. This demand is further intensified by the rise of new industries like

tourism, which is currently the main income generating industry in Belize (World Fact

Book, 2007). Among the various forms of tourism, ecotourism seems to demand the most

natural resources including timber. Those operations build structures that are aesthetically

appealing to foreign travelers, often requiring the use of local construction material. This

form of tourism is placing an even greater demand on lumber for the construction of

resorts instead of alternative building materials (Primack et al., 1997).

In 2001 and 2002 Belize experienced a catastrophic infestation of the Southern

Pine Bark Beetle, which totally destroyed the country's largest managed forest

ecosystem, Mountain Pine Ridge Forest Reserve. This forest was 31-years-old, and

consisted of the Caribbean White Pine (Pinus caribaea) species which was selectively

harvested for timber (GOB, 1996). The plantation is now unproductive and in a

regeneration phase. The demand for hardwood remains which has forced the logging

industry to revert to harvesting of timber in natural forest stands. This option makes

forest reserves and other unprotected forests vulnerable. With forest reserves not well

monitored (because of lack of personnel) by the Forestry Department of the Government

of Belize (GOB), many designated forest reserves are being illegally harvested. C.

odorata and S. macrophylla are the two hardwood species targeted. These species are

harvested uncontrollably in various sizes, in some cases, before the trees are at the

regulated DBH size or mature enough to reproduce. Other hardwood trees species are











350

300

E 250
S250 Rainfall05
/ temperature 05
.9 200
200 ...Rainfall 06

0' / ) temperature 06
150 A /

100 -


0

may june july august
month



Figure 2-2. Graphical description of the monthly weather patterns (temperature (C) and
rainfall (mm)) of the study region in Belize during the study period May -
August 2005 and 2006. Rainfall varied throughout the study period but
temperature remained constant.









al., 1997 and Cadisch et al., 2002b). Therefore, intercropping or mixed cropping in small

plots may have the potential to increase total yield compared to those of monoculture

plots using the same resource base (Mead and Willey, 1980). This can also result in more

efficient use of farm resources, thereby increasing economic returns (Hiebsch and

McCollum, 1987). If planned with consideration for each species' response to mixed

conditions, mixed designs can be more productive than monoculture systems (Smith,

1986; Binkley et al., 1992; Cannel et al., 1996). Both T. grandis and C. odorata are tall

trees 30 to 40 m in height. The T. grandis roots extend to a dept of -20 feet into the soil

column while C. odorata roots have been reported to be superficial with a tendency to

become deeply rooted if the soil is loose or coarse.

Improving soil quality

One of the main conceptual foundations of mixed species system is that trees and

other vegetation improve the soil beneath them. Observations of interactions in natural

ecosystems and subsequent scientific studies have identified a number of facts that

support this concept. Mixed species agroforestry systems have the ability to contribute

significantly to maintaining or improving soil and water quality in a region. However the

degree to which these and other ecological functions can be provided will depend on

plant species composition and their physical structure both above- and below-ground

(Wang et al., 1991; Stanley and Montagnini, 1999; Cusack and Montagnini, 2004; Jose et

al., 2004).

Water relations are very important because water is the medium through which

many of the resources are transported. Nitrogen dissolves in water and moves through

mass flow. On the other hand potassium and phosphorous are easily adsorbed on the

surface of soil particles and when this happens these nutrients move slow in the soil






39




Table 2-2. Foliar analysis results per treatment. Chemical characteristics of the leaves
from C. odorata and T. grandis at age four in mixed and monoculture systems
in the study site in the Cayo District, Belize.
Leaf parameters Monoculture Mixed
C. odorata T. grandis C. odorata T. grandis
Nitrogen (%) 4.5 3.8 4.7 3.9
Phosphorous (%) 0.31 0.19 0.16 0.14
Potassium (%) 3.58 2.47 2.59 2.50
Magnesium (%) 0.16 0.23 0.17 0.13
Calcium (%) 1.80 1.40 1.90 1.40






55


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Figure 2-1. Map of Belize showing project/research site in the Cayo District.









Mixed species systems are commonly used in Belize in subsistence farming.

However, there is a common perception that these systems are more time consuming to

care for and demands higher investment at the initial plantation phase. Furthermore, it is

perceived that mixed species systems are not as productive as monoculture systems, and

that the trees do not trive as well as in monoculture. It would seem to farmers that the

results are not the same as those obtained in a monoculture plantation. Hence, few

hardwood trees have been intercropped in these systems.

The ecological aspect of a mixed species system is seldom taken into consideration

when establishing hardwood tree plantations. However, several studies have shown that

mixed-species plantations have a high potential for accelerating the process of natural

succession and establishing a stand of ecologically and economically desirable trees

(Montagnini, 1999; Dommergues and Rao, 2000). Other studies have also shown that

mixed-tree plantations could be an effective tool for alleviating site degradation, acting as

a catalyst for forest regeneration and rehabilitation (Lugo, 1988; Parrotta, 1995).

The idea behind a mixed species systems is to capitalize on the beneficial

interactions between the species planted while avoiding negative interactions. Results

from studies done in Belize show that more favorable credit rates, labor saving

technology, and intensive shade management have the strongest potential to increase

smallholder income (Levasseur and Olivier, 2000). If mixed species systems were

continuously implemented adding annual shade tree crops such as fruits, nuts, or spices

there is potential to significantly improve smallholder income. Furthermore, since the

systems are usually small plots (-5ha), labor is mostly carried out by family members;









1991) and 3) the enemies hypothesis in which natural enemies are more effective and

numerous in diverse systems reducing the pests through predation or parasitism.

Therefore it can be said that the first hypothesis more closely explains observed pest

attack on the study conducted in the trees funded by the OAS in Belize although the exact

mechanism of concentration on the resource is not defined. However, there are currently

several competing explanations which are probably best summarized by Finch and

Collier (2000). These authors speculate that insect pests settle on plants only when

various host plant factors such as visual stimuli, taste and smell are satisfied. This is more

likely to occur in monocultures than in mixed species systems where the chance of

encountering a 'wrong' stimulus is much increased. Therefore, the complexity of the

overall picture makes it difficult to specifically design intercrops for pest control without

practical knowledge of pest and crop biology which sometimes can be obtained through

research and traditional ecological knowledge (Hokkanen, 1991).

There is a list of pests and diseases which a mixed species system is said to control.

These include a reduction in insect attacks, nematodes, diseases, herbivore attacks,

aphids, and weed control (Risch et al., 1983; Leibman, 1986; Andow, 1991) among

others in which a specialist pest is said to be deterred from its host through the disruptive

effect of a mixed species system of plant (Trenbath, 1976).

Current Project

The objective of the study was to examine growth and soil fertility status of

monoculture and mixed species plantations of Cedrela odorata L and Tectona grandis L

in Belize. We hypothesized that mixed species plantations will have higher soil fertility

and better growth compared to monoculture plantations because of the synergistic
















LIST OF REFERENCES

Aiyer, A.K.Y.N., 1949. Mixed cropping in India. Indian J. Agri. Sci. 19:439-543. In
Vandermeer's (1989). The Ecology of Intercropping. Cambridge University Press.
Cambridge.

Alas, L.N., 1974. Breve description del sistema de production del pequeno productor en
El Salvador. Apendice F. In Conferencia sobre systems de production agricola
para el tropico. Cent. Agron. Trop. De Invest. y Ensenanza. Informe final. CATIE.
Turrialba. Costa Rica.

Altieri M.A., 1999. The ecological role of biodiversity in agroecosystems. Agriculture
Ecosystems and Environment 74, 19-31.

Altieri M.A. and Hecht, S.B., 1990. Agroecological and Small Farm Development.
Boston: CRC Press.

Andow DA., 1991. Vegetational diversity and arthropod population response. Annual
Review ofEntomology 36, 561-568.

Arnon, I., 1972. Crop production in dry regions. Leonard Hill, London.

Arya L and Pulver E.L., 1993. On-site appraisal of target areas for sustainable agriculture
production activities. Natural Resource Management Protection Project
(NARMAP), Belmopan, Belize.

Atkinnifesi, F.K., Kang, B.T., and Fajani-Eniola, H., 1996. Root soil interface in
agroforestry systems. In: Agboola, A.A., Sobulo, O., and Obatolu, C.R. (eds)
proceedings of the third African soil science society conference, Lagos, Nigeria,
pp. 201-210.

Balee W. and Gely A., 1989. Managed Forest Succession in Amazonia: The Kaapor
Case. Advances in Economic Botany. 7, 129-158.

Behrens, C.A., Baksh M.L. and Mothes M., 1994. A Regional Analysis of Bari Land Use
Intensification and its Impact on Landscape Heterogeneity. Human ecology 22,
279-316.

Belize Meteorology Service, Hydrology Department. Personal communications (2006).
http://www.hydromet.gov.bz.









growth as the independent variable that induces intensification and increases food

production. Therefore, it is based on the frequency that the land is cropped, portraying

agriculture as dynamic and related to a broader array of land use activities and landscape

changes which is also applicable to timber production. Boserup's model further relates

intensity to frequency of cultivation, proposed in five progressive categories of

intensification: 1) forest fallow (20-25 year cycle), 2) bush fallow (6-10 years), 3) short

fallow (1-2 years), 4) annual cropping (yearly), and 5) multi-cropping (sequential).

Therefore, her model takes into consideration the environment, the use and importance of

technology and socio-economic impacts allowing for the relative elasticity, manageability

and variability of human societies. This mode of production provides a more optimistic

view than that of the Malthusians about human adaptive capacity to population growth

and environmental limitations (Brondizio and Siquiera, 1997).

Conklin (1957) is also a proponent of intensification via mixed species systems.

In his studies with the Hanunoo agriculture he challenged the simplistic view of

subsistence agriculture by showing the complexity and diversity of crop association and

the efficiency of labor input and output yields in these systems. On the other hand Netting

(1963, 1965) also showed the efficiency (biological) of intercropping or intensification

techniques with his work among the Kofyar of Nigeria. Nye and Greenland (1960)

showed the relationship between soil and shifting agriculture thereby providing a

scientific basis for understanding the efficiency of shifting agriculture and its impact on

soils. From their investigation they concluded that there was minimal soil loss through

this system of cultivation. Therefore these studies support the fact that intercropping or









mixed species systems form of cultivation is a dynamic land use system with a flexible

productive capacity.

A study done by Wilken (1987) and later by Keys (2005) provided a better

understanding of traditional agriculture and resource management practices in Mexico

and Central America. Wilken was particularly intrigued by the degree of specialization

developed by small farmers to cope with environmental and sociological limitations of

areas that are considered inappropriate for agriculture. On the other hand, McGrath

(1987) reviewed the role of biomass in mixed species cultivation and suggested that the

use of length of fallow rather than vegetation-soil complex be used to measure energy

input and intensification into this system, since burning might lead to the loss of biomass

from the system. Guillet's (1987) studies in Peru added to this information by showing

that both intensification through mixed species and intercropping systems of production

and deintensification can occur simultaneously at the regional or the community level,

noting the importance of considering the coexistence of agriculture and other crops (e.g.

trees) within a broad scope of land use.

The following work led to the emergence of two interdisciplinary approaches.

One was identified as Farming System Research (Turner and Brush, 1987) and the other

as agroecology (Altieri and Hecht, 1990). Farming System Research focuses on

technology while agroecological studies target the understanding of ecological

relationships within agricultural systems. By their very nature agroecosystems are very

manipulable. Both approaches were interested in looking at agricultural changes in the

context of socioeconomical and ecological changes. However, agroecosystems studies









are broadened by a scheme that considers production and technology as well as intensity

measures with emphasis on yield and ecological stability.

Research on agricultural intensification may be summarized under two headings:

(1) intensification analysis based on small farm agriculture and resource management,

and (2) land use analysis that places agriculture within a broader spatial and temporal

landscape proposing scales of analysis at the local, regional and global levels (Netting,

1963, 1965 and 1993). Netting's (1993) evaluation of the importance and efficiency of

small farmer intensive farming is an example of the first trend. He redefines

intensification in the light of sustainability and productivity. His conclusion was that the

disruption of small farmer agriculture in favor of modem energy-intensive technology

has recurrently deintensified agriculture and has promoted more extensive land use

systems. The second trend of agricultural studies mentioned resulted from research that

integrates approaches and methods of ecological and socioeconomic and landscape

ecology. These were deemed necessary due to the need to understand agriculture and

economics from a broader, regional scale (Brondizio et al., 1994; Moran et al., 1994a)

and to understand the impact of land use strategies in regional-scale processes (Kummer

and Turner, 1994; Ojima et al., 1994; Skole et al., 1994).

The process of integration has resulted from various unifying interests such as the

increased demand for food in less developed countries the effects of deforestation on

global biogeochemical and hydrological cycles, and the loss of biological and crop

diversity (Ruark et al., 2003; FAO, 2001; Zimmerer, 1996; Watts, 1987). Therefore by

mapping processes of human disturbance onto a landscape, translating them to the spatial















O mono nixed

3

2.5

2
C-,

(-



0.5

0---


C.odorata


a


T.grandis


Figure 2-3. The growth increment per month (measured during a 3 months active
growing season in 2005) of C. odorata and T. grandis in mixed species and
monoculture plots at the study site in the Cayo District, Belize. For each
variable, differences among treatments are statistically significant when
followed by different letter.


2


1.5


1


0.5


0
1.4

1.2

1

o 0.8

0.6

0.4

0.2

0






40



Table 2-3. Chemical characteristics of the top soil to 15 cm depth for monoculture and
mixed species systems, Cayo District, Belize. S.E is shown in parenthesis.
For each variable, differences among treatments are statistically significant
when followed by different letter using Duncan's test to note statistical
difference (n=9, p<0.05).
Soil parameters Monoculture Mixed


Soil pH (%)
Organic matter (%)
C.E.C (meq/100g)
Exchangeable K (%)
Exchangeable Mg (%)
Exchangeable Ca (%)


C.odorata T grandis
6.5(.1) a 6.9(.45)a
7.0(.45) a 5.5(.55) a
31.9(3.4) a 40.9(5.3) a
0.55(.05) a 1.1(.1)a
11.75(.85) a 10.3(.45) a
81.8(2.65) a 86.0(2.85) a


C. odorata T.grandis
7(.2) aa
6.4(.95) ab
46.4(7) bb
.9(.35) aa
9.7(1.9) ba
88.6(2.45) ba















ACKNOWLEDGMENTS

I would like to thank my parents, Mr. Jorge Garcia and Mrs. Juanita Garcia, for

their encouragement throughout the duration of my study. I would like to especially

thank my mother for teaching me that patience and courage are big attributes toward

achieving one's goals in life; she believed in me from the beginning.

I would like to thank my adviser, Dr. Shibu Jose, and my committee members, Dr.

Michael Bannister and Dr. Richard Stepp, who guided me throughout the duration of my

study. I could not have done this without the help of the staff in the School of Natural

Resources and the Environment, and, to them, I am grateful. I would also like to extend

sincerest gratitude to my husband, Mr. Pio Saqui, for his patience, words of

encouragement, and for keeping me on tract. I would also like to acknowledge the

assistance of Dipl. Ing. Sylvia Baumgart, Project Manager/Coordinator OAS Agro-

Forestry Research Project, for providing technical assistance while I was in the field. You

all made my life and my studies easier at the University of Florida.









Cadish, G., Ndufa, J.K., Yasmin, K., Mutuo, P., Baggs, E., Keerthisinghe, G., and
Albrecht, A., 2002b. Use of stable isotopes in assessing belowground contributions
to N and soil organic matter dynamics in: International union of soil science, the
soil and fertilizer society of Thailand, Ministry of agriculture and cooperatives of
Thailand (eds) 17th World Soil Science Conference 'Soil Science: confronting new
realities in the 21st century'. International soil science society, Bangkok, Thailand,
CD-Paper No.1165, pp. 1-10.

Cannel, M., Van Noordwijk, M., and Ong C., 1996. The central agroforestry hypothesis:
The trees must acquire resources that the crop would not otherwise acquire.
Agrofor. Sys. 34, 27-31.

Chapin S.F., Matson, P.A., Mooney H.A., 2002. Principles of ecosystems ecology.
Springler-Verlag, New York.

Cornelius J.P., Watt A.D., 2002. Genetic variation in a Hypsipyla-attacked clonal trial of
Cedrela odorata under two pruning regimes. Forest Ecology and Management 183,
341-349.

Conklin, H. C., 1957. Hanunoo Agriculture: A Report of an Integral System of Shifting
Cultivation in the Philippines. Rome: United Nations Food and Agricultural
Organization.

Cogger C., 2000. Soil Management for Small Farmers. Farmers West of the Cascade
Series. Food and Farm Connection. Pp 1 24.

Coolman, R.M. and Hoyt, G.D., 1993. Increasing sustainability by intercropping.
HortTechnology, 3, 309-312.

Cusack, D. and Montagnini F., 2004. The role of native species plantations in recovery of
understory woody diversity in degraded pasturelands of Costa Rica. Forest Ecology
and Management 188, 1-15.

Dinesh, R., Ghoshal Chaudhuri, S. Ganeshamurthy A.N., Chanchal D., 2003. Changes in
soil microbial indices and their relationships following deforestation and cultivation
in wet tropical forests. Applied Soil Ecology 24, 17-26.

Dommergues, Y.R., Subba Rao, N.S., 2000. Introduction ofN2-fixing trees in non-N2-
fixing tropical plantations. In: Subba Rao, N.S., Dommergues, Y.R. (Eds.),
Microbial Interactions in Agriculture and Forestry, vol. II. Science Publishers,
Enfield, NH, USA, pp. 131-154.

Dunisch, O., Montoia, V.R., Bauch J., 2003. Dendroecological investigations on
Swietenia macrophylla King and Cedrela odorata L. (Meliaceae) in the central
Amazon. Springer-Verlag. Trees 17, 244-250









surmised that the two species are coexisting probably because their niches do not overlap

sufficiently for them to become competitive.

This research did not investigate the sociological component but it is imperative

that we recognize that an agroforestry system cannot operate without farmers. Farmers

are a rural population; they produce for themselves but also produce for the markets.

Their economy depends on family labor but they often employ themselves and employ

others as needed. Therefore, as rural producers they are an important social category of

contemporary societies and need to be recognized especially by the political authorities

who control the economic and development policies in rural area (Nettings, 1993).









taxonomic groups is expected to be less affected by insect pests than a system composed

of closely related species as in a monoculture system (Vandermeer, 1989).

Under natural conditions, even insects with a limited host range have been

observed to feed on taxonomically diverse species of plants. In a mixed species system,

therefore, the plants assembly should consist of species that do not double as host for

insect pests of other plants in the system whether crops or woody perennials. Some

insects utilize different host plants as food in their larval stages from those eaten in the

adult stage. So an even greater range of plants in a mixed species system may be attacked

by different stages of an insect pest.

If all or most plants in a mixed system are palatable to a polyphagous pest, then it is

likely that the insect will stay longer and become more numerous, causing greater

damage. Therefore, monophagous pests can be controlled altogether by not including

their host plants in the system. The host range of oligophagous pests can also be

narrowed by eliminating palatable species form the assemblage and replacing them with

non-host plants. Therefore what's important to remember is that farmers need to be

knowledgeable about such pest relationships in order for them to be able to make

informed choices when preparing their fields.

There are two existing hypothesis proposed initially by Aiyer (1949) and redefined

later by Root (1973) and proposed as three hypothesis by Vandermeer (1989) in reference

to the presence of pest in an area; (1) the disruptive crop hypothesis in which a second

species disrupts the ability of a pest to efficiently attack its proper host (specialist

herbivore) (2) the trap crop hypothesis in which a second species attracts a pest that

would normally be detrimental to the principle species (generalist herbivore) (Hokkanen,









In the mixed species system under investigation the C. odorata trees suffered a lot

of damage from the H. grandella larvae attack. This was as a result of intercropping S.

macrophylla and C. odorata in the same plot at the same time since both trees are host for

the H. grandella. Furthermore, this plot is at the edge of a natural forest where other

mature C. odorata and S. macrophylla trees are growing. Therefore, there is a potential

source of food which keeps the larvae present throughout the year in this treatment. On

the other hand the monoculture treatment is located about 200 meters away from the

mixed species treatment and the land around it has been cleared. Therefore, there are no

mature C. odorata trees in their vicinity. Furthermore, this plot was established leeward

from the mixed species plots.

So what are the implications for farmers today? There are several positive findings

that will aid farmers in their decision to continue or to start farming using mixed species

systems. Montagnini (1994), Montagnini et al. (1995), Parrota (1999) and Jose et al.,

(2006) have shown that mixed species systems are not only good for the environment, but

can be economically better than monocultures.

Farmers need to contact the experts at the Agriculture and Forestry department in

their home country and also the leading experts in research such as the Universities or

other local NGOs who can provide support and advice in the planning and preparation of

their fields. According to Vandermeer (1989) the basic structure of a plantation imposes

certain inevitable microhabitat features at level of the ground. It is through an analysis of

these necessary features that we can gain an idea of how the system should be designed to

eliminate competition between species which might require the same resource at the same

time for their growth. On the other hand plants or crops which are host to polyphagous



































To my mother Mrs. Juanita Garcia, You Are My Star.









thereby reducing the monetary input into establishing and managing these mixed species

systems.

In order for mixed species production systems to become an important land use

practice in Belize, the farmers have to be convinced about the benefits of these systems.

Scientific evidence is now available to show that the spatial and temporal heterogeneity

created by the mixed species plantings can help enhance resource availability and

capture, increase production, reduce risk of intensive agricultural and forestry practices,

and achieve system stability and sustainability (Lefroy et al., 1999; Nair, 2001). Mixed

species plantations also yield more diverse forest products than monoculture stands,

helping to diminish farmers' risks in unstable markets. Lastly mixed species cropping

could also be an important tool for pest and disease management in agriculture or farming

systems as has been shown by studies done by Morales and Perfecto (2000) in

Guatemala; Montagnini et al. (1995) in Costa Rica; and by Kelty (2006) and Risch et al.

(1983) who reviewed published articles on mixed species systems and pest management.

Unfortunately, there is no documentation on the performance of mixed versus

monoculture systems for popular species in Belize. Therefore it is not likely to be widely

adopted by commercial farmers until the potential benefits have been fully evaluated and

can be shown to outweigh those of the monoculture systems.

Study System

This study examined the growth and soil chemical properties of mixed and

monoculture plantations of C. odorata and T. grandis in Belize. We hypothesized that

C. odorata and T grandis trees growing in mixed species treatment will
produce more volume than in monoculture treatment;

survival and growth of selected tree species will be better in mixed-species than
in monoculture treatment;









Mixed species systems have been investigated as a strategy for pest control.

Although the results are inconclusive in our trial, based on the literature it can be said

with some certainty that mixed species systems do reduce pests in most instances. More

research is needed to point to the exact process involved in this strategy. Several studies

have shown a decrease in pests when crops are intercropped when compared to

monocultures. The most outstanding element in this is the fact that the farmer minimizes

risks when using mixed species systems.

Mulch can be produced from leguminous trees within a mixed species treatment.

This mulch which is sometimes referred to as green manure or green fertilizer can be

placed strategically at the base of the plants that are being cultivated and allowed to

decompose to be recycled back into the system. The decomposition of the mulch would

release the nutrients within the mulch and make it available for plant uptake. Hence,

natural fertilizer is added to the system without the fear of pollution. Therefore, this not

only is economically better, but ecologically viable and sociologically sound since the

soils and waterways remain clean. Furthermore, the produce is also free of synthetic

fertilizers and chemicals.

More organic matter means healthier soils and healthier soils means better yield.

The recycling of organic matter occurs in a cycle. Leaves are shed from the trees or

crops and are broken down by the organism in the soil. These organisms then recycle the

nutrients within the soil through excretions and also when they die and decompose.

These nutrients are then taken up by the plants which use them and return them to the soil

as litter fall. The organisms then go through the same process making the nutrients

available for plant uptake. Therefore, it must be stressed that a fertile soil is very









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Temples; Conservation and Development in the Maya Forest of Belize, Guatemala
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polyphagous predators in carrot fields in relation to carrot fly (Psila rosae (F)
(Dipt., Psilidae)) damage. Journal of Applied Entomology.

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to Achieve Sustainable Forest Management. For delivery at: UNFF
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Management. New Zealand.

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Review, 88, 131-137.















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 ............................................... .. ......................... ..

H history of A groforestry .... .......................................... ............. ............................. ..
Role of Agroforestry .............. .. .. .... ...... .......... ........ ............. ....
M onoculture Systems vs. M ixed Species Systems................................. ...........7
Ecological basis for mixed species systems .............................................9
M ixed canopy ............................................................ ......... 10
D eeper rooting system ....................... ............................... ............... 10
Im proving soil quality .............................. ........ ................. .... .......... 11
Available light ........... ................. ........................... ... ........ 13
Mixed species system as a pest management strategy ..............................14
Current Proj ect..................................... ................................ .......... 16

2 GROWTH RATE OF TECTONA GRANDIS AND CEDRELA ODORATA IN
MONOCULTURE VERSUS MIXED SPECIES PLANTATIONS IN BELIZE ......18

Problem Statm ent ......... .... .......... ...... ....... .. ................. ..... ... ... 19
Mixed Species Systems in Belize...... ...................... ...............20
Study System .............................................22
Characteristics of Cedrela odorata and Tectona grandis .................................23
M materials and M methods ....................................................................... ..................23
Study Area .................. ...... ..... .................. 23
Experimental Design and M easurements .................................... .................24
Statistical A analysis .......................... .......... ............... .... ..... .. 26
R results A nd D discussion ........... ................................ ............. ............... 26
Survival Rate of T. grandis and C. odorata ................................. ............... 26
G row th ............ .................................................... ............. .27
F oliar N utrients...............................................................29
Soil Fertility ........................................... ...................... ........ 30


v









interaction may occur such as the case when trees prevent soil erosion, and deep roots

prevent soil nutrient leaching from the system (Vandermeer, 1989).

Mixed canopy

According to Gathumbi (2004) a mixed species system can have a denser canopy

than that of a monoculture system when different species occupy different canopy

positions and levels, allowing it to capture light that would otherwise be inefficiently

utilized in monoculture systems (Morales and Perfecto, 2000; Kelty, 2006). Mixed

canopy may also reduce weed competition, by reducing incident light on the forest floor

making the plant unable to photosynthesize and eventually die. It can also reduce water

loss by evaporation directly from the bare soil, with the use of cover crops leaving more

water for productive transpiration. Furthermore, evaporation of transpired water or

precipitation intercepted by the canopy may further contribute to understory temperature

reductions (Huxman and Smith, 2001; Unwin et al., 2006) and the formation of

microclimates suitable for other organisms in this way providing habitat for organisms

(Ruark et al., 2003).

Deeper rooting system

A mixed species system may also have a denser and perhaps deeper rooting system

allowing maximum use of soil, thereby increasing the potential for water and nutrient

uptake (because different species may use different soil depths) (Akinnifesi et al., 1996;

Morales and Perfecto, 2000). Coupled with better soil physical properties and the

reduction of runoff it may conserve water, leading to enhanced soil biological activity

and nutrient cycling. Through this process it increases the availability of nutrients which

can be readily absorbed by the plant roots at different soil levels since plant roots obtain

most of their nutrients from the soil solution (Holcomb, White and Tooze, 1982; Smith et









Liebman, M.Z., 1986. Ecological Suppression of Weeds in Intercropping Systems:
Experiment with Barley, Pea, and Mustard. PhD Dissertation, Berkeley, California.

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epigeic earthworms under different deciduous forest litters decomposition
Bioresource Technology 88, 197-206.

McGrath D., 1987. The Role of Biomass in Shifting Cultivation. Human Ecology 15,
221-242.

Mead, R., and Willey, R., 1980. The concept of a land equivalent ratio and advantages in
yields from intercropping. Exper. Agric. 16, 217-228.

Medhurst J.L., Pinkard E.A. Beadle C.L. Worledge D., 2006. Photosynthetic capacity
increases in Acacia melanoxylon following form pruning in a two-species
plantation. Forest Ecology and Management 233, 250-259

Montagnini, F., 2000. Accumulation in above-ground biomass and soil storage of mineral
nutrients in pure and mixed plantations in a humid tropical lowland. Forest Ecology
and Management 134, 257-270

Montagnini, F., Guarigauata, M., Ribeiro N., Mariscal A., 1999. Regeneracion natural en
plantaciones puras y mixtas de species natives. Actas IV Semana Cientifica,
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economics of swidden agriculture. Ambio 26, 118-123.

Montagnini, F., Gonzalez, E., Rheingans, R., Porras, C., 1995. Mixed and pure forest
plantations in the humid neotropics: A comparison of early growth, pest damage
and establishment costs. Commonwealth For. Review 74, 306-314.

Montagnini, F., Sancho, F., 1994. Above-ground biomass and nutrients in young
plantations of four indigenous tree species: implications for site nutrient
conservation. J. Sustainable For. 1, 115-139.









monoculture. An investigation to compare soils in both systems revealed that the mixed

system improved soil fertility (higher cation exchange capacity) compared to the

monoculture treatment. Future research should examine soil and canopy nutrient

dynamics in detail so that the underlying mechanisms for the observed yield advantage in

mixed species system can be unveiled.









the production systems in the future (Brondizio and Siqueira, 1997). Hence the

management strategy should be one that will allow the intensive use of the system

without depletion of it nutrients via the use of leguminous trees and proper draining

systems.

If mixed species type of agroforestry is practiced properly, it can be

environmentally sound, ecologically viable, sociologically acceptable and economically

feasible. Mixed species agroforestry is not a new form of agriculture in Belize C.A. It has

been practiced perhaps for centuries by the indigenous people. For example, the Maya

have used this form of agriculture in cultivating their crops while also producing timber

and non-timber forest products, including medicinal plants (Levasseur and Olivier, 2000).

Agroforestry has also been used in the form of home gardens where several species are

grown together (Levasseur and Olivier, 2000; Steinberg, 1998).

One of the agroforestry systems receiving much attention presently is the mixed

species forest plantations (Jose et al., 2006). Mixed species plantations offer multiple

market and non-market commodities or benefits such as food, fodder, timber, carbon

sequestration, and soil enrichment among others.

Monoculture Systems vs. Mixed Species Systems

Monoculture systems have been traditionally used globally to increase productivity.

However, pollution due to over fertilization has created great interest in finding ways to

decrease the amount of fertilizers being used in agricultural systems. Monoculture

systems also lead to soil degradation because of over use and extensive mechanization of

farming techniques. Pests have also been a major challenge in monoculture systems

which require a vast amount of pesticides that makes the safety of the items produced

questionable and also leads to contamination of water resources (Bruntland, 1987).









overall results indicate that the survival rate of trees in the mixed species treatment was

better than those in the monoculture treatment.

Growth

T. grandis grown in mixed species system had greater growth increment (Figure

2-3) compared to monoculture during 2005 and 2006 (Figure 2-4). Similar growth

pattern was recorded for GLD and SVI. Height and GLD of T. grandis at the end of the

growing season in 2006 showed significant differences (p<0.0001) between the

monoculture and mixed species systems. T. grandis trees in the mixed species plots were

40% taller than those in the monoculture plots. Again, similar patterns were observed for

both GLD and SVI. For example, SVI of T. grandis in mixed species system was 0.91

m3 per ha. compared to 0.49 m3 per ha in monoculture (Table 2-1).

Height increment of C. odorata was significantly different between the

monoculture and mixed species systems as depicted by the different letter in Figure 2-3

and 2-4. The growth rate of the C. odorata trees was better than that experienced by the

trees in the mixed species system. Height increment in the mixed species system was

impacted mostly by a shoot borer, H. grandella, which attacked the leading shoots

(Cornelius and Watt, 2002), which had to be pruned regularly. GLD, however, was

greater in the mixed species system compared to monoculture. It was noted that the most

growth occurred during the beginning of the growing season (wet/rainy season). The

growth pattern observed was similar to what Worbes (1999) found in Venezuela in a

study done on T. grandis and C. odorata among other tropical trees and by Dunisch et al.

(2002a) and Dunisch et al., (2003) in studies done in Central Amazon on the growth

increment of C. odorata.





























2007 Juanita Garcia-Saqui











Table 2-1. Stem volume index of T. grandis and C. odorata in mixed species system
compared to those in monoculture systems, four years after planting in the
Cayo District, Belize. Differences among treatments are statistically
significant when followed by a different letter using Duncan's test to note
statistical difference (p<0.05).
Treatments SVI (m3/ha)

T grandis C. odorata

Monoculture system 0.4999257 a 0.146872 a

Mixed species system 0.9100141 b 0.1656123 a









Conclusion

The results obtained during this research have led to the conclusion that when C.

odorata and T grandis are grown in mixed species systems with leguminous trees they

have the capacity to produce a higher yield compared to monoculture treatment.

Although we did not measure litterfall which should have given an indication of exactly

how much litterfall occurred in both systems it was evident that there was efficient

cycling of nutrients in the mixed species system because of the higher soil C.E.C in the

mixed species system compared to the monoculture plot. Similar results have been

obtained by several researchers who have investigated similar treatments in the tropics

(Binkley et al., 2003; Montagnini, 2000; Stanley and Montagnini, 1999; Parrotta, 1999)

in which they found that mixed species systems produce a more complex array of

litterfall releasing nutrients back to the soil at different rates because of the composition

of the leaves. Therefore, mixed-species plantations have the potential for out-producing

monocultures, but actual yields depend on soils, silviculture, and species. It is important

to know more about these interactions to provide a solid foundation for mixed-species

management of plantations (Binkley et al., 2003; Dommergues and Subba Rao, 2000).

It was expected that the presence ofL. castilloi and S. panamensis, both N2-fixing

trees and the cover crop A. pintoi, would result in higher productivity of T grandis and

C. odorata because of their ability to fix nitrogen and make it available for the trees.

However, these expected effects could not be ascertained because of the limited foliar

and soil analysis data. However there was a tendency of higher yields per plant in the T

grandis and C. odorata associated with L. castilloi and S. panamensis than in the

monoculture system, possibly due to an indirect effect of nitrogen fixation by the

leguminous trees. Based on the growth recorded throughout the study period it can be















GROWTH RATE OF TECTONA GRANDIS AND CEDRELA ODORATA IN
MONOCULTURE AND MIXED SPECIES SYSTEMS IN BELIZE, CENTRAL
AMERICA

















By

JUANITA GARCIA-SAQUI


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


2007









were not different between the two treatments. The higher growth observed in T grandis

could be a result of the higher CEC in the mixed species plot (Table 2-3).

Higher soil fertility in mixed species systems compared to monocultural systems

has been reported in other studies done in Puerto Rico by Parrotta (1999), and also in

Costa Rica by Montagnini (2000). They found that soil fertility was higher in mixed-

species plantations of Strephnodendron microstachyum, Vochysia guatemalensis,

Jacaranda copaia and Callophylum brasiliense than in pure stands of C. brasiliense and

V. guatemalensis. Stanley and Montagnini (1999) obtained similar results in a study on

nutrient accumulation in pure and mixed plantations in Costa Rica. This implies that

there is perhaps faster nutrient cycling and turnover in mixed species systems than in

monocultures, making the soil fertility higher in the former. It is also possible that the

mixed species system has a better nutrient use efficiency. As suggested by Jose et al.

(2006) and Binkley et al. (1997), in a mixture of species, each with different nutrient

requirements and different nutrient recycling properties, there may be overall less

demand for on site nutrients because of the niche separation. This means that each plant

utilizes the resources at a different stage in their life cycle or at different rates. On a

study done by Stanley and Montagnini (1999) in plantations of mixed versus

monoculture, the mixed plantations had intermediate values of soil N, P and K, but lower

soil Ca and Mg relative to pure plantations which was similar to those obtained in this

experiment. It is possible that Ca and Mg are removed from the soil and stored in the

plant biomass during the active growing season, and are subsequently removed when the

plants are harvested.









(Vandermeer, 1989; Brady and Weil, 2002). This means that these nutrients can be

immobilized and become unavailable for plant uptake. However if the soil is fertile

allowing organisms to live within it, they can break down those minerals and make them

available for plant uptake (Brady and Weil, 2002; Mooney et al., 2002).

According to Ruark et al. (2003) three main tree-mediated processes have been

identified through research which determines the extent and rate of soil improvement in

mixed species systems. These are 1) increased N input through biological nitrogen

fixation by nitrogen-fixing trees, 2) enhanced availability of nutrients resulting from

production and decomposition of substantial quantities of tree biomass, and 3) greater

uptake and utilization of nutrients from deeper layers of soils by deep-rooted trees (Nair

et al., 1999).

In addition, a mixture of species, each with different nutrient requirements and

different nutrient recycling properties, may be overall less demanding on site nutrients

than pure stands because of their niche separation (Binkley et al., 1997; Jose et al., 2006).

This indicates that the trees are using the nutrients in different proportions and during a

different time period in their growth patterns. In a study of mixed versus monoculture

plantations in Costa Rica, Montangnini et al., (1995) and Montagnini and Porras (1998)

found that the growth of dominant species was faster in mixed than in pure plantations,

and that mixed plantations had high volume and biomass production in comparison with

pure stands. In another study, the mixed plantations had intermediate values of soil N, P

and K, but lower soil Ca and Mg relative to pure plantations (Stanley and Montagnini,

1999) which supports the fact that nutrients are used differently throughout a mixed









Vandermeer (1989) suggests that the LER measurement takes its name from its

interpretation as relative land requirements for mixed species versus monocultures.

Therefore, what we are looking at is whether the monoculture plots are producing the

same amount of biomass as the mixed species systems or vice versa. If the LER is greater

than 1.0 then the mixed species system is more efficient. If it is less than 1.0 then

monocultures are more efficient systems of production of the hardwood trees.

Foliar Nutrients

According to Goncalves et al. (1997), Montagnini and Sancho (1994), Foelster and

Khanna (1997), soil nutrients may be generally abundant early in stand growth as a result

of low plant uptake, stimulation of nutrient mineralization, and low immobilization in

plant biomass, but as plantations grow, decreased nutrient availability can result from

immobilization into woody biomass and detritus pools, and decreased mineralization

(Binkley et al., 1997; Foelster and Khanna 1997; Wadsworth 1997). Therefore,

alternatives to conserve site nutrients may include preferential planting of tree species

that do not place high nutrient demands on the site (Bruijnzeel, 1984; Wang et al., 1991;

Montagnini and Sancho, 1994). Information available is usually on the effect of trees on

monoculture systems while the effect of different trees on mixed species system is

minimal.

Table 2-2 shows the range in concentration in the leaf for the elements N, P, K, Ca

and Mg observed during the research. However, there is insufficient data to evaluate the

treatment differences in leaf composition for these elements in T. grandis and C. odorata.

Although limited samples prevented a statistical comparison, it appears that there is more

calcium, magnesium and nitrogen in the leaves of the C. odorata in the mixed species

plots than those of the monoculture plots (Table 2-2). The higher nitrogen may be due to









Dunisch O, Bauch J, Gasparotto L., 2002a. Cambial growth dynamics and formation of
increment zones in the xylem of Swietenia macrophylla King, Carapa guianensis
Aubl., and Cedrela odorata L. (Meliaceae). IAWA J 23, 101-119.

FAO, 2001. Global Forest Resources Assessment, 2000, Main Report. FAO Forestry
Paper No. 140, Rome.

FAO, 1997. State of the World's Forests 1997. Food and Agriculture Organization of the
United Nations, Rome, Italy, 200 pp.

Finch S; Collier R., 2000. Host-plant selection by insects a theory based on
'appropriate/inappropriate' landings by pest insects of cruciferous plants.
Entomologia Experimentalis et Applicata 96, 91-102.

Folster, H., Khanna, P.K., 1997. Dynamics of nutrient supply in plantation soils. In:
Nambiar, E.K.S., Brown, A.G. (Eds.), Management of Soil, Nutrients and Water in
Tropical Plantation Forests. ACIAR/CSIRO/CIFOR, ACIAR, Canberra, Australia,
pp. 338-378.

FRA, 2000. Annotated Bibliography Forest Cover Change Belize. Forest Resources
Assessment Programme. Working Paper 40 Rome, 2000.

Gathumbi, S.M., 2004. Root recovery of five tropical tree and shrub species by sieves of
different mesh sizes. Agrofor. Sys. 60, 233-237

Gholz, H.L, 1987. Agroforestry: Realities, Possibilities and Potentials. Dordrecht:
Martinus Nijhoff Publisher.

Goncalves, J.L.M., Barros, N. F., Nambiar, E.K.S., Novais, R.F., 1997. Soil and stand
management for short-rotation plantations. In: Nambiar, E.K.S., Brown, A.G.
(Eds.), Management of Soil, Nutrients and Water in Tropical Plantation Forests.
ACIAR/ CSIRO/CIFOR, ACIAR, Canberra, Australia, pp. 379-417.

Government of Belize, 1996. Belize Abstracts of Statistics. Central Statistical Office,
Ministry of Finance, Belmopan, Belize.

Guillet D., 1987. Agricultural Intensification and Deintensification in Lari, Colca Valley,
Southern Peru. Pg 201-224 in B. Isaac (ed.) Research in Economic Anthropology
Vol.8 Greenwich, Ct. JAI Press.

Harrison, P., Mattos, M. and Uhl C., 1995."A profile of palm heart extraction in the
Amazon estuary." Human Ecology: An Interdisciplinary Journal 23, 357-385.

Hiremath, Ankila J., Ewel, John J., and Cole Thomas G., 2002. Nutrient Use Efficiency
in Three Fast-Growing Tropical Trees. Forest Science 48, 662-672.

Hiebsch, C., and McCollum, R., 1987. Area-X-time equivalency ratio: A method for
evaluating the productivity of intercrops. Agron. J. 79, 15-22






17


interactions when species are mixed together. The following chapter describes the study

in detail.









C o n c lu sio n ................................................................................. 3 2

3 CONCLUSIONS AND RECOMMENDATIONS................................................41

L IST O F R E F E R E N C E S ...................................... .................................... ....................47

B IO G R A PH IC A L SK E T C H ...................................................................... ..................56









also been extracted for domestic and export uses. However, C. odorata is the preferred

hardwood species domestically and has become scarce (GOB, 1996; Primack et al.,

1997).

As logging becomes unproductive, there is a shift towards agriculture, which leads

to increased negative impacts such as deforestation and soil degradation. This keeps

exerting pressure on forest managers and scientists to seek alternative ways to meet

demands for timber. The demand for timber is projected to increase consistently. One

promising alternative to increase timber production is agroforestry in the form of mixed

species systems.

Mixed Species Systems in Belize

Traditionally C. odorata (Cedar) and leguminous trees (i.e. Lonchocarpus castilloi

(Black cabbage bark) and Sweetiapanamensis (Billy Webb)) grow naturally in the sub-

tropical forests of Belize. A more recent timber species of choice is Tectona grandis

(Teak). These tree species are now being incorporated into agricultural farming systems,

for purposes other than timber production such as protection against soil erosion, nutrient

cycling, and shade. Similarly, cash crops varieties such as hot peppers and papayas are

intercropped in these systems. However, when these trees are grown in managed mixed

species agroforestry systems (Nair, 1984), especially in plots that includes other

leguminous plant species such as Lonchocarpus castilloi (Black cabbage bark) and

Sweetiapanamensis (Billy Webb) and ground cover crops such as the perennial Arachis

pintoi (pinto peanut), competition for essential nutrients and sunlight may be less severe

than in monocultures because of the niche separation (Vandermeer, 1989; Jose et al.,

2006).









Height and ground line diameter (GLD) were measured on a weekly basis from

May through August in 2005 and in August 2006. Tree height was determined using a

height pole, while diameter was measured with a digital caliper. Stem volume index

(SVI) was then calculated using the following formula: SVI=GLD2 x height.

Volume yield of monoculture and mixed species plantations was compared using

the Land Equivalent Ratio (LER) using the following formula:

LER = SVI C. odorata (mix) / SVI C. odorata (monoculture) + SVI T grandis

(mix) / SVI T. grandis (monoculture).

The LER is the ratio of the area needed under monoculture to a unit area of intercropping

at the same management level to give an equal amount of yield. Therefore it compares

the performance in intercrop to the performance in monoculture of a particular species;

i.e., in this case T.grandis and C.odorata in mixed versus monoculture systems.

Soil samples (0-15 cm) were collected from the mixed-species and the monoculture

plots twice (2005 and 2006), but data were pooled since no differences were found

between years. Soil samples from the mixed species plot appear as one soil because the

soil was taken from the plot consisting of both trees. Soil samples were processed by air

drying overnight, removing root parts and large stones, and crushing remaining soil until

finely ground. Samples were analyzed for organic matter, pH, CEC, K, Ca and Mg

content. Ca, K, and Mg were extracted using neutral normal ammonium acetate, and

analyzed by atomic absorption spectrophotometer. Soil pH was measured in a 2:1 soil:

water slurry made with deionized water. Organic matter was analyzed by

dichromate/colorimetric method while Cation Exchange Capacity was calculated from









available for photosynthesis diminishes as it moves from the canopy to the lower layers

of the system.

Mixed species system as a pest management strategy

There are many studies on the effect of intercropping on pest attacks. Although

studies abound, they are often contradictory due to the difficulty of pointing out the

ecological factors that can affect insect-plant relations (Kelty, 2006; Ramert et al., 2002).

In one of his studies Andow (1991) analyzed 209 studies involving 287 pest species on

mixed species system versus monocultures. When compared with monocultures, the

population of pest insects was lower in 52% of the studies (149 species) and higher in

15% (44 species). The population of natural enemies of the pests was higher in the

intercrop in 53% of the studies and lower in 9%.

In another study conducted in the Organization of American States (OAS) funded

project site in Belize it was determined that there were more pest attacks in the hot pepper

monoculture plots than in the mixed species plot (Imhof, 2004). The results of such

studies therefore imply a complex situation in which the specific agro-ecological

situation is important. However, in order to develop mixed species cropping as a tool it is

necessary to understand the underlying mechanisms involved.

Plants belonging to the same or a very close taxonomic group have the tendency to

share common pests. In agroforestry systems, aligophagous and polyphagous insect pests

are expected to thrive if both components belong to the same or a closely allied

taxonomic group. An insect feeding on a plant with a certain biochemical make-up will

adapt more easily to closely related plants with similar biochemical constituents than to

species that have entirely different constituents because of taxonomic differences. A

mixed species agroforestry system comprised of plant species belonging to different














CHAPTER 1
INTRODUCTION

Belize, a Central American country, with a population size of -290,000, is located

to the south of Mexico, east of Guatemala and bordered to the east by the Caribbean Sea.

It lies between 15045' and 18030' N latitude, and 87030' and 89015' W longitude. The

total land area is 22,960 sq km (8,867 square miles) of which 95% is located on the

mainland and 5% is distributed over more than 1060 islands. Total national territory

(including territorial sea) is 46,620 sq km (approximately 18,000 square miles) (FRA,

2000). This strategic geographical location allows Belize to be considered part of the

Caribbean economy and also integrated within Central America. The location and long

history of peaceful existence attracted an influx of Central American immigrants

(Latinos) throughout the 1980s and at a reduced rate after the mid 1990s until the present

(Zisman, 1996; Barry and Vernon, 1995).

The displaced immigrants have settled mostly in the rural areas and are now in the

forefront of local small scale agricultural production. They mostly produce vegetables

and short-term cash crop. In their quest to produce enough agricultural products, the

Latinos (also known as Mestizos) are using an intensified mode of slash and burn

agriculture, which has harmful effects on the natural environment.

The harmful effects of an intensified mode of slash and burn can be noted, firstly

by the land being cultivated repeatedly without allowing for adequate fallow periods.

Secondly, the agricultural system is being used for monoculture agricultural crops,

instead of mixed species systems (Arya and Pulver, 1993). Logically, the reasons for such









the cation results. All analyses were performed at a commercial lab (A & L Southern

Agricultural Laboratories, Inc., Pompano, Florida).

Leaf samples were also collected during the first year for foliar chemical analyses.

The foliar tissue samples were first washed and oven dried (750C) for 48 hr. The dried

tissue samples were ground in a Wiley Mill. Foliar samples were digested by a wet

ashing procedure using sulfuric acid and hydrogen peroxide. The digest is then filtered

and fractioned. The different elements were analyzed using atomic absorption and UV-

Visual Spectroscopy (Wolf, 1982). All analyses were performed at a commercial lab (A

& L Southern Agricultural Laboratories, Inc., Pompano, Florida).

Statistical Analysis

Data was analyzed using ANOVA within the framework of a randomized complete

design using SAS. The dependent variables were tested for normality using the Shapiro-

Wilk statistic. Duncan's test was used for mean separation if ANOVA revealed

significant differences at a=0.05.

Results And Discussion

Survival Rate of T. grandis and C. odorata

Survival of trees varied between treatments. Five years after planting, there was a

survival rate of 77 % in monoculture treatment. On the other hand, the survival rate of the

mixed species treatment was a little higher at 80%, considering that most mortality

occurred on the C. odorata trees due to the Hypsipyla grandella Zeller infestation.

Individually, the survival of C. odorata in the mixed species treatment was 75% while

that of the monoculture treatment was 77.5%. The survival of T. grandis in the mixed

species treatment was 85% while on the monoculture treatment it was 77.5%. The















o mono u mixed

3

2.5

2

1.5



0.5

0


2
I -5



1.5






0-
-


1.4

1.2


C.odorata


Figure 2-4. Final height (m), GLD (cm) and SVI (cm3) of C. odorata and T. grandis at four
years after planting in mixed species systems versus monoculture systems at
the study site in Cayo District, Belize. The difference among treatments are
statistically significant when followed by different letter. Error bars represent
S.E of the mean.


a


T.grandis









Furthermore as the cropping system moves from a random mix of plants to a

monoculture, the biodiversity of the system decreases. Eventually, the productivity of the

whole system can decrease (Vandermeer, 1989; Altieri, 1999) because of competition for

resources (Jose et al., 2006).

Mixed species systems of many species on the other hand are better suited for the

environment. The exception to this is the palm trees grown in monoculture systems in the

Amazon. Studies have shown that these palm trees grow better in monoculture systems

than in mixed species systems (Pollak, Mattos, Uhl, 1995). Several studies have

indicated that mixed species systems not only produce as much or even more than

monoculture systems but they also are better able to prevent soil erosion, leaching of soil

nutrients and pollution. Other advantages of mixed species systems are that herbivores

are deterred from finding their hosts, nitrogen is utilized more efficiently and it also

reduces evaporation (Netting, 1963, 1965; Vandermeer, 1989; Smith et al., 1997; Stanley

and Montagnini, 1999; and Cadisch et al., 2002).

Mixed species agroforestry systems may offer three kinds of benefits to farmers.

These are a) increased productivity, b) increased stability and c) increased sustainability.

The first benefit regarding total productivity of yield can be higher (i.e. output of valuable

products) per unit of land through reduced damage by pests and diseases.

There are several mechanisms that need to be studied in order to understand the

advantages of mixed species systems. These mechanisms include advantages of a mixed

canopy, deeper rooting system, improvement of soil quality, pest control, resource

partitioning and sharing. These mechanisms or factors are briefly discussed in the

following sections.














CHAPTER 3
CONCLUSIONS AND RECOMMENDATIONS

It is well known that a mixed species plantation have many advantages for farmers,

among them being that the farmers can grow short-term cash crops and obtain some

annual income while they wait for the long-term benefit from wood production from the

associated trees. However, in the case where C. odorata is being used we must reiterate

that the C. odorata is highly susceptible to the attack of the shoot borer H. grandella

Zeller, which is considered to be one of the most severe forest pests in Latin America and

the Caribbean (Hilje and Cornelius, 2001). On the research site, the C. odorata grown in

the mixed species system is constantly being attacked by the larvae which results in many

branches which makes the tree unsuitable for commercial timber production.

The use of intercropping can be a viable alternative for many farmers. Therefore, it

is very important and necessary that information about the factors that affect or enhance

C. odorata and T. grandis growth is made available to those interested in this system of

production. The current study attempted to do so by investigating the growth rate of C.

odorata and T grandis in mixed and monoculture system to determine which system

produced the highest yield.

Mixed species systems are very important systems that if planned properly can

provide many benefits for the farmers. Based on this research it can be concluded that in

terms of growth rate in height and diameter of C. odorata and T. grandis, mixed species

systems are better than monocultures. In mixed species systems, the layers that are

formed by the tree canopies provide a microclimate of their own.














LIST OF FIGURES


Figure p

2-1 Map of Belize showing project/research site in the Cayo District........................34

2-2 Graphical description of the monthly weather patterns (temperature (C) and
rainfall (mm)) of the study region in Belize during the study period May -
A ugust 2005 and 2006............. .................................................... .. .... .... ...... 35

2-3 The growth increment per month (measured during a 3 months active growing
season in 2005) of C. odorata and T. grandis in mixed species and monoculture
plots at the study site in the Cayo District, Belize. ............................................. 36

2-4 Final height (m), GLD (cm) and SVI (cm3) of C. odorata and T. grandis at four
years after planting in mixed species systems versus monoculture systems at the
study site in C ayo D district, B elize ........................................ ..............................37









Stem volume index (SVI) per ha was also computed and compared (Table 2-1).

The comparison of SVI revealed significant difference between T. grandis in mixed

versus monoculture plots (p<0.0001), but there was no difference between C. odorata in

mixed vs. monoculture plots (p<0.001). The growth rate recorded during this study was

similar to those obtained in other studies for T grandis and C. odorata, despite the H.

grandella attacks in these plots (Montagnini et al., 1999; Parrota, 1999).

The LER for the mixed species system was 1.47, which indicates that there is some

sort of facilitation occurring because of a modification of some environmental factors) in

a positive way by one or both of the species being intercropped. The mixed species

system could be beneficial compared to monoculture plantations of the same species. It

appears that intercropping does not affect the growth rate of C. odorata trees although the

height of the trees in the mixed species plot was severely affected by the H. grandella

attack. However, T. grandis growth was significantly improved as a result of mixing

species. So, overall, mixed species system had higher production potential than

monoculture. This is similar to the findings of other researchers in which they found that

mixed plantations had overall greater growth in the mixed species systems compared to

the monoculture ones (Montagnini et al., 1993, 1995; Montagnini and Porras, 1998)

which can be a result of the leguminous trees intercropped within the system.

According to Vandermeer (1989) if an experimental plot yields an LER greater

than 1.0 it is certainly true that facilitation has been demonstrated in the system. Hence

competition may be minimal, because competition cannot be eliminated totally from such

a system since resources are certainly being used, but possibly from different levels of the

soil column and at different times of their growing period.









the presence of nitrogen fixing trees and the nitrogen fixing cover crop in the mixed

species plots. However, there was more phosphorous and potassium in the leaves of the

C. odorata in the monoculuture plot than in those of the trees in the mixed system plot.

The result for leaves of the T. grandis shows that there is again more nitrogen along with

more potassium in the mixed species plot compared to the monoculture plot. The nutrient

level of phosphorous, calcium and magnesium are the same for trees in monoculture

versus those in the mixed species system.

The mixed species plot has a diverse amount of trees and other crops (hot peppers

and papaya) intercropped annually which would mean that more nutrients are being

utilized in the mixed species plot. However, the results of the foliar analysis indicate that

although there is extraction of the resources through harvest of the crops the mixed

species plot still has overall more available nutrient resources in the mixed species plot

compared to the monoculture plot.

Soil Fertility

Contrary to our expectation, there was no significant difference in soil organic

matter, pH and K between soils of the monoculture C. odorata and the mixed species

treatment. However, there was difference noted in Mg which was higher in the C.

odorata monoculture plot compared to mixed species plot (Table 2-3). Marked

difference in soil CEC between the mixed and the monoculture systems was also

observed with mixed species systems exhibiting higher CEC than monoculture system.

The fact that soils under mixed species had higher CEC perhaps points to the higher soil

fertility in the system.

The soil under monoculture T. grandis had lower CEC, and lower organic matter

compared to the mixed species plot. However, the other nutrients (pH, K, Mg and Ca)









domain, it becomes possible to derive quantitative measures of diversity and intensity

(Behrens et al., 1994).

Role of Agroforestry

Agroforestry has evolved as a conceptual framework in agriculture and forestry

over the last 40 years as an alternative response to rural development projects. However

it has been carried out for centuries worldwide as an agricultural practice. It includes a

countless variety of systems ranging from swidden-fallow to silvopastoral activities. Nair

(1990) reported more than 150 different agroforestry systems in a global inventory

carried out by ICRAF (International Center in Agroforestry) which included traditional

and newly developed systems (Gholz, 1987). The management strategies identified in

these systems that mimics gardening and native vegetation has long provided a

diversified resource pool for Tropical countries. However, it is only until recently that

understanding of native agroforestry systems has come about. Moreover, the main

challenge to these systems has been to find ways to increase surplus production without

exponential increase of labour input, since it is based on progressive management that

incorporates previous unmanaged areas into the resource pool (Rosenberg and Marcotte,

2005; Roosevelt, 1989; Balee and Gelly, 1989).

Mixed species agroforestry illustrates the potential for intensification of this system

when opportunity such as market demand is favorable. Comparative analysis of food

production systems need to integrate a larger array of variables; since intensification

occurs when there is internal population dynamics and opportunities offered by external

sources. Therefore in the use of mixed species systems in which intensification will

occur, this intensification is defined as a dependent variable of sustainability that

accounts for the ability to maintain production over time, without constraining change in









species system hence there is more nutrient availability in a mixed species system than in

a monoculture plot.

Available light

It is common knowledge that the rate of photosynthesis is an increasing function

of the intensity of light, so that the rate of photosynthesis increases rapidly when a low

level of light is elevated and increases slowly when a high level of light is elevated

(Vandermeer, 1989; Chapin et al., 2002). T. grandis produces large broad leaves which

can be dominant and may decrease the amount and quality of light that reaches the plants

at the lower level. Another factor that would affect light penetration is the overlap of

canopies leading to reduced light intensity. However in a system where the trees are

planted at a distance of 5 m to counteract this effect it will not cause a major effect. On

the other hand this canopy effect will also be evident after the trees have grown and their

canopies have overlapped. In young trees (5 years) this effect is not evident because the

canopy formed still has more space to expand without causing negative effects.

Furthermore, the physiological and morphological traits such as differences in root versus

shoot allocation and differences in leaf structure in the trees of the mixed species systems

are also playing an important role in the capture of sunlight and resources at different

levels in the system (Medhurst et al., 2006).

The light intensity filtering through a mixed species system may be sufficient

enough for shade tolerant and C3 plants to grow in the understory. Hence it is easier for a

mixed species system to utilize available solar energy more efficiently than a

monoculture system, especially when careful planning is involved (Vandermeer, 1989;

Chapin et al., 2002; Unwin et al., 2006). However, it must remain clear that light















LIST OF TABLES


Table p

2-1 Stem volume index of T grandis and C. odorata in mixed species system
compared to those in monoculture systems, four years after planting in the Cayo
D district, B elize ................... .. ....................................... 38

2-2 Foliar analysis results per treatment. Chemical characteristics of the leaves from
C. odorata and T. grandis at age four in mixed and monoculture systems in the
study site in the Cayo District, Belize. ......................................... ...............39

2-3 Chemical characteristics of the top soil to 15 cm depth for monoculture and
mixed species systems, Cayo District, Belize. ................................... ........ 40









amount of labor that would be needed in a system with no ground cover crop

(Vandermeer, 1989).

Results from this research indicate that mixed species can provide higher yield.

Many studies done in tropical countries such as Mexico (Primack et al., 1997), Puerto

Rico (Parrota, 1999) and Costa Rica (Montagnini, 1999) and now Belize have indicated

that better growth rate is obtained from trees growing in mixed species systems compared

to monoculture systems. Intercropping of T. grandis and C. odorata with the leguminous

trees and cover crop has shown an increase of volume production in both hardwood trees

in the mixed species systems when compared to those of the monoculture systems

producing an LER of 1.47. This result could lead to important changes in cultivation

practices mainly for growers wishing to produce timber with minimal insecticide and

fertilizer input. When nitrogen fixers used as ground cover are intercropped with other

crops they can help protect the crop from insect pests, enhance the rate of organic matter,

reduce erosion, supply extra nitrogen to the system and decrease the germination and

development of weeds (Coolman and Hoyt, 1993; Ramert, 1995).

There is also a variety of leaf litter or organic matter produced from these systems,

since plants intercropped are different and they may shed leaves that decompose at

different rate thereby making nutrients available during different intervals. This also

means that these soils are hosts to a variety of organisms which are beneficial to the

system as nutrient recyclers. A very important factor is that you minimize the amount of

fertilizers needed to produce your crops. Leguminous trees should also be intercropped

as much as possible to maintain a constant flow of nitrogen through the system.









pest should also be avoided to eliminate or decrease pests, or insect attack to the crops or

trees.

When planning their overstory crop the farmer must take into consideration the

shade effect to the lower level plants. Hence, canopy structure should be considered so

that the system does not produce too much shade for the understory crops. Hence if

hardwood trees are being used they should be trees with different canopy structures. For

example C. odorata produces a canopy with orthotropic branches that form an open

crown, while S. macrophylla produces a closed canopy and T. grandis produces a canopy

that forms an umbrella-like crown allowing the infiltration of sunlight to the understory

plants. A plantation using similar trees would allow enough sunlight to penetrate through

the layers for photosynthesis to occur on the plants at the lower level. Once the effect of

the overstory species is known each species in the understory should then be

characterized with respect to the daily light environment needed for their survival.

Every mixed species system should have a ground cover crop which provides the

first resource for the farmer. Many leguminous crops such as beans, peanuts, peas etc.

can be used as ground cover crops. These plants will provide food for the family and will

also aid in the recycling of nitrogen making it available for plant. A ground cover crop

also protects the soil from erosion and maintains a suitable microhabitat for organisms in

the soil and the same time acting as a filter reducing the time it takes for the residues of

dangerous chemicals to enter the ground water reservoirs thereby allowing the

breakdown by bacteria of these harmful chemical residues. Of much importance also is

the fact the a ground cover crop will reduce or act as a weed control, thereby reducing the









Hilje, Cornelius, 2001. Es inmanejable Hypsipyla grandella como plaga forestal? Manejo
Integrado de Plagas, No. 61. CATIE, Costa Rica, 4 pp.

Hokkanen H., 1991. Trap cropping in pest management. Annual Review ofEntomology
36, 119-138.

Holcomb, E.J., White J.W., Tooze S.A., 1982. A vacuum extraction procedure for N and
K and conductivity evaluation of potted crop media. Commun in Soil Sci. Plant
Anal 13, 879-899.

Huxman, T.E. and Smith, S.D., 2001. Photosynthesis in an invasive grass and native forb
at elevated CO2 during an El Nifio year in the Mojave Desert. Oecologia 128, 193-
201.

Hunt Mark A., Battaglia Michael, Davidson Neil J., Unwin Greg. L., 2006. Competition
between plantation Eucalyptus nitens and Acacia dealbata weeds in northeastern
Tasmania. Forest Ecology and Management 233, 260-274.

Imhof, D. 2004. Integrated Pest Management. Janus Foundation, Belize. 1-48.
(unpublished).

Jose, S., Gillespie, A.R., Pallardy, S.G., 2004. Interspecific interactions in temperate
agroforestry. Agrofor. Sys. 61, 237-255.

Jose, S. Williams, Zamora D., 2006. Belowground ecological interactions in mixed-
species forest plantations. Forest Ecology and Management 233, 231-239

Keys, E., 2005. Market Intermediaries Link Farms to Markets: Southeastern Mexican
Examples. The Geographical Review. Volume 95, 24-46.

King R.B, Baillie I.C, Abell T.M.B, Dunsmore J.R, Gray D.A, Pratt J.H, Versey H.R,
Wright A.C.S, Zisman S.A., 1992. Land Resource Assessment of Northern Belize.
Volume 1.

Kummer D.M. and Turner B.L. II, 1994. The Human Causes of Deforestation in
Southeast Asia. Bioscience 44, 323-328.

Lamberts, M.L., 1980. Intercropping with potatoes. MS Thesis, Cornell University.

Lefroy, E. C., Hobbs, R. J., O'Connor, M. H., and Pate, J. S., 1999. Agriculture as a
Mimic of Natural Ecosystems. Kluwer Academic Publishers, Dordrecht, The
Netherlands. 438pp.

Levasseur, V., and Olivier, A., 2000. The farming system and traditional agroforestry
systems in the Maya community of San Jose, Belize. Agroforestry Systems 49,
275-288.















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 RATE OF TECTONA GRANDIS AND CEDRELA ODORATA IN
MONOCULTURE AND MIXED SPECIES SYSTEMS IN BELIZE, CENTRAL
AMERICA

By

Juanita Garcia-Saqui

August 2007

Chair: Shibu Jose
Major: Interdisciplinary Ecology

This study seeks to understand the importance of mixed species agroforestry

systems in Belize. It investigated the growth patterns of two hardwood tree species:

Cedrela odorata L. (Cedar) and Tectona grandis L. (Teak) grown in mixed-species and

monoculture plots to determine which type of system provides the best growth pattern.

The hypothesis was that hardwood tree species grown in managed mixed-species system

would grow better because of complimentary interactions between species.

The results showed that the hardwood trees grew faster in mixed-species systems

than in the monoculture treatment. However, C. odorata was found to be more prone to

attacks by Hypsypla grandella Zellar (shoot borer) in the mixed species system than in

the monoculture plots, which reduced their height growth when compared to the

monoculture plot. Despite the H. grandella attacks of C. odorata, the mixed species

system had higher land equivalent ratio (LER) compared to the monoculture treatment,

indicating that mixing species was advantageous over growing the species in




Full Text

PAGE 1

GROWTH RATE OF TECTONA GRANDIS AND CEDRELA ODORATA IN MONOCULTURE AND MIXED SPECIES SYSTEMS IN BELIZE, CENTRAL AMERICA By JUANITA GARCIA-SAQUI 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 2007

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2007 Juanita Garcia-Saqui

PAGE 3

To my mother Mrs. Juanita Garcia, You Are My Star.

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iv ACKNOWLEDGMENTS I would like to thank my parents, Mr. Jo rge Garcia and Mrs. Juanita Garcia, for their encouragement throughout the duration of my study. I would like to especially thank my mother for teaching me that pati ence and courage are big attributes toward achieving ones goals in life; she believed in me from the beginning. I would like to thank my adviser, Dr. Sh ibu Jose, and my committee members, Dr. Michael Bannister and Dr. Ri chard Stepp, who guided me th roughout the duration of my study. I could not have done this without the he lp of the staff in the School of Natural Resources and the Environment, and, to them, I am grateful. I woul d also like to extend sincerest gratitude to my husband, Mr. Pio Saqui, for his patience, words of encouragement, and for keeping me on trac t. I would also like to acknowledge the assistance of Dipl. Ing. Sylvia Baumgart Project Manager/C oordinator OAS AgroForestry Research Project, for providing tec hnical assistance while I was in the field. You all made my life and my studies easie r at the University of Florida.

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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 History of Agroforestry................................................................................................2 Role of Agroforestry..............................................................................................6 Monoculture Systems vs. Mixed Species Systems................................................7 Ecological basis for mixed species systems...................................................9 Mixed canopy...............................................................................................10 Deeper rooting system..................................................................................10 Improving soil quality..................................................................................11 Available light..............................................................................................13 Mixed species system as a pest management strategy.................................14 Current Project............................................................................................................16 2 GROWTH RATE OF TECTONA GRANDIS AND CEDRELA ODORATA IN MONOCULTURE VERSUS MIXED SPECI ES PLANTATIONS IN BELIZE......18 Problem Statment........................................................................................................19 Mixed Species Systems in Belize........................................................................20 Study System.......................................................................................................22 Characteristics of Cedrela odorata and Tectona grandis ...................................23 Materials and Methods...............................................................................................23 Study Area...........................................................................................................23 Experimental Design and Measurements............................................................24 Statistical Analysis..............................................................................................26 Results And Discussion..............................................................................................26 Survival Rate of T. grandis and C. odorata ........................................................26 Growth.................................................................................................................27 Foliar Nutrients....................................................................................................29 Soil Fertility.........................................................................................................30

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viConclusion..................................................................................................................32 3 CONCLUSIONS AND RECOMMENDATIONS.....................................................41 LIST OF REFERENCES...................................................................................................47 BIOGRAPHICAL SKETCH.............................................................................................56

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vii LIST OF TABLES Table page 2-1 Stem volume index of T. grandis and C. odorata in mixed species system compared to those in monoculture system s, four years after planting in the Cayo District, Belize..........................................................................................................38 2-2 Foliar analysis results per treatment. Ch emical characteristics of the leaves from C. odorata and T. grandis at age four in mixed and monoculture systems in the study site in the Cayo District, Belize......................................................................39 2-3 Chemical characteristics of the top soil to 15 cm depth for monoculture and mixed species systems, Cayo District, Belize..........................................................40

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viii LIST OF FIGURES Figure page 2-1 Map of Belize showing project/re search site in the Cayo District..........................34 2-2 Graphical description of the mont hly weather patterns (temperature (Co) and rainfall (mm)) of the study region in Belize during the study period May August 2005 and 2006..............................................................................................35 2-3 The growth increment per month (measured during a 3 months active growing season in 2005) of C. odorata and T. grandis in mixed species and monoculture plots at the study site in the Cayo District, Belize...................................................36 2-4 Final height (m), GLD (cm) and SVI (cm3) of C. odorata and T. grandis at four years after planting in mixed species syst ems versus monoculture systems at the study site in Cayo District, Belize............................................................................37

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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 RATE OF TECTONA GRANDIS AND CEDRELA ODORATA IN MONOCULTURE AND MIXED SPECIES SYSTEMS IN BELIZE, CENTRAL AMERICA By Juanita Garcia-Saqui August 2007 Chair: Shibu Jose Major: Interdisciplinary Ecology This study seeks to understand the importa nce of mixed species agroforestry systems in Belize. It investig ated the growth patterns of two hardwood tree species: Cedrela odorata L. (Cedar ) and Tectona grandis L. (Teak) grown in mixed-species and monoculture plots to determine which type of system provides the best growth pattern. The hypothesis was that hardwood tree species grown in managed mixed-species system would grow better because of complimenta ry interactions between species. The results showed that the hardwood trees grew faster in mixed-species systems than in the monoculture treatment. However, C. odorata was found to be more prone to attacks by Hypsypla grandella Zellar (shoot borer) in the mixed species system than in the monoculture plots, which reduced thei r height growth when compared to the monoculture plot. Despite the H. grandella attacks of C. odorata the mixed species system had higher land equivale nt ratio (LER) compared to the monoculture treatment, indicating that mixing speci es was advantageous over growing the species in

PAGE 10

x monoculture. An investigation to compare so ils in both systems revealed that the mixed system improved soil fertility (higher cati on exchange capacity) compared to the monoculture treatment. Future resear ch should examine soil and canopy nutrient dynamics in detail so that the underlying mech anisms for the observed yield advantage in mixed species system can be unveiled.

PAGE 11

1 CHAPTER 1 INTRODUCTION Belize, a Central American country, w ith a population size of ~290,000, is located to the south of Mexico, east of Guatemala and bordered to the east by the Caribbean Sea. It lies between 15' and 18' N latit ude, and 87' and 89' W longitude. The total land area is 22,960 sq km (8,867 square miles) of which 95% is located on the mainland and 5% is distributed over more than 1060 islands. Tota l national territory (including territorial sea) is 46,620 sq km (approximately 18,000 square miles) (FRA, 2000). This strategic geographi cal location allows Belize to be considered part of the Caribbean economy and also integrated within Central America. The location and long history of peaceful existen ce attracted an influx of Ce ntral American immigrants (Latinos) throughout the 1980s and at a reduced rate after the mid 1990s until the present (Zisman, 1996; Barry and Vernon, 1995). The displaced immigrants have settled mos tly in the rural areas and are now in the forefront of local small scal e agricultural produ ction. They mostly produce vegetables and short-term cash crop. In their quest to produce enough agri cultural products, the Latinos (also known as Mestizos) are using an intensified mode of slash and burn agriculture, which has harmful effects on the natural environment. The harmful effects of an intensified mode of slash and burn can be noted, firstly by the land being cultivated repeatedly wit hout allowing for adequa te fallow periods. Secondly, the agricultura l system is being used for monoculture agricultural crops, instead of mixed species systems (Arya and Pulver, 1993). Logically, the reasons for such

PAGE 12

2 hard choices are financial. Monoculture syst ems are deemed to yield financial benefits within short time periods. Lands that are productive are repeatedly used, leading to degraded and almost sterile soil conditions. It is imperativ e that alternative forms of agriculture are designed; those that will allo w the farmers to cultivate the same amount of land, producing a variety of products with less impact on the environment and on the soil. History of Agroforestry Farmers make nutrients, water and sun light available to the plants and animals they nurture, and they do this as simply and efficiently as they can. In intensive agriculture the task is not so much to tap na turally existing resources, but to increase their supply to support more biotic growth, to maintain the proper conditions over longer duration and to replenish and regulate the supply of those elements that are exhausted. Planting several crops together in mixed stands rather than monocropping is an age-old practice, but practiced rarely in modern in tensive agriculture. In addition to multiple products, ground cover crops used in these mi xed systems provide a stratified cover protecting the field surf ace from rain and direct sunli ght that can contribute to soil degradation (Netting, 1993). It is common knowledge that population growth demands an increase of food production and also an increas e in construction material (Ruark, Schoeneberger, Nair, 2003). Boserups The Conditions of Agricu ltural Growth (1965) is the most cited reference on agricultura l intensification. She discusses the process of raising production at the cost of monoculture work at lower effi ciency of labor. Her in fluential work brought an alternative viewpoint to the relationship betwee n population growth and food production, one that questioned the traditi onal, classical-economic approach to agriculture based on the Ma lthusian paradigm. Boser ups model defined population

PAGE 13

3 growth as the independent variable that induces intensificatio n and increases food production. Therefore, it is based on the fr equency that the land is cropped, portraying agriculture as dynamic and rela ted to a broader array of la nd use activities and landscape changes which is also applicable to timber production. Boserups model further relates intensity to frequency of cultivation, pr oposed in five progressive categories of intensification: 1) forest fallow (20 year cycle), 2) bush fallow (6 years), 3) short fallow (1 years), 4) annual cropping (year ly), and 5) multi-cropping (sequential). Therefore, her model takes into considerati on the environment, the use and importance of technology and socio-economic imp acts allowing for the relativ e elasticity, manageability and variability of human societies. This mode of production provides a more optimistic view than that of the Malt husians about human adaptive capacity to population growth and environmental limitations (Brondizio and Siquiera, 1997). Conklin (1957) is also a proponent of in tensification via mixed species systems. In his studies with the Hanunoo agriculture he challenged the simplistic view of subsistence agriculture by showing the comple xity and diversity of crop association and the efficiency of labor input and output yields in these systems. On the other hand Netting (1963, 1965) also showed the efficiency (biol ogical) of intercropping or intensification techniques with his work among the Kofy ar of Nigeria. Nye and Greenland (1960) showed the relationship between soil and shifting agriculture thereby providing a scientific basis for understandi ng the efficiency of shifting agriculture and its impact on soils. From their investigation they concl uded that there was minimal soil loss through this system of cultivation. Therefore these st udies support the fact that intercropping or

PAGE 14

4 mixed species systems form of cultivation is a dynamic land use system with a flexible productive capacity. A study done by Wilken (1987) and late r by Keys (2005) provided a better understanding of traditional agriculture and resource management practices in Mexico and Central America. Wilken was particularly intrigued by the degr ee of specialization developed by small farmers to cope with e nvironmental and sociological limitations of areas that are considered inappropriate for agriculture. On the other hand, McGrath (1987) reviewed the role of biomass in mixe d species cultivation a nd suggested that the use of length of fallow rather than vegetati on-soil complex be used to measure energy input and intensification into this system, since burning might lead to the loss of biomass from the system. Guillets (1987) studies in Peru added to this information by showing that both intensification through mixed speci es and intercropping systems of production and deintensification can occu r simultaneously at the regional or the community level, noting the importance of considering the coex istence of agriculture and other crops (e.g. trees) within a broad scope of land use. The following work led to the emergence of two interdisciplinary approaches. One was identified as Farming System Res earch (Turner and Brus h, 1987) and the other as agroecology (Altieri a nd Hecht, 1990). Farming System Research focuses on technology while agroecological studies ta rget the understanding of ecological relationships within agricultural systems. By their very nature agroecosystems are very manipulable. Both approaches were interested in looking at agricu ltural changes in the context of socioeconomical a nd ecological changes. However, agroecosystems studies

PAGE 15

5 are broadened by a scheme that considers production and technology as well as intensity measures with emphasis on yield and ecological stability. Research on agricu ltural intensification may be summarized under two headings: (1) intensification analysis based on small farm agriculture and resource management, and (2) land use analysis that places agricultu re within a broader spatial and temporal landscape proposing scales of analysis at the local, regional and gl obal levels (Netting, 1963, 1965 and 1993). Nettings (1993) evaluation of the importance and efficiency of small farmer intensive farming is an example of the first trend. He redefines intensification in the light of sustainability and producti vity. His conclusion was that the disruption of small farmer agriculture in fa vor of modern energyintensive technology has recurrently deintensified agriculture and has promoted more extensive land use systems. The second trend of agricultural st udies mentioned resulted from research that integrates approaches and methods of ecological and socioe conomic and landscape ecology. These were deemed necessary due to the need to understand agriculture and economics from a broader, regional scale (Br ondizio et al., 1994; Moran et al., 1994a) and to understand the impact of land use stra tegies in regional-scale processes (Kummer and Turner, 1994; Ojima et al., 1994; Skole et al., 1994). The process of integration ha s resulted from various unifying interests such as the increased demand for food in less developed countries the effects of deforestation on global biogeochemical and hydr ological cycles, and the loss of biological and crop diversity (Ruark et al., 2003; FAO, 2001; Zimmerer, 1996; Watts, 1987). Therefore by mapping processes of human disturbance onto a landscape, translating them to the spatial

PAGE 16

6 domain, it becomes possible to derive quantit ative measures of diversity and intensity (Behrens et al., 1994). Role of Agroforestry Agroforestry has evolved as a conceptual framework in agriculture and forestry over the last 40 years as an al ternative response to rural de velopment projects. However it has been carried out for centu ries worldwide as an agricu ltural practice. It includes a countless variety of systems ra nging from swidden-fallow to s ilvopastoral activities. Nair (1990) reported more than 150 different ag roforestry systems in a global inventory carried out by ICRAF (International Center in Agroforestry) which included traditional and newly developed systems (Gholz, 1987). Th e management strategies identified in these systems that mimics gardening and native vegetation has long provided a diversified resource pool for Tropical countries However, it is only until recently that understanding of native agrofo restry systems has come about. Moreover, the main challenge to these systems has been to find ways to increase surplus production without exponential increase of labour input, since it is based on pr ogressive management that incorporates previous unmanaged areas into the resource pool (Ros enberg and Marcotte, 2005; Roosevelt, 1989; Ba lee and Gelly, 1989). Mixed species agroforestry illustrates the pot ential for intensification of this system when opportunity such as market demand is favorable. Comparative analysis of food production systems need to integrate a larger array of variables; since intensification occurs when there is internal population dynamics and opportunities offered by external sources. Therefore in the use of mixed speci es systems in which intensification will occur, this intensification is defined as a dependent variable of sustainability that accounts for the ability to maintain production over time, without c onstraining change in

PAGE 17

7 the production systems in the future (B rondizio and Siqueira, 1997). Hence the management strategy should be one that will allow the intensive use of the system without depletion of it nutrients via the use of leguminous trees and proper draining systems. If mixed species type of agroforest ry is practiced properly, it can be environmentally sound, ecologically viable, so ciologically acceptable and economically feasible. Mixed species agroforest ry is not a new form of agriculture in Belize C.A. It has been practiced perhaps for centuries by the indigenous people. For example, the Maya have used this form of agricu lture in cultivating their crops while also producing timber and non-timber forest products, including medici nal plants (Levasseur and Olivier, 2000). Agroforestry has also been used in the fo rm of home gardens where several species are grown together (Levasseur and Olivier, 2000; Steinberg, 1998). One of the agroforestry systems receiving much attention presently is the mixed species forest plantations (Jose et al., 2006) Mixed species plantations offer multiple market and non-market commodities or benefits such as food, fodder, timber, carbon sequestration, and soil enri chment among others. Monoculture Systems vs. Mixed Species Systems Monoculture systems have been traditionally used globally to increase productivity. However, pollution due to over fertilization ha s created great interest in finding ways to decrease the amount of fertili zers being used in agricultural systems. Monoculture systems also lead to soil degradation because of over use and extens ive mechanization of farming techniques. Pests have also been a major challenge in monoculture systems which require a vast amount of pesticides that makes the safety of the items produced questionable and also leads to contaminat ion of water resources (Bruntland, 1987).

PAGE 18

8 Furthermore as the cropping system move s from a random mix of plants to a monoculture, the biodiversity of the system decreases. Eventu ally, the productivity of the whole system can decrease (Vandermeer, 1989; Altieri, 1999) because of competition for resources (Jose et al., 2006). Mixed species systems of many species on the other hand are better suited for the environment. The exception to this is the palm trees grown in monoculture systems in the Amazon. Studies have shown that these palm trees grow better in monoculture systems than in mixed species systems (Pollak, Ma ttos, Uhl, 1995). Several studies have indicated that mixed species systems not only produce as much or even more than monoculture systems but they also are better able to prevent soil er osion, leaching of soil nutrients and pollution. Other advantages of mixed species systems are that herbivores are deterred from finding their hosts, nitrogen is utilized more efficiently and it also reduces evaporation (Netting, 1963, 1965; Vande rmeer, 1989; Smith et al., 1997; Stanley and Montagnini, 1999; and Cadisch et al., 2002). Mixed species agroforestry systems may of fer three kinds of benefits to farmers. These are a) increased productivity, b) increased stability and c) increased sustainability. The first benefit regarding total productivity of yield can be higher (i.e. output of valuable products) per unit of land through redu ced damage by pests and diseases. There are several mechanisms that need to be studied in order to understand the advantages of mixed species systems. Thes e mechanisms include advantages of a mixed canopy, deeper rooting system, improvement of soil quality, pest control, resource partitioning and sharing. These mechanisms or factors are briefly discussed in the following sections.

PAGE 19

9 Ecological basis for mixed species systems The ecological foundation for mixed species agroforestry sy stems lies in the structural and functional dive rsity the plantings create at both the site and landscape levels. Mixed species plantings can help a dd structural and functional diversity to landscapes and, if strategically located, they can help restore many ecological functions (Ruark et al., 2003). Mixed species systems are common worldwide. Most agricultural production especially in deve loping countries is done usi ng this type of production (Arnon, 1972; Alas, 1974; Nair, 1990). Since it is so common it has attracted a lot of attention, especially because there are so many systems which are referred to as mixed species or intercropped systems. Vandermeer (1989) lists a total of 55 combinations, but Nair (1990) reported more than 150 systems. According to Lamberts (1980) there are several reasons for cultivating in mixe d species systems, and these include increased productivity or yield advantages; better use of available resources (l and, water, nutrien ts, labour, time); reduction in damage caused by pest s (diseases, insects, weeds); food and cash-flow (economics, human nutrition, greater stability etc.). This aspect of mixed species systems look at the organism and environment interactions in which the organism and the e nvironment affect one another. Hence a plant may influence its neighbour by changing its environment resulting in an effect and response reaction by the individuals involved. The changes need not be negative, but requires a response from the other plants such that a plant may either deplete a resource or may enhance it making it available for its neighbour. However, there are changes that may result in negative effects such as nutrien t extraction that lead s to depletion of a resource or production of shade which may not be good for another individual. A positive

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10 interaction may occur such as the case when trees prevent soil erosion, and deep roots prevent soil nutrient l eaching from the system (Vandermeer, 1989). Mixed canopy According to Gathumbi (2004) a mixed sp ecies system can have a denser canopy than that of a monoculture system when different species occupy different canopy positions and levels, allowing it to capture li ght that would otherwise be inefficiently utilized in monoculture systems (Moral es and Perfecto, 2000; Kelty, 2006). Mixed canopy may also reduce weed competition, by re ducing incident light on the forest floor making the plant unable to photosynthesize and ev entually die. It can also reduce water loss by evaporation directly from the bare soil with the use of cover crops leaving more water for productive transpiration. Furthermor e, evaporation of transpired water or precipitation intercepted by th e canopy may further contribut e to understory temperature reductions (Huxman and Smith, 2001; Unwi n et al., 2006) and the formation of microclimates suitable for other organisms in this way providing habitat for organisms (Ruark et al., 2003). Deeper rooting system A mixed species system may also have a de nser and perhaps deeper rooting system allowing maximum use of soil, thereby increa sing the potential for water and nutrient uptake (because different species may use diffe rent soil depths) (Akinnifesi et al., 1996; Morales and Perfecto, 2000). Coupled with better soil physical properties and the reduction of runoff it may conserve water, l eading to enhanced soil biological activity and nutrient cycling. Through this process it in creases the availability of nutrients which can be readily absorbed by the plant roots at different soil levels since plant roots obtain most of their nutrients from the soil soluti on (Holcomb, White and Tooze, 1982; Smith et

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11 al., 1997 and Cadisch et al., 2002b). Therefore, intercropping or mixed cropping in small plots may have the potential to increase tota l yield compared to those of monoculture plots using the same resource base (Mead and Willey, 1980). This can also result in more efficient use of farm resources, thereby increasing economic returns (Hiebsch and McCollum, 1987). If planned with considera tion for each species' response to mixed conditions, mixed designs can be more produc tive than monoculture systems (Smith, 1986; Binkley et al., 1992; Cannel et al., 1996). Both T. grandis and C. odorata are tall trees 30 to 40 m in height. The T. grandis roots extend to a dept of ~20 feet into the soil column while C. odorata roots have been reported to be superficial with a tendency to become deeply rooted if the soil is loose or coarse. Improving soil quality One of the main conceptual foundations of mixed species system is that trees and other vegetation improve the so il beneath them. Observations of interactions in natural ecosystems and subsequent scientific studies have identified a number of facts that support this concept. Mixed species agroforest ry systems have the ability to contribute significantly to maintaining or improving soil and water quality in a region. However the degree to which these and other ecological functions can be provided will depend on plant species composition and their physic al structure both aboveand below-ground (Wang et al., 1991; Stanley and Montagnini, 1999; Cusack and Montagnini, 2004; Jose et al., 2004). Water relations are very important because water is the medium through which many of the resources are transported. Nitr ogen dissolves in water and moves through mass flow. On the other hand potassium and phosphorous are easily adsorbed on the surface of soil particles and wh en this happens these nutrients move slow in the soil

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12 (Vandermeer, 1989; Brady and Weil, 2002). This means that these nutrients can be immobilized and become unavailable for plan t uptake. However if the soil is fertile allowing organisms to live within it, they can break down those minerals and make them available for plant uptake (Brady and Weil, 2002; Mooney et al., 2002). According to Ruark et al. (2003) three ma in tree-mediated processes have been identified through research which determines the extent and rate of soil improvement in mixed species systems. These are 1) incr eased N input through biological nitrogen fixation by nitrogen-fixing trees 2) enhanced availability of nutrients resulting from production and decomposition of substantial qu antities of tree biomass, and 3) greater uptake and utilization of nutrien ts from deeper layers of so ils by deep-rooted trees (Nair et al., 1999). In addition, a mixture of species, each w ith different nutrient requirements and different nutrient recycling pr operties, may be overall le ss demanding on site nutrients than pure stands because of their niche separa tion (Binkley et al., 1997; Jose et al., 2006). This indicates that the trees are using the nutrients in different proportions and during a different time period in their growth pattern s. In a study of mixed versus monoculture plantations in Costa Rica, M ontangnini et al., (1995) and Montagnini and Porras (1998) found that the growth of domina nt species was faster in mixe d than in pure plantations, and that mixed plantations had high volume and biomass production in comparison with pure stands. In another study, the mixed plantatio ns had intermediate values of soil N, P and K, but lower soil Ca and Mg relative to pure plantations (Sta nley and Montagnini, 1999) which supports the fact that nutrients are used differently throughout a mixed

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13 species system hence there is more nutrient av ailability in a mixed species system than in a monoculture plot. Available light It is common knowledge that the rate of photosynthesis is an increasing function of the intensity of light, so that the rate of photosynthesis increase s rapidly when a low level of light is elevated and increases slow ly when a high level of light is elevated (Vandermeer, 1989; Chapin et al., 2002). T. grandis produces large broad leaves which can be dominant and may decrease the amount a nd quality of light that reaches the plants at the lower level. Another f actor that would affect light penetration is the overlap of canopies leading to reduced light intensity. However in a system where the trees are planted at a distance of 5 m to counteract this effect it w ill not cause a major effect. On the other hand this canopy effect will also be evident after the trees have grown and their canopies have overlapped. In young trees (5 year s) this effect is not evident because the canopy formed still has more space to e xpand without causing negative effects. Furthermore, the physiological a nd morphological traits such as differences in root versus shoot allocation and differences in leaf structure in the trees of the mixed species systems are also playing an important role in the cap ture of sunlight and resources at different levels in the system (Medhurst et al., 2006). The light intensity filtering through a mi xed species system may be sufficient enough for shade tolerant and C3 plants to grow in the understory. Hence it is easier for a mixed species system to utilize available solar energy more efficiently than a monoculture system, especially when caref ul planning is involved (Vandermeer, 1989; Chapin et al., 2002; Unwin et al., 2006). Ho wever, it must remain clear that light

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14 available for photosynthesis diminishes as it moves from the canopy to the lower layers of the system. Mixed species system as a pest management strategy There are many studies on the effect of intercropping on pest attacks. Although studies abound, they are often contradictory due to the difficulty of pointing out the ecological factors that can aff ect insect-plant relations (Kel ty, 2006; Rmert et al., 2002). In one of his studies Andow (1991) analy zed 209 studies involving 287 pest species on mixed species system versus monocultures. When compared with monocultures, the population of pest insects was lower in 52% of the studies (149 species) and higher in 15% (44 species). The population of natura l enemies of the pests was higher in the intercrop in 53% of the st udies and lower in 9%. In another study conducted in the Organiza tion of American States (OAS) funded project site in Belize it was determined that th ere were more pest attacks in the hot pepper monoculture plots than in the mixed species plot (Imhof, 2004). The results of such studies therefore imply a complex situati on in which the specific agro-ecological situation is important. However, in order to develop mixed species cropping as a tool it is necessary to understand the underl ying mechanisms involved. Plants belonging to the same or a very cl ose taxonomic group have the tendency to share common pests. In agroforestry system s, aligophagous and polyphagous insect pests are expected to thrive if both components belong to the same or a closely allied taxonomic group. An insect feeding on a plant with a certain biochemical make-up will adapt more easily to closely related plants wi th similar biochemical constituents than to species that have entirely different constituents because of taxonomic differences. A mixed species agroforestry system comprise d of plant species belonging to different

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15 taxonomic groups is expected to be less affect ed by insect pests than a system composed of closely related species as in a monoculture system (Vandermeer, 1989). Under natural conditions, even insects with a limited host range have been observed to feed on taxonomically diverse spec ies of plants. In a mixed species system, therefore, the plants assembly should consis t of species that do not double as host for insect pests of other plants in the system whether crops or woody perennials. Some insects utilize different host plants as food in their larval stages fr om those eaten in the adult stage. So an even greater range of plants in a mixed species system may be attacked by different stages of an insect pest. If all or most plants in a mixed system ar e palatable to a polypha gous pest, then it is likely that the insect will stay longer and become more numerous, causing greater damage. Therefore, monophagous pests can be controlled altogether by not including their host plants in the system. The host range of oligophagous pests can also be narrowed by eliminating palatable species form the assemblage and replacing them with non-host plants. Therefore whats important to remember is that farmers need to be knowledgeable about such pest relationships in order for them to be able to make informed choices when preparing their fields. There are two existing hypothesis proposed initially by Aiyer (1949) and redefined later by Root (1973) and proposed as three hypothesis by Vandermeer (1989) in reference to the presence of pest in an area; (1) the di sruptive crop hypothesis in which a second species disrupts the ability of a pest to efficiently attack its proper host (specialist herbivore) (2) the trap crop hypothesis in which a second species attracts a pest that would normally be detrimental to the princi ple species (generalis t herbivore) (Hokkanen,

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16 1991) and 3) the enemies hypothesis in which natural enemies are more effective and numerous in diverse systems reducing th e pests through predation or parasitism. Therefore it can be said that the first hypot hesis more closely expl ains observed pest attack on the study conducted in the trees funded by the OAS in Belize although the exact mechanism of concentration on the resource is not defined. Ho wever, there are currently several competing explanations which ar e probably best summarized by Finch and Collier (2000). These authors speculate that insect pests settle on plants only when various host plant factors such as visual stimuli, taste and smell are satisfied. This is more likely to occur in monocultures than in mixed species systems where the chance of encountering a wrong stimulus is much in creased. Therefore, the complexity of the overall picture makes it difficult to specifically design intercrops for pest control without practical knowledge of pest and crop bi ology which sometimes can be obtained through research and traditional ecological knowledge (Hokkanen, 1991). There is a list of pests and diseases which a mixed species system is said to control. These include a reduction in in sect attacks, nematodes, di seases, herbivore attacks, aphids, and weed control (Risch et al., 1983; Leibman, 1986; Andow, 1991) among others in which a specialist pe st is said to be deterred fr om its host through the disruptive effect of a mixed species syst em of plant (Trenbath, 1976). Current Project The objective of the study was to examin e growth and soil fertility status of monoculture and mixed species plantations of Cedrela odorata L and Tectona grandis L in Belize. We hypothesized that mixed species plantations will have higher soil fertility and better growth compared to monoculture plantations because of the synergistic

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17 interactions when species are mixed together The following chapter describes the study in detail.

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18 CHAPTER 2 GROWTH RATE OF TECTONA GRANDIS AND CEDRELA ODORATA IN MONOCULTURE VERSUS MIXED SPE CIES PLANTATIONS IN BELIZE Introduction The forests of Belize cover slightly more than 85% of its surface area which is very different when compared to neighboring countr ies in Central America that have not been as successful as Belize in protecting their fo rests. According to the FAO the rate of deforestation in Belize is rela tively low (i.e., approximately 0.25% per year compared to other countries in the region) (FAO, 1997). The va st majority of these forests, situated in central and southern Belize, are tropical rainforests which constitute an important reservoir of biodiversity worldwide. Furtherm ore, they are an important source of wood, medicinal plants, and all kinds of natu ral products (Bruntland, 1989; Boot, 1997). Although Belize has been able to preserve mo st of its environmental resources to a much greater extent than other Central Am erican and Caribbean countries, its economy has been and will remain highly dependent on environmentally-based industries (FAO, 2001). The forests of Belize are by no mean s undisturbed; they are dynamic and range from freshly burned milpas to dense tropical forests. The main cause of forest degradation in Belize is slash-and-bu rn agriculture (with no fallow period), as practiced by the Maya and the Mestizo population (Arya and Pulver, 1993). Slash and burn agriculture in Belize l eads to permanent agriculture; in which crops are rotated initially, but become permanent at a later stage. It is in this system that the mixed species is mostly centered on, becau se trees are planted for several purposes including food, fodder, timber and medi cinal purposes among other uses.

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19 Problem Statment Belize has a low population density of hardwood trees species such as Swietenia macrophylla King and C edrela odorata L, growing naturally in the forests (Levasseur and Olivier, 2000). In spite of this situati on there is an increa sing demand for hardwood lumber locally. This demand is further inte nsified by the rise of new industries like tourism, which is currently the main income generating industry in Belize (World Fact Book, 2007). Among the various forms of tourism, ecotourism seems to demand the most natural resources includ ing timber. Those operations build st ructures that are aesthetically appealing to foreign travelers, often requiring the use of local construction material. This form of tourism is placing an even greater demand on lumber for the construction of resorts instead of alternative buildin g materials (Primack et al., 1997). In 2001 and 2002 Belize experienced a catastr ophic infestation of the Southern Pine Bark Beetle, which totally destroye d the countrys largest managed forest ecosystem, Mountain Pine Ridge Forest Rese rve. This forest was 31-years-old, and consisted of the Caribbean White Pine ( Pinus caribaea ) species which was selectively harvested for timber (GOB, 1996). The plantation is now unproductive and in a regeneration phase. The demand for hardw ood remains which has forced the logging industry to revert to harvesti ng of timber in natural fore st stands. This option makes forest reserves and other unprot ected forests vulnerable. With forest reserves not well monitored (because of lack of personnel) by the Forestry Department of the Government of Belize (GOB), many designated forest reserves are being illegally harvested. C. odorata and S. macrophylla are the two hardwood species targeted. These species are harvested uncontrollably in various sizes, in some cases, before the trees are at the regulated DBH size or mature enough to repr oduce. Other hardwood trees species are

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20 also been extracted for domes tic and export uses. However, C. odorata is the preferred hardwood species domestically and has beco me scarce (GOB, 1996; Primack et al., 1997). As logging becomes unproductive, there is a shift towards agriculture, which leads to increased negative impacts such as defo restation and soil degradation. This keeps exerting pressure on forest managers and scie ntists to seek alternative ways to meet demands for timber. The demand for timber is projected to increase consistently. One promising alternative to incr ease timber production is agrofore stry in the form of mixed species systems. Mixed Species Systems in Belize Traditionally C. odorata ( Cedar ) and leguminous trees (i.e. Lonchocarpus castilloi ( Black cabbage bark ) and Sweetia panamensis ( Billy Webb ) ) grow naturally in the subtropical forests of Belize. A more re cent timber species of choice is Tectona grandis ( Teak ). These tree species are now being incorpor ated into agricultural farming systems, for purposes other than timber production such as protection against soil erosion, nutrient cycling, and shade. Similarly, cash crops va rieties such as hot peppers and papayas are intercropped in these systems. However, wh en these trees are grown in managed mixed species agroforestry systems (Nair, 1984), especially in plots that includes other leguminous plant species such as Lonchocarpus castilloi ( Black cabbage bark ) and Sweetia panamensis ( Billy Webb ) and ground cover crops such as the perennial Arachis pintoi (pinto peanut), competition for essential nutrients and sunlight may be less severe than in monocultures because of the niche separation (Vandermeer, 1989; Jose et al., 2006).

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21 Mixed species systems are commonly used in Belize in subsistence farming. However, there is a common perception that these systems are more time consuming to care for and demands higher invest ment at the initial plantati on phase. Furthermore, it is perceived that mixed species systems are not as productive as monoculture systems, and that the trees do not trive as well as in monoculture. It woul d seem to farmers that the results are not the same as those obtained in a monoculture plantation. Hence, few hardwood trees have been intercropped in these systems. The ecological aspect of a mixed species system is seldom taken into consideration when establishing hardwood tree plantations. Ho wever, several studies have shown that mixed-species plantations have a high poten tial for accelerating the process of natural succession and establishing a stand of ecol ogically and economically desirable trees (Montagnini, 1999; Dommergues and Rao, 2000). Other studies have also shown that mixed-tree plantations could be an effective tool for allevia ting site degradation, acting as a catalyst for forest regeneration and rehabilitation (Lugo, 1988; Parrotta, 1995). The idea behind a mixed species systems is to capitalize on the beneficial interactions between the speci es planted while avoiding nega tive interactions. Results from studies done in Belize show that mo re favorable credit rates, labor saving technology, and intensive shade management ha ve the strongest potential to increase smallholder income (Levasseur and Olivie r, 2000). If mixed sp ecies systems were continuously implemented adding annual shade tr ee crops such as fruits, nuts, or spices there is potential to significantly improve sm allholder income. Furthermore, since the systems are usually small plots (~5ha), labor is mostly carried out by family members;

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22 thereby reducing the monetary input into es tablishing and managing these mixed species systems. In order for mixed species production systems to become an important land use practice in Belize, the farmers have to be convi nced about the benefits of these systems. Scientific evidence is now available to show that the spatial and temporal heterogeneity created by the mixed species plantings can help enhance resour ce availability and capture, increase production, reduce risk of inte nsive agricultural and forestry practices, and achieve system stability and sustainabi lity (Lefroy et al., 1999; Nair, 2001). Mixed species plantations also yield more divers e forest products than monoculture stands, helping to diminish farmers risks in uns table markets. Lastly mixed species cropping could also be an important tool for pest and disease management in agriculture or farming systems as has been shown by studies done by Morales and Perfecto (2000) in Guatemala; Montagnini et al (1995) in Costa Rica; and by Kelty (2006) and Risch et al. (1983) who reviewed published articles on mi xed species systems and pest management. Unfortunately, there is no documentati on on the performance of mixed versus monoculture systems for popular species in Belize. Therefore it is not likely to be widely adopted by commercial farmers until the potentia l benefits have been fully evaluated and can be shown to outweigh those of the monoculture systems. Study System This study examined the growth and so il chemical properties of mixed and monoculture plantations of C. odorata and T. grandis in Belize. We hypothesized that C. odorata and T. grandis trees growing in mixed species treatment will produce more volume than in monoculture treatment; survival and growth of selected tree speci es will be better in mixed-species than in monoculture treatment;

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23 growing C. odorata and T. grandis in mixed species plots will improve soil quality by increasing soil organic ma tter and nutrient content. Characteristics of Cedrela odorata and Tectona grandis The species used in the current study are different in their physiology and perhaps can compliment each other in the use of resources. C. odorata has monopodial growth, with orthotropic branches th at form an open crown. It has large, pinnately compound leaves that can be up to a meter long, with 10 pairs of leaflets, each about 40 cm2 (Hiremath et al., 2002). On the other hand, T. grandis has an umbrella like crown with large, thick leaves whose leaves are simple and opposite, hence it allows the infiltration of sufficient light for photosynthesis by the understory plants. The rooting pattern of the trees is also of interest since it determines the extent to which these trees are tapping the soil nutrients. T. grandis root extend to a dept of ~20 feet into the soil column while C. odorata roots are mostly superficial but becomes deeply rooted if the soil is loose or coarse. Materials and Methods Study Area The study was carried out in the Cayo Distri ct (Figure 2-1) in Belize (16' and 17' north latitude, and 88' and 89' west longitude). The soil varies in texture from sandy loam to sandy clay but invariably cont ains angular quartz grit. It is acidic and has very low contents of available plant nut rients (King, Baillie, Abell, Dunsmore, Gray, Pratt, Versey, Wright, Zisman 1992) except for calcium. The area experiences a mean annual rainfall of 1400 mm with a mean temp erature of 26C (Figure 2-2) (Hydromet Services, 2006).

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24 Mean rainfall in this area during the study period ranged fr om 75 mm to 286 mm per month between May through August with th e wettest month being in August and the driest month in July 2005. Rainfall pattern differed in 2006 during which there was more rainfall during the months of June and July declining in August (Figure 2-2). This research was carried out in conjunc tion with an ongoing agro forestry research project funded by the Organization of American States. Hardwood trees species grown in the western parts of Belize in the Cayo Distri ct provide an excelle nt case study for the potential of hardwood tree species system s to address the needs of limited timber resources in Mesoamerica and the Caribbean. Experimental Design and Measurements The experiment was set up as a comple tely randomized design with five replications. Each plot was 471.5 m2 and contained 40 trees. The two treatments were monoculture ( C. odorata or T. grandis alone; i.e. 40 trees of th e same species per plot) and mixed species plantation ( C. odorata and T. grandis mixed together in the same plot for a total of 40 trees per plot; i.e. 20 trees of each species). The mixed species plot also had ground cover of A rachis pintoi Swietenia macrophylla and the leguminous trees, Lonchocarpus castilloi, and Sweetia panamensis. However only C. odorata and T. grandis were used in this research. The crops that have been traditionally intercropped in the mixed species plots have been hot peppers ( Capsicum chinense Jacq) and papayas ( Carica papaya ). The hardwood trees studied were pr uned after the first three years. Each hardwood tree and leguminous trees were systematically planted at a distance of 5 m from each other (the papaya and hot peppers were intercropped in the space between the trees) The trial did not receive any ir rigation, fertilizers an d pest control.

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25 Height and ground line diameter (GLD) we re measured on a weekly basis from May through August in 2005 and in August 2006. Tree height was determined using a height pole, while diameter was measured with a digital caliper. Stem volume index (SVI) was then calculated using the following formula: SVI=GLD2 x height. Volume yield of monoculture and mixed species plantations was compared using the Land Equivalent Ratio (LER) using the following formula: LER = SVI C. odorata (mix) / SVI C. odorata (monoculture) + SVI T. grandis (mix) / SVI T. grandis (monoculture). The LER is the ratio of the area needed unde r monoculture to a un it area of intercropping at the same management level to give an equal amount of yield. Therefore it compares the performance in intercrop to the performan ce in monoculture of a particular species; i.e., in this case T.grandis and C.odorata in mixed versus monoculture systems. Soil samples (0-15 cm) were collected from the mixed-species and the monoculture plots twice (2005 and 2006), but data were pooled since no differences were found between years. Soil samples from the mixed species plot appear as one soil because the soil was taken from the plot consisting of bot h trees. Soil samples were processed by air drying overnight, removing root parts and large stones, and crushing remaining soil until finely ground. Samples were analyzed for organic matter, pH, CEC, K, Ca and Mg content. Ca, K, and Mg were extracted using neutral normal ammonium acetate, and analyzed by atomic absorption spectrophotomet er. Soil pH was measured in a 2:1 soil: water slurry made with deionized wa ter. Organic matter was analyzed by dichromate/colorimetric method while Cation Exchange Capacity was calculated from

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26 the cation results. All analys es were performed at a comm ercial lab (A & L Southern Agricultural Laboratories, Inc., Pompano, Florida). Leaf samples were also collected during the first year for foliar chemical analyses. The foliar tissue samples were first washed and oven dried (75C) for 48 hr. The dried tissue samples were ground in a Wiley Mill. Foliar samples were digested by a wet ashing procedure using sulfuric acid and hydroge n peroxide. The digest is then filtered and fractioned. The different elements were analyzed using atomic absorption and UVVisual Spectroscopy (Wolf, 1982). All analys es were performed at a commercial lab (A & L Southern Agricultural Laborat ories, Inc., Pompano, Florida). Statistical Analysis Data was analyzed using ANOVA within th e framework of a randomized complete design using SAS. The dependent variables were tested for normality using the Shapiro Wilk statistic. Duncans test was used for mean separation if ANOVA revealed significant differences at =0.05. Results And Discussion Survival Rate of T. grandis and C. odorata Survival of trees varied between treatment s. Five years after planting, there was a survival rate of 77 % in monocu lture treatment. On the other hand, the survival rate of the mixed species treatment was a little higher at 80%, considering that most mortality occurred on the C. odorata trees due to the Hypsipyla grandella Zeller infestation. Individually, the survival of C. odorata in the mixed species treatment was 75% while that of the monoculture treatment was 77.5%. The survival of T. grandis in the mixed species treatment was 85% while on the m onoculture treatment it was 77.5%. The

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27 overall results indicate that th e survival rate of trees in the mixed species treatment was better than those in the m onoculture treatment. Growth T. grandis grown in mixed species system had greater growth increment (Figure 2-3) compared to monoculture during 2005 and 2006 (Figure 2-4). Similar growth pattern was recorded for GLD a nd SVI. Height and GLD of T. grandis at the end of the growing season in 2006 showed significan t differences (p<0.0001) between the monoculture and mixed species systems. T. grandis trees in the mixed species plots were 40% taller than those in the monoculture plots. Again, similar patter ns were observed for both GLD and SVI. For example, SVI of T. grandis in mixed species system was 0.91 m3 per ha. compared to 0.49 m3 per ha in monoculture (Table 2-1). Height increment of C. odorata was significantly different between the monoculture and mixed species systems as de picted by the different letter in Figure 2-3 and 2-4. The growth rate of the C. odorata trees was better than that experienced by the trees in the mixed species system. Height increment in the mixed species system was impacted mostly by a shoot borer, H. grandella, which attacked the leading shoots (Cornelius and Watt, 2002), which had to be pruned regularly. GLD, however, was greater in the mixed species system compared to monoculture. It was noted that the most growth occurred during the beginning of th e growing season (wet/rainy season). The growth pattern observed was similar to wh at Worbes (1999) found in Venezuela in a study done on T. grandis and C. odorata among other tropical trees and by Dunisch et al. (2002a) and Dunisch et al., ( 2003) in studies done in Ce ntral Amazon on the growth increment of C. odorata.

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28 Stem volume index (SVI) per ha was also computed and compared (Table 2-1). The comparison of SVI revealed significant difference between T. grandis in mixed versus monoculture plots (p<0.0001), but there was no difference between C. odorata in mixed vs. monoculture plots (p <0.001). The growth rate re corded during this study was similar to those obtained in other studies for T. grandis and C. odorata despite the H. grandella attacks in these plots (Montagnini et al., 1999; Parrota, 1999). The LER for the mixed species system was 1.47, which indicates that there is some sort of facilitation occurring because of a modi fication of some environmental factor(s) in a positive way by one or both of the species being intercropped. The mixed species system could be beneficial compared to monoc ulture plantations of the same species. It appears that intercropping does not affect the growth rate of C. odorata trees although the height of the trees in the mixed speci es plot was severely affected by the H. grandella attack. However, T. grandis growth was significantly im proved as a result of mixing species. So, overall, mixed species syst em had higher production potential than monoculture. This is similar to the findings of other researchers in which they found that mixed plantations had overall greater growth in the mixed species systems compared to the monoculture ones (Montagnini et al ., 1993, 1995; Montagnini and Porras, 1998) which can be a result of the leguminous tr ees intercropped with in the system. According to Vandermeer (1989) if an expe rimental plot yields an LER greater than 1.0 it is certainly true th at facilitation has been demons trated in the system. Hence competition may be minimal, because competition cannot be eliminated totally from such a system since resources are certainly being us ed, but possibly from di fferent levels of the soil column and at different ti mes of their growing period.

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29 Vandermeer (1989) suggests that the LER measurement takes its name from its interpretation as relative land requiremen ts for mixed species versus monocultures. Therefore, what we are looki ng at is whether the monocu lture plots are producing the same amount of biomass as the mixed species sy stems or vice versa. If the LER is greater than 1.0 then the mixed species system is mo re efficient. If it is less than 1.0 then monocultures are more efficient system s of production of the hardwood trees. Foliar Nutrients According to Goncalves et al. (1997), Mont agnini and Sancho (1994), Folster and Khanna (1997), soil nutrients may be generally abundant early in sta nd growth as a result of low plant uptake, stimulat ion of nutrient mineralizati on, and low immobilization in plant biomass, but as plantations grow, decr eased nutrient availability can result from immobilization into woody biomass and detr itus pools, and decreased mineralization (Binkley et al., 1997; Folster and Kh anna 1997; Wadsworth 1997). Therefore, alternatives to conserve site nutrients ma y include preferential planting of tree species that do not place high nutrient demands on the site (Bruijnzeel, 1984; Wang et al., 1991; Montagnini and Sancho, 1994). Information avai lable is usually on th e effect of trees on monoculture systems while the effect of different trees on mixed species system is minimal. Table 2-2 shows the range in concentration in the leaf for the elements N, P, K, Ca and Mg observed during the research. However, there is insufficient data to evaluate the treatment differences in leaf co mposition for these elements in T. grandis and C. odorata Although limited samples prevented a statistical comparison, it appears that there is more calcium, magnesium and nitrogen in the leaves of the C. odorata in the mixed species plots than those of the monocu lture plots (Table 2-2). The higher nitrogen may be due to

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30 the presence of nitrogen fixi ng trees and the nitrogen fi xing cover crop in the mixed species plots. However, there was more phosphorous and potassium in the leaves of the C. odorata in the monoculuture plot than in those of the trees in the mixed system plot. The result for leaves of the T. grandis shows that there is again more nitrogen along with more potassium in the mixed species plot co mpared to the monoculture plot. The nutrient level of phosphorous, calcium and magnesium are the same for trees in monoculture versus those in the mixed species system. The mixed species plot has a diverse amount of trees and other crops (hot peppers and papaya) intercropped annually which woul d mean that more nutrients are being utilized in the mixed species plot. However, th e results of the foliar analysis indicate that although there is extraction of the resources through harvest of the crops the mixed species plot still has overall more available nutrient resources in the mixed species plot compared to the monoculture plot. Soil Fertility Contrary to our expectat ion, there was no significant difference in soil organic matter, pH and K between soils of the monoculture C. odorata and the mixed species treatment However, there was difference noted in Mg which was higher in the C. odorata monoculture plot compared to mixed species plot (Table 2-3). Marked difference in soil CEC between the mixed and the monoculture systems was also observed with mixed species systems exhibi ting higher CEC than monoculture system. The fact that soils under mixed species had higher CEC perhaps points to the higher soil fertility in the system. The soil under monoculture T. grandis had lower CEC, and lower organic matter compared to the mixed species plot. However, the other nutrients (pH, K, Mg and Ca)

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31 were not different between the two treatments. The higher growth observed in T. grandis could be a result of the higher CEC in th e mixed species plot (Table 2-3). Higher soil fertility in mixed species sy stems compared to monocultural systems has been reported in other studies done in Puerto Rico by Parrotta (1999), and also in Costa Rica by Montagnini (2000). They found that soil fertility was higher in mixedspecies plantations of Strephnodendron microstachyum Vochysia guatemalensis Jacaranda copaia and Callophylum brasiliense than in pure stands of C. brasiliense and V. guatemalensis Stanley and Montagnini (1999) obtai ned similar results in a study on nutrient accumulation in pure and mixed planta tions in Costa Rica. This implies that there is perhaps faster nutrie nt cycling and turnover in mi xed species systems than in monocultures, making the soil fert ility higher in the former. It is also possible that the mixed species system has a better nutrient us e efficiency. As suggested by Jose et al. (2006) and Binkley et al. (1997) in a mixture of species, each with different nutrient requirements and different nutrient recycli ng properties, there may be overall less demand for on site nutrients because of the ni che separation. This means that each plant utilizes the resources at a diffe rent stage in their life cycle or at different rates. On a study done by Stanley and Montagnini ( 1999) in plantations of mixed versus monoculture, the mixed plantations had intermediate values of soil N, P and K, but lower soil Ca and Mg relative to pure plantations wh ich was similar to those obtained in this experiment. It is possible that Ca and Mg are removed from the soil and stored in the plant biomass during the active growing seas on, and are subsequently removed when the plants are harvested.

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32 Conclusion The results obtained during this research have led to the conclusion that when C. odorata and T. grandis are grown in mixed species syst ems with leguminous trees they have the capacity to produce a higher yi eld compared to monoculture treatment. Although we did not measure litterfall which sh ould have given an indication of exactly how much litterfall occurred in both system s it was evident that there was efficient cycling of nutrients in the mixed species system because of the higher soil C.E.C in the mixed species system compared to the monoculture plot. Similar results have been obtained by several researchers who have invest igated similar treatments in the tropics (Binkley et al., 2003; Montagnini, 2000; Stanley and M ontagnini, 1999; Parrotta, 1999) in which they found that mixed species systems produce a more complex array of litterfall releasing nutrients b ack to the soil at different ra tes because of the composition of the leaves. Therefore, mixed-species plan tations have the potential for out-producing monocultures, but actual yields depend on soils silviculture, and species. It is important to know more about these inte ractions to provide a solid foundation for mixed-species management of plantations (Binkley et al., 2003; Dommergues and Subba Rao, 2000). It was expected that the presence of L. castilloi and S. panamensis, both N2-fixing trees and the cover crop A. pintoi, would result in hi gher productivity of T. grandis and C. odorata because of their ability to fix nitroge n and make it available for the trees. However, these expected effects could not be ascertained because of the limited foliar and soil analysis data. However there was a te ndency of higher yields per plant in the T. grandis and C. odorata associated with L. castilloi and S. panamensis than in the monoculture system, possibly due to an i ndirect effect of n itrogen fixation by the leguminous trees. Based on the growth reco rded throughout the study period it can be

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33 surmised that the two species are coexisting probably because their niches do not overlap sufficiently for them to become competitive. This research did not investigate the soci ological component but it is imperative that we recognize that an agro forestry system cannot operate without farmers. Farmers are a rural population; they produce for themselves but also produce for the markets. Their economy depends on family labor but they often employ themselves and employ others as needed. Therefore, as rural producer s they are an important social category of contemporary societies and need to be recogn ized especially by the political authorities who control the economic and developmen t policies in rural area (Nettings, 1993).

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34 Figure 2-1. Map of Belize showing project/research si te in the Cayo District.

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35 0 50 100 150 200 250 300 350 mayjunejulyaugust monthtemperature (C) rainfall (mm) Rainfall 05 temperature 05 Rainfall 06 temperature 06 Figure 2-2. Graphical description of the monthly weather patterns (temperature (Co) and rainfall (mm)) of the study region in Belize during the study period May August 2005 and 2006. Rainfall varied throughout the study period but temperature remained constant.

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36 0 0.2 0.4 0.6 0.8 1 1.2 1.4 C.odorataT.grandisSVI (cm3) 0 0.5 1 1.5 2 2.5 3GLD (cm) mono mixed 0 0.5 1 1.5 2height (m)a a a a a a a b b b b b Figure 2-3. The growth increment per month (measured during a 3 months active growing season in 2005) of C. odorata and T. grandis in mixed species and monoculture plots at the study site in the Cayo District, Belize. For each variable, differences among treatments are statistically significant when followed by different letter.

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37 0 0.2 0.4 0.6 0.8 1 1.2 1.4 C.odorataT.grandisSVI (cm3) 0 0.5 1 1.5 2 2.5 3GLD (cm) mono mixed 0 0.5 1 1.5 2height (m)a a a a a a a b b b b b Figure 2-4. Final height (m ), GLD (cm) and SVI (cm3) of C. odorata and T. grandis at four years after planting in mixed species sy stems versus monoculture systems at the study site in Cayo District, Beli ze. The difference among treatments are statistically significant when followed by different letter. Error bars represent S.E of the mean.

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38 Table 2-1. Stem volume index of T. grandis and C. odorata in mixed species system compared to those in monoculture syst ems, four years af ter planting in the Cayo District, Belize. Differences among treatments are statistically significant when followed by a different letter using Duncans test to note statistical difference (p<0.05). SVI (m3/ha) Treatments T. grandis C. odorata Monoculture system 0.4999257 a 0.146872 a Mixed species system 0.9100141 b 0.1656123 a

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39 Table 2-2. Foliar analysis results per treatmen t. Chemical characteristics of the leaves from C. odorata and T. grandis at age four in mixed and monoculture systems in the study site in the Cayo District, Belize. Leaf parameters Monoculture C. odorata T. grandis Mixed C. odorata T. grandis Nitrogen (% ) 4.5 3.8 4.7 3.9 Phosphorous (%) 0.31 0.19 0.16 0.14 Potassium (%) 3.58 2.47 2.59 2.50 Magnesium (%) 0.16 0.23 0.17 0.13 Calcium (% ) 1.80 1.40 1.90 1.40

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40 Table 2-3. Chemical characteristics of the top soil to 15 cm depth for monoculture and mixed species systems, Cayo District, Belize. S.E is shown in parenthesis. For each variable, differences among trea tments are statistically significant when followed by different letter using Duncans test to note statistical difference (n=9, p<0.05). Soil parameters Monoculture C.odorata T grandis Mixed C.odorata T.grandis Soil pH (%) 6.5(.1) a 6.9(.45)a 7(.2) aa Organic matter (%) 7.0(.45) a 5.5(.55) a 6.4(.95) ab C.E.C (meq/100g) 31.9(3.4) a 40.9(5.3) a 46.4(7) bb Exchangeable K (%) 0.55(.05) a 1.1(.1) a .9(.35) aa Exchangeable Mg (%) 11.75(.85) a 10.3(.45) a 9.7(1.9) ba Exchangeable Ca (%) 81.8(2.65) a 86.0(2.85) a 88.6(2.45) ba

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41 CHAPTER 3 CONCLUSIONS AND RECOMMENDATIONS It is well known that a mixed species plan tation have many advantages for farmers, among them being that the farmers can grow short-term cash crops and obtain some annual income while they wa it for the long-term benefit from wood production from the associated trees. However, in the case where C. odorata is being used we must reiterate that the C. odorata is highly susceptible to th e attack of the shoot borer H. grandella Zeller, which is considered to be one of the most severe fore st pests in Latin America and the Caribbean (Hilje and Cornelius, 2001). On the research site, the C. odorata grown in the mixed species system is constantly being attacked by the larvae which results in many branches which makes the tree unsuitable for commercial timber production. The use of intercropping can be a viable al ternative for many farmers. Therefore, it is very important and necessary that information about the fa ctors that affect or enhance C. odorata and T. grandis growth is made available to thos e interested in this system of production. The current study attempted to do so by investigating the growth rate of C. odorata and T. grandis in mixed and monoculture system to determine which system produced the highest yield. Mixed species systems are very importan t systems that if planned properly can provide many benefits for the farmers. Based on this research it can be concluded that in terms of growth rate in height and diameter of C. odorata and T. grandis mixed species systems are better than monocultures. In mi xed species systems, the layers that are formed by the tree canopies provide a microclimate of their own.

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42 In the mixed species system under investigation the C. odorata trees suffered a lot of damage from the H. grandella larvae attack. This was as a result of intercropping S. macrophylla and C. odorata in the same plot at the same time since both trees are host for the H. grandella Furthermore, this plot is at the edge of a natural forest where other mature C. odorata and S. macrophylla trees are growing. Theref ore, there is a potential source of food which keeps the larvae present throughout the year in this treatment. On the other hand the monoculture treatment is located about 200 meters away from the mixed species treatment and the land around it has been cleared. Therefore, there are no mature C. odorata trees in their vicinity. Furthermor e, this plot was established leeward from the mixed species plots. So what are the implications for farmers today? There are se veral positive findings that will aid farmers in their decision to continue or to st art farming using mixed species systems. Montagnini (1994), Montagnini et al. (1995), Parrota (1999) and Jose et al., (2006) have shown that mixed species systems are not only good for the environment, but can be economically better than monocultures. Farmers need to contact the experts at th e Agriculture and Forestry department in their home country and also the leading experts in research such as the Universities or other local NGOs who can provide support and advice in the planning and preparation of their fields. According to Vandermeer (1989) the basic structure of a plantation imposes certain inevitable microhabitat f eatures at level of the ground. It is through an analysis of these necessary features that we can gain an idea of how the system should be designed to eliminate competition between species which might require the same resource at the same time for their growth. On the other hand pl ants or crops which are host to polyphagous

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43 pest should also be avoided to eliminate or decr ease pests, or insect attack to the crops or trees. When planning their overstory crop the farm er must take into consideration the shade effect to the lower level plants. He nce, canopy structure should be considered so that the system does not produce too much shade for the understory crops. Hence if hardwood trees are being used they should be trees with different canopy structures. For example C. odorata produces a canopy with orthotr opic branches that form an open crown, while S. macrophylla produces a closed canopy and T. grandis produces a canopy that forms an umbrella-like crown allowing th e infiltration of sunlight to the understory plants. A plantation using similar trees woul d allow enough sunlight to penetrate through the layers for photosynthesis to occur on the plants at the lower level. Once the effect of the overstory species is known each speci es in the understory should then be characterized with respect to the daily light environment needed for their survival. Every mixed species system should have a ground cover crop which provides the first resource for the farmer. Many leguminous crops such as beans, peanuts, peas etc. can be used as ground cover crops. These plan ts will provide food for the family and will also aid in the recycling of nitrogen making it available for plant. A ground cover crop also protects the soil from erosion and main tains a suitable microhabitat for organisms in the soil and the same time acting as a filter re ducing the time it takes for the residues of dangerous chemicals to enter the ground water reservoirs thereby allowing the breakdown by bacteria of these harmful chemi cal residues. Of much importance also is the fact the a ground cover crop wi ll reduce or act as a weed control, thereby reducing the

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44 amount of labor that would be needed in a system with no ground cover crop (Vandermeer, 1989). Results from this research indicate that mixed species can provide higher yield. Many studies done in tropical countries such as Mexico (Primack et al., 1997), Puerto Rico (Parrota, 1999) and Costa Rica (Montag nini, 1999) and now Belize have indicated that better growth rate is obt ained from trees growing in mixed species systems compared to monoculture systems. Intercropping of T. grandis and C. odorata with the leguminous trees and cover crop has shown an increase of volume production in both hardwood trees in the mixed species systems when compar ed to those of the monoculture systems producing an LER of 1.47. This result could le ad to important changes in cultivation practices mainly for growers wishing to produce timber with minimal insecticide and fertilizer input. When nitrogen fixers used as ground cover are in tercropped with other crops they can help protect the crop from insect pests, enhance the ra te of organic matter, reduce erosion, supply extra nitrogen to th e system and decrease the germination and development of weeds (Coolman and Hoyt, 1993; Ramert, 1995). There is also a variety of l eaf litter or organic matter produced from these systems, since plants intercropped are different and they may shed leaves that decompose at different rate thereby making nutrients availa ble during different inte rvals. This also means that these soils are hosts to a variet y of organisms which are beneficial to the system as nutrient recyclers. A very important factor is that you minimize the amount of fertilizers needed to produce your crops. Leguminous trees should also be intercropped as much as possible to maintain a consta nt flow of nitrogen through the system.

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45 Mixed species systems have been investig ated as a strategy for pest control. Although the results are inconclu sive in our trial, based on the literature it can be said with some certainty that mixed species syst ems do reduce pests in most instances. More research is needed to point to the exact proc ess involved in this st rategy. Several studies have shown a decrease in pests when cr ops are intercropped when compared to monocultures. The most outstanding element in this is the fact that the farmer minimizes risks when using mixed species systems. Mulch can be produced from leguminous tree s within a mixed species treatment. This mulch which is sometimes referred to as green manure or green fertilizer can be placed strategically at the base of the plants that are bei ng cultivated and allowed to decompose to be recycled back into the system. The decomposition of the mulch would release the nutrients within the mulch and make it available for plant uptake. Hence, natural fertilizer is added to the system wit hout the fear of pollution. Therefore, this not only is economically better, but ecologically viable and sociologically sound since the soils and waterways remain clean. Furthermor e, the produce is also free of synthetic fertilizers and chemicals. More organic matter means healthier soils and healthier soils means better yield. The recycling of organic matter occurs in a cycle. Leaves are shed from the trees or crops and are broken down by the organism in the soil. These organisms then recycle the nutrients within the soil through excretions and also when they die and decompose. These nutrients are then taken up by the plants which use them and return them to the soil as litter fall. The organisms then go th rough the same process making the nutrients available for plant uptake. Therefore, it must be stressed that a fertile soil is very

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46 important for plant production and also for the survival of organisms which are the recyclers of nutrients. In summary, mixed species systems have many advantages for farmers and can be practiced as an alternative land use strategy.

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47 LIST OF REFERENCES Aiyer, A.K.Y.N., 1949. Mixed cropping in Indi a. Indian J. Agri. Sci. 19:439-543. In Vandermeers (1989). The Ecology of Interc ropping. Cambridge University Press. Cambridge. Alas, L.N., 1974. Breve descripcion del sist ema de produccion del pequeno productor en El Salvador. Apendice F. In Conferenci a sobre systemas de produccion agricola para el tropico. Cent. Agron. Trop. De Inve st. y Ensenanza. Informe final. CATIE. Turrialba. Costa Rica. Altieri M.A., 1999. The ecological role of biodiversity in agroecosystems. Agriculture Ecosystems and Environment 74, 19-31. Altieri M.A. and Hecht, S.B., 1990. Agroeco logical and Small Farm Development. Boston: CRC Press. Andow DA., 1991. Vegetational diversity and arthropod population response. Annual Review of Entomology 36, 561-568. Arnon, I., 1972. Crop production in dry regions. Leonard Hill, London. Arya L and Pulver E.L., 1993. On-site appraisal of target areas for su stainable agriculture production activities. Natural Resource Management Protection Project (NARMAP), Belmopan, Belize. Atkinnifesi, F.K., Kang, B.T., and Fajani -Eniola, H., 1996. Root soil interface in agroforestry systems. In: Agboola, A. A., Sobulo, O., and Obatolu, C.R. (eds) proceedings of the third African soil scie nce society conference, Lagos, Nigeria, pp. 201-210. Balee W. and Gely A., 1989. Managed Fore st Succession in Amazonia: The Kaapor Case. Advances in Economic Botany. 7, 129-158. Behrens, C.A., Baksh M.L. and Mothes M., 1994. A Regional Analysis of Bari Land Use Intensification and its Impact on La ndscape Heterogeneity. Human ecology 22, 279-316. Belize Meteorology Service, Hydrology Depart ment. Personal communications (2006). http://www.hydromet.gov.bz.

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48 Bermejo, I., Canellas, I., San Miguel A ., 2004.Growth and yield models for teak plantations in Costa Rica. Fore st Ecology and Management 189, 97 Bertoni G., Morard P., 1982. Blade or petiol e analysis as a guide for grape nutrition. Commun in Soil Sci. Plant Anals, 13, 593-605. Binkley, D., Senock, R., Bird, S., Cole, T.G ., 2003. Twenty years of stand development in pure and mixed stands of Eucalyptus saligna and nitrogen-fixing Facaltaria moluccana. Forest Ecology and Management 182, 93. Binkley, D., O'Connell, A.M., Sankaran, K.V., 1997. Stand development and productivity. In: Nambiar, E.K.S., Brown, A.G. (Eds.), Management of Soil, Nutrients and Water in Tropical Plan tation Forests. ACIAR/CSIRO/CIFOR, ACIAR, Canberra, Australia, pp. 419-442. Binkley, D., Dunkin, K.A., DeBell, D., Ryan, M.G., 1992. Production and nutrient cycling in mixed plantations of Eucalyptus and Albizia in Hawaii. For. Sci. 38, 393-408. Boot R.G.A., 1997. Extraction of non-timber fore st products from tropical rain forests: Does diversity come at a price? Nether lands Journal of Agricultural Science 45, 439-450 Boserup, E., 1965. The Conditions of Agricultu ral Growth: The Economics of Agrarian Change Under Population Pre ssure. Chicago: Aldine. Brady, N.C. and Weil R.R., 2002. The Nature and Properties of Soils. Prentice Hall Publisher. Upper Saddle River, NJ. Brondzio, E. S., and Siqueira, A. D., 1997. Fr om Extractivists to Forest Farmers: Changing Concepts of Agricultural Intens ification and Peasantry in the Amazon Estuary. Research in Economic Anthropology. 18, 233. Brondizio, E.S., Moran E.F., Mausel P. and Wu, Y., 1994. Land use Change in the Amazon Estuary: Patterns of Caboclo Settlement and Landscape Management. Human Ecology. 22, 249-278. Bruijnzeel, L.A., 1984. Immobilizat ion of nutrients in plantati on forests of Pinus merkusii and Agathis damara growing on volcanic soils in central Java, Indonesia. In: Tajib, A., Pushparajah, E. (Eds.), Proc. Int. C onf. on Soils and Nutrition of Perennial Crops. Malaysian Soil Science Society,Kuala Lumpur, pp. 19-29. Bruntland G.H., 1989. Notre avenir tous. ditions du Fleuve. Qubec, Canada. Bruntland Commission, 1987. Our Common Future. The World Commission on Environment and Development. Oxford University Press. Oxford, United Kingdom.

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49 Cadish, G., Ndufa, J.K., Yasmin, K., Mut uo, P., Baggs, E., Keerthisinghe, G., and Albrecht, A., 2002b. Use of stable isotope s in assessing belowground contributions to N and soil organic matter dynamics in: International union of soil science, the soil and fertilizer society of Thailand, Mi nistry of agriculture and cooperatives of Thailand (eds) 17th World Soil Science Conference S oil Science: confronting new realities in the 21st century. International soil science society, Bangkok, Thailand, CD-Paper No.1165, pp. 1-10. Cannel, M., Van Noordwijk, M., and Ong C., 1996. The central agrofo restry hypothesis: The trees must acquire resources that the crop would not otherwise acquire. Agrofor. Sys. 34, 27-31. Chapin S.F., Matson, P.A., Mooney H.A., 2002. Principles of ecosystems ecology. Springler-Verlag, New York. Cornelius J.P., Watt A.D., 2002. Ge netic variation in a Hypsipyl a-attacked clonal trial of Cedrela odorata under two pruning regime s. Forest Ecology and Management 183, 341. Conklin, H. C., 1957. Hanunoo Agriculture: A Repor t of an Integral System of Shifting Cultivation in the Philippines. Rome: United Nations Food and Agricultural Organization. Cogger C., 2000. Soil Management for Small Farmers. Farmers West of the Cascade Series. Food and Farm Connection. Pp 1 24. Coolman, R.M. and Hoyt, G.D., 1993. In creasing sustainability by intercropping. HortTechnology, 3, 309-312. Cusack, D. and Montagnini F., 2004. The role of native species plantati ons in recovery of understory woody diversity in degraded past urelands of Costa Rica. Forest Ecology and Management 188, 1. Dinesh, R., Ghoshal Chaudhuri, S. Ganesham urthy A.N., Chanchal D., 2003. Changes in soil microbial indices and their relationships following deforestation and cultivation in wet tropical forests. Applied Soil Ecology 24, 17. Dommergues, Y.R., Subba Rao, N.S., 2000. Intr oduction of N2-fixing trees in non-N2fixing tropical plantation s. In: Subba Rao, N.S., Dommergues, Y.R. (Eds.), Microbial Interactions in Agriculture a nd Forestry, vol. II. Science Publishers, Enfield, NH, USA, pp. 131. Dunisch, O., Montoia, V.R., Bauch J., 2003. Dendroecological investigations on Swietenia macrophylla King and Cedrela odorata L. (Meliaceae) in the central Amazon. Springer-Verlag. Trees 17, 244

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50 Dunisch O, Bauch J, Gasparotto L., 2002a. Cambial growth dynamics and formation of increment zones in the xyle m of Swietenia macrophylla King, Carapa guianensis Aubl., and Cedrela odorata L. (Meliaceae). IAWA J 23, 101. FAO, 2001. Global Forest Resources Assessm ent, 2000, Main Report. FAO Forestry Paper No. 140, Rome. FAO, 1997. State of the Worlds Forests 1997. Food and Agriculture Organization of the United Nations, Rome, Italy, 200 pp. Finch S; Collier R., 2000. Host-plant se lection by insects a theory based on appropriate/inappropriate landings by pe st insects of cruciferous plants. Entomologia Experimentalis et Applicata 96, 91-102. Folster, H., Khanna, P.K., 1997. Dynamics of nutrient supply in plantation soils. In: Nambiar, E.K.S., Brown, A.G. (Eds.), Mana gement of Soil, Nutrients and Water in Tropical Plantation Forests. ACIAR/CSIR O/CIFOR, ACIAR, Canberra, Australia, pp. 338-378. FRA, 2000. Annotated Bibliography Forest Cove r Change Belize. Forest Resources Assessment Programme. Working Paper 40 Rome, 2000. Gathumbi, S.M., 2004. Root recovery of five tr opical tree and shrub species by sieves of different mesh sizes. Agrofor. Sys. 60, 233-237 Gholz, H.L, 1987. Agroforestry: Realities, Possibilities and Po tentials. Dordrecht: Martinus Nijhoff Publisher. Goncalves, J.L.M., Barros, N. F., Nambia r, E.K.S., Novais, R.F., 1997. Soil and stand management for short-rotation plantati ons. In: Nambiar, E.K.S., Brown, A.G. (Eds.), Management of Soil, Nutrients and Water in Tropical Plantation Forests. ACIAR/ CSIRO/CIFOR, ACIAR, Ca nberra, Australia, pp. 379-417. Government of Belize, 1996. Belize Abstracts of Statistics. Centra l Statistical Office, Ministry of Finance, Belmopan, Belize. Guillet D., 1987. Agricultural Intensification a nd Deintensification in Lari, Colca Valley, Southern Peru. Pg 201-224 in B. Isaac (ed.) Research in Economic Anthropology Vol.8 Greenwich, Ct. JAI Press. Harrison, P., Mattos, M. and Uhl C., 1995."A profile of palm hear t extraction in the Amazon estuary." Human Ecology: An Interdisciplinary Journal 23, 357-385. Hiremath, Ankila J., Ewel, John J., and Cole Thomas G., 2002. Nutrient Use Efficiency in Three Fast-Growing Tropical Trees. Forest Science 48, 662-672. Hiebsch, C., and McCollum, R., 1987. AreaX-time equivalency ratio: A method for evaluating the productivity of intercrops. Agron. J. 79, 15-22

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55 The world fact book. http://www.cia.gov/cia/public ations/factbook/geos/bh.html (02/21/07). Trenbath, B.R., 1976. Plant interaction in mi xed crop communities. In Papendick, R.I., P.A. Sanchez and G.B. Triplett (eds.), Multiple Croping. ASA special publication no. 27. Amer. Soc. Agron., Modison, WI, USA. pp 129-170. Turner, B.L. and Brush S.B., 1987. Compar ative Farming Systems. New York: The Grifford Press. Unwin G.L., Jennings S.M., Hunt M.A., 2006. Light environment and tree development of young Acacia melanoxylon in mixed-species regrowth forest, Tasmania, Australia. Forest Ecolog y and Management 233, 240. Vandermeer J., 1989. The Ecology of Intercropping. Cambridge University Press, Cambridge. Wadsworth, F.H., 1997. Forest Production fo r Tropical America. United States Department of Agriculture Forest Se rvice. Agriculture Handbook 710. Washington, DC. Wang, D., Bormann, F.H., Lugo, A.E., Bowde n, R.D., 1991. Comparison of nutrient-use efficiency and biomass produc tion in five tropical tree ta xa. For. Ecol. Manage. 46, 1-21. Watts, M. J., 1987. Powers of Production-Geographers among Peasants. Environment and Planning D 5, 215-230. Wilken G.C., 1987. Good Farmers. Traditiona l Agricultural Resource Management in Mexico and Central America. Berkeley : University of California Press. Wolf, B., 1982. Communications in So il Science and Plant Analysis. 13, 1035-1059. Library of Congress Cata log Card Number 70-20238. Worbes M., 1999. Annual growth rings, rainfall dependent growth and long-term growth patterns of tropical trees from the Forest Reserve Caparo in Venezuela. J Ecol 87, 391-403. Wormald, T.J., 1992. Mixed and pure forest plan tations in the tropics and subtropics. FAO Forestry Paper 103. FAO, Rome, p. 152. Zimmerer, K.S., 1996. Changing fortunes bi odiversity and peasant livelihood in the Peruvian Andes. Berkeley, CA: University of California Press. Zisman Simon, 1996. The Directory of Belizean Protected Areas a nd Sites of Nature Conservation Interest.

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56 BIOGRAPHICAL SKETCH Juanita Garcia-Saqui was born in Stann Creek, Belize C.A. She is the fourth daughter and fifth child born to Reverend Juana Garcia-Gut ierrez and Jorge Garcia. Juanita Garcia began her education at the Light of the Valley Baptist Primary School. Because of financial constraints, Juanita had to stay out of school for two years before entering high school. Therefore after two years following the Baptist Primary School, she was enrolled at the Ecumenical High School. In 1992, she graduated from Ecumenical High School, and because of financia l constraints, she was forced to enter the work force. She worked for six years, after which she returned to the University of Belize in 1999 where she obtained an associat es degree in natural resources management in 2001. After her associates degree, Juanita pursued and obtained a b achelors degree in biology in 2003. While pursuing her bachelors degree, Ju anita also worked as an assistant laboratory technician for the Micro propagati on laboratory at the Un iversity of Belize, where she assisted in the tissu e culturing of native orchids of Belize. After obtaining her bachelors degree Juanita took full respons ibility of the micro propagation laboratory and worked appointed by the University of Be lize as a consultant fo r the OAS project in Belize which is affiliated with the University of Belize. In 2004, Juanita was accepted with funding to the University of Florida in the School of Natural Resources and Environment, where she majored in interdisciplinary

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57 ecology with a concentration in forest re sources and conservation. Juanita has been married to Mr. Pio Saqui for eight years.