Open Journal of Forestry 2018, 8, 114 http://www.scirp.org/journal/ ojf ISSN Online: 21630437 ISSN Print: 21630429 DOI: 10.4236/ojf.2018.81001 Nov. 23, 2017 1 Open Journal of Forestry Water Use of Juvenile Live Oak ( Quercus virginiana) Trees o ver Five Years in a Humid Climate Richard C. Beeson1, Hang Thi Thu Duong2, Roger Kjelgren2 1Dep ar t ment of Horticultural Sciences, Institute of Agricultural Sciences Mid Florida Research and Education Center, University of Florida Apopka, F L, USA 2Dep ar t ment of Environmental Horticulture, Institute of Agricultural Sciences Mid Florida Research and Educa tion Center, University of Florida Apopka, F L, USA Abstract To meet minimum spring flows, water management districts in Florida sought to make both agriculture and urban landscapes water efficient, which includes tree farms. Quercus virginiana, commonly known as live oak tre es, is endemic to Central Florida and among the most popular landscape trees for their gracefulness and spreading shade. To provide a basis for irrigation allocations both during production and in landscapes, daily actual evapotranspiration (ETA) in liters for t hree live oak trees w as measured with weighing lysimeters over five years, beginning with seedlings and continuing until trees averaged 7.2 meters in height. Empirical models were derived to ca lculate ETA based on crown horizontal projected area (PCA) or t runk caliper (TCSA), adjusted daily by changes in evapotranspiration (ETO). Average ETA to produce these live oaks was 62,218 L cumulative over 5.5 years. Effectively transpiring leaf, tree water use volume divided by ETO, was closely related to PCA over f ive years with the slope of this relationship being equivalent to a Plant Factor of 0.93. The product of ETO and this Plant Factor can be used to estimate depth of live oak water demand in urban landscapes. Also, this Plant Factor can estimate water demand volume in nurseries and landscapes when combined with PCA, and similarly the slopes for TCSA can be used to estimate ETA water volume from measured trunk diameter. Keywords Quercus v irginiana, I rrigation S cheduling, I rrigation M odelling, C ontainer P roduction, L andscape I rrigation How to cite this paper: Beeson, R C. Duong, H T T & Kjelgren R (201 8 ) Water Use of Juvenile Live Oak ( Quercus virginiana ) Trees over Five Years in a H umid Climate Open Journal of Forestry 8 1 14 https: // doi.org/10.4236/ojf.2018.81001 Received: October 10, 2017 Accepted: November 2 1 2017 Published: November 2 4 2017 Copyright 201 8 by authors and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0 ). http://creativecommons.org/licenses/by/4.0/ Open Access
R. C. Beeson et al. DOI: 10.4236/ojf.2018.81001 2 Open Journal of Forestry 1. Introduction Trees planted in urban landscapes often require irrigation during all stages of life: during production in containers or as large specimens (Beeson, 1992; Beeson & K eller, 2003) during root system establishment post transplanting (Gilman, Black, & Dehgan, 1998) in arid climates (Lindsey & Bassuk, 1991) or during drought once established in humid climates. Landscape tree water management requires reasonable estimates of water demand in order to schedule irrigation amounts and timing to conserve water while maintaining tree health. Estimating tree w ater demand is not straightforward. Water demand of isolated trees as typically found in urban landscapes is affected by numerous factors: developmental stages, nutrition, spacing and shading within species, b ut the overriding ar e tree size and shape, and transpiration rate (Burger et al., 1987; Fitzpatrick, 1980, 1983; Knox, 1989) Defining tree water use terms is critical: we define measured tree evapotran spiration in volume units of liters (L) day 1 as whole tree water use (ETA). Fu rther, we define calculated tree transpiration rate in depth units of mm day 1 as tree water use rate. Tree water use rate is almost always a derived number calc ulated from measured ETA divided by some measure of total area of transpiring leaves (Kjelgren, Beeson, Pittenger, & Montague, 2016) Tree water use rate is typically used in planning or scheduling sprinkler irrigation as water depth, and ETA is used in scheduling irrigation of trees irrigated with drip systems that a pply water volume. Fi nally, we define tree water demand as either volume or depth of tree water use estimated from empirically derived constants or variables b ecause measuring tree water use rate (mm day 1), ETA (L day 1) or transpiring leaf (m2) is impractical. Here we have m easured ETA with lysimeters and appro ximated transpiring leaf as the variable, projected crown area (PCA), to derive a Plant Factor, a constant that links the practical use of tree water demand estim ation to the most widely accepted variable in managing pl ant irrigation, reference (or potential) evapotranspiration ( ETO; Allen et al., 2005 ). ETO integrates the weather factors of solar radiation, wind, ambient humidity, and air temperature which drive evaporative pull on leaves for a hypothetical clipped cool season turf, allowing standard measure of potential water demand among places and b etween times (Allen et al., 2005) The literature review of Wullschl eger, Meinzer, & Vertessy (1998) reported ETA ranging from 10 to 200 L day 1, mostly based on differences in canopy size and transpiring leaf area. Most studies have quantified whole tree evapotransp iration for relatively short periods of time, typically much less than a year or o ften shorter. Ruiter (1987) studied ETA of Pinus radiata (radiata pine) using large drainage lysimeters with volumes of 7 m3. After three years, trees irrigated throug hout the period averaged 3 4 m in height, with daily average ETA over four weeks of 21 L day 1. Edwards (1986) measured daily ETA of single trees of four species grown in southern New Zealand for a year. At termination, trees ranged from 3.3 to 5.6 m in height. ETA exceeded 120 Lday 1 in summer for Ecualyp u-
R. C. Beeson et al. DOI: 10.4236/ojf.2018.81001 3 Open Journal of Forestry tus fastigata, and was near zero for deciduous species during winter. Beeson (2016) quantified average ETA of three Acer rubrum trees using weighing lys imeters (Beeson, 2011) from small liners to 8 m tall trees over five years in Ce ntral Florida. Total average volume of three trees was 29,107 L cumulative over nearly five years. During the summer months of the last year, ETA peaked at 101 Lday 1. In an experiment of five species of containerized woody plants, Knox (1989) described the primary factors driving whole tree water use as transpiration rates and size. In Central Florida Beeson (1993) compared water use rate (mm day 1) of container grown (10.2 L) Rhododendron sp. Formosa to water demand e stimated from the ETO (PenmanMonteith equation, cool season turfgrass refe rence) corrected by a Plant Factor. The study noted that poor correlations b etween estimated demand and measured water use rate can be improved by more frequent canopy measurements to capture size changes during periods of rapid growth. Devitt, Morris, & Neuman (1994) measured ETA of three woody orn amentals in order to improve water demand estimates of Prosopis alba Grisebach, Chilopsis linearis (Cav.) Sweet var. linearis and Quercus virginiana Mill. in N evada. They found ETA of oak was closely correlated to all measured growth p arameters, defined as height, di ameter, and canopy volume. St.Clair (1994) suggested that water use be estimated from trunk diameter. Although ETA was related to trunk diameter, the relationship was nonlinear. Sim pson (2000) reported that ETA in Lday 1 was related to the cross sectional sap wood area, a more finely tuned measure of xylem water conducting capacity than trunk diameter. However sapwood area depends on tree species and tree age. For Acer rubrum, a diffuse porous species, correlati on between ETA and trunk cross se ctional area was shown to be valid for trees up to 100 years of age (Gebauer, Horna, & Leuschner, 2008) But for a ring porous species, such as Quercus sp., this rel ationship may only be valid for young trees (Greenridge, 1955; Kozlowski & Wi nget, 1963) Quercus sp. are ring porous, so may have a lower correlation between ETA and trunk cross sectional area in mature trees (Kramer & Kozlowski, 1979) Stem cross sectional area can still be an easily measured estimate of leaf area, and so useful in estimating whole plant water use. Weighing lysimeters are the most precise tool for empirically measuring whole plant water use, and so the basis for developing Plant Factors that combine with ETO to estimate tree water demand in nurseries and landscapes. Most tree water use studies have been conducted in semi arid to arid climates; much less so in humid climates. More information on estimating tree wat er demand in humid climates, either as a rate or as a volume, can aid nursery and landscape water managers and policy makers in humid regions, especially in subtropical climates with lengthy dry seasons. Our objective was to use tree water use v olumes (ETA) measured from lysimeters to model evapotranspiration rates with measures of tree size such as projected canopy area and trunk cross sectional areas of live oak, a common landscape tree in warm temperate and sub tropical
R. C. Beeson et al. DOI: 10.4236/ojf.2018.81001 4 Open Journal of Forestry climates. Findings presented here are daily mean ETA and growth of three ind ividual oak trees beginning from seedlings to 7.2 m tall trees over nearly six years. The objective of this study was to develop Plant Factors from measured ETA (v olume unit) and ETO. Here we used easily measured tree traits that control tran spiration, projected canopy area and trunk cross sectional area, such that whole tree water demand can be estimated for improved water management in nursery production and irrigated landscapes. 2. Materials and Methods 2.1. Exp erimental Setup 2.1.1. Transplanting Live oak seedlings (Quercus virginiana) were obtained late winter 2001from a nursery in north Central Florida. Seedlings were relocated 75 Km east of the nu rsery to within the Orlando, Florida Metropolitan area (28.54 l atitude and 81.38 longitude). Five seedlings were transplanted into 26 L containers using a 70% co mposted pine bark: 30% Florida sedge peat: 10% coarse sand substrate amended with 0.68 kg per m3 of micronutrients Micromax (Scotts Company, Marysville, OH) and 2.3 kg per m3 of dolomite limestone to buffer to a pH of 6.0. In years 2004 2005, NuPeat, composed from one third composted yard waste, one third composted and screened hardwood bark, and one third Florida sedge peat, r eplaced existing sedge peat. Thes e five containers were painted inside with a latex paint mixed with copper (Spin out, Griffin Corp, Vadosta, GA) and the outside covered with aluminum foil to reduce excess container heating and surface evaporation. These containers were also covered with a shallow convex dome to e xclude most rainfall and to reduce evaporation from the container substrate. Each subsequent study year, trees were planted during late winter into sequentially larger containers, with the same substrate, fertilization, and contai ner prep fo llowed. In 2002, trees were transplanted in 95 L container (0.55 m diameter), then in each subsequent year 2002 2005 trees were progressively moved into 361 760, and 1140 L containers. In 2003 an appropriately sized wire basket (32 COT, Cherokee Manufacturing Inc., St. Paul, MN) was placed in containers to mai ntain root ball integrity while lifting trees during replanting into larger containers without causing damage to trunks. 2.1.2. Tree Care Trees were staked, pruned, and fertilized as needed using controlled release fert ilizer (Polygon 19N4.2P 11.6K, Harrells Fertilizer Co. Lakeland, FL). Starting in 2002, overall tree canopies were pruned to promote tree structure in accordance with Florida Grades and Standards for Nursery Crops mid to late winter (Flor ida Department of Agriculture and Consumer Services, 1998) In 2003, after transplant ing, trees were pruned to raise the bottom of tree canopies to 1.2 m above the root ball. 2.2. Experimental Layout The first year, five s tudy trees were suspended from a 2 m high tripod lysimeter
R. C. Beeson et al. DOI: 10.4236/ojf.2018.81001 5 Open Journal of Forestry (Beeson, 2011) which consisted of a basket to hold the container suspended from a load cell (SSM 100, Interface Force Inc., Scottsdale, AZ) underneath the tripod. Load cells we re connected to a data logger (CR10X, Campbell Scientific, Inc., Logan, UT) and multiplexer system (AM 416 and AM 32) that collected lysim eter mass every half hour and controlled irrigation (Beeson, 2011) In 2002, the three largest tr ees were placed singly in large weighting lysimeters (Beeson, 2011) in a row oriented east west. Each triangular lysimeter basket was suspended from three 341 kg load cells (SSM 750, Interface Force Inc., Scottsdale, AZ) attached to st eel pillars at apices. A basket accommodated up to a 1.55 m diameter poly ethylene container. Study trees remained in the triangular lysimeters from 2002 through 2006. Spacing of border trees each spring was representative of nursery production at each stag e of growth. In 2001 trees were 0.4 m on center using a square a rrangement with 95 border trees handled and transplanted the same as the study trees. Lysimeters were randomly placed within a middle row in the block of four rows of 25 containers. In 2002, 1 8 border trees were transplanted into containers similar to those of the study trees and placed around each triangular lysimeter study tree to maintain tree canopy cover, which provided an initial canopy de nsity of 50%, approximating that of a commercial nursery. In 2003, border trees were reduced to 12 per lysimeter to maintain 50% canopy density. In 2004, the number of border trees around each lysimeter was reduced to six to maintain constant canopy density. In 2005, one border tree was placed in the four cardinal directions around each lysimeter, with one tree between lysimeters within the row. 2.3. Irrigation The first year, five study trees were suspended from a 2 m high tripod lysimeter (Beeson, 2011) which consisted of a basket to hold the container suspended from a load cell (SSM 100, Interface Force Inc., Scottsdale, AZ) underneath the tripod. Load cells were connected to a data logger (CR10X, Campbell Scientific, Inc., Logan, UT) and multiplexer sy stem (AM 416 and AM 32) that collected lysim eter mass every half hour and controlled irrigation (Beeson, 2011) In 2002, the three largest trees were placed singly in large weighting lysimeters (Beeson, 2011) in a row oriented east west. Each triangular lysimeter basket was suspended from three 341 kg load cells (SSM 750, Interface Force Inc., Scottsdale, AZ) attached to steel pillars at apices. A basket accommodated up to a 1.55 m diameter poly ethylene container. S tudy trees remained in the triangular lysimeters from 2002 through 2006. Spacing of border trees each spring was representative of nursery production at each stage of growth. In 2001 trees were 0.4 m on center using a square arrangement with 95 border tree s handled and transplanted the same as the study trees. Lysimeters were randomly placed within a middle row in the block of four rows of 25 containers. In 2002, 18 border trees were transplanted into containers similar to those of the study trees and place d around each triangular lysimeter
R. C. Beeson et al. DOI: 10.4236/ojf.2018.81001 6 Open Journal of Forestry study tree to maintain tree canopy cover, which provided an initial canopy de nsity of 50%, approximating that of a commercial nursery. In 2003, border trees were reduced to 12 per lysimeter to maintain 50% canopy density. In 2004, the number of border trees around each lysimeter was reduced to six to maintain constant canopy density. In 2005, one border tree was placed in the four cardinal directions around each lysimeter, with one tree between lysimeters within the row. 2 .4. Climate Conditions Climatic conditions in Centr al Florida during the 5 year the experiment w ere conducted as considered normal. During January to mid March, temperatures normally ranged from 4 C to 20C most days with mostly sunny conditions. Temperatu res below freezing were infrequent, but occurred. From late March late May, sunny skies continued, with infrequent rain storms and rapidly i ncrease in temperatures. In late May, temperatures ranged from 24 C to 32 C with frequent thunderstor ms that continued to mid October. From mid October to late November, temperature ranges were similar to spring, with night tempe ratures dropping below 5 C and occasional freezes. During this 5 year period, se veral hurricanes impacted the research site with some le af loss. 2.5. Data Collection 2.5.1. Reference Evapotranspiration Reference evapotranspiration (ETO) was calculated each day from a Campbell Scientific (Logan, UT) weather station located in a grassy field 25 m west of l ysimeters. The weather station consi sted of a pyranometer (Li 200; Li Cor Inc., Lincoln, NE), a tipping bucket rain gauge (TE525, Texas, Instruments, Dallas, TX), temperature/humidity sensor (CS 215, Campbell Scientific Inc., Logan, UT), a wind sensor (Model 014, Met One Instruments, Grants Pass, OR), and a CR10X data logger that used Application Note 4 (Campbell Scientific Inc.) to calculate ETO with resistance as described by Allen, Jensen, Wright, & Burman (1989) 2.5.2. Growth Measurements Growth measurements of tree height, branch spread of widest width and width perpendicular, and maximum trunk caliper at 0.15 m and 0.30 m above the su bstrate were recorded on lysimeter trees every three weeks during each growing season for the first three years. Beginning year three, trunk circumference was measured with a metal tape measure. At the beginning of the last third of year two, trunk circumference measurements were initiated at 1.2 m above the su bstrate. Horizontal Projected Canopy Area (PCA, m2) was calculated by multi ply ing consistent perpendicular measurements of branch spread, north south and east west. Trunk cross sectional area (TSCA, cm2) was calculated for each of three trunk measurement based on trunk circumference; where circumference divided by 6.284 (= 2*) equal s trunk diameter. Diameter divided by 2, then multiplied
R. C. Beeson et al. DOI: 10.4236/ojf.2018.81001 7 Open Journal of Forestry by 9.689 (2) equalizes cross sectional area was calculated as: Area = radius2 ( http://www.sengpielaudio.com/calculator cr oss section.htm ). 2.5.3. Water Use Usually ETA was calculated daily as differences between mass recorded at 6:00 am minus mass recorded at 10:00 pm. When partial midday irrigation was in e ffect, increases in mass from midday irrigation was calculated by the datalogger and added to the daily sum. However, if rare loss of power or common rain events occurred between 6:00 am and 10:00 pm, actual daily cumulative ETA was est imated as described by Beeson (2006) For power loss, each trees daily ETA b e fore and after the loss was normalized to water volume per unit ETO (Norm a lized ETO, L mm 1). This assumed leaf area was constant and normalized values varied minimally over short periods of four to seven days without precipitation. Daily ETA for each missing day was estimated by multiplying the Normalized ETO v olume by the measured ETO for each missing day. When rainfall occurred b etween 6:00 am and 10:00 pm, half hour mass data was plotted to indicate rainfall events. Periods of decreases in mass were summed to estimate ETA. This was then vetted by normalizing by ETO, then comparing the rain day normalized ETA to normalized ETA of recent rainless days. 2.6. Data Analysis Daily volumetric water use and average daily air temperature were plotted over the growing season for each year. Measurements of tree cross sectional areas that control transpiration (PCA and TSCA at three heights, in m2) were regressed against corresponding Normalized ETA (N ETA; ETA ETO in liters mm 1) on days trees were me asured. PCA and TSCAs were averaged each quarter each year and plotted over growing season throughout 5.75 years. Pooled standard deviation for three trees was calculated for eac h quarter. Linear regression was analyzed in R 3.4.1 using simple linear regression model. 3. Results 3.1. Quantifying ETA Live oak is a mediumfast growth evergreen tree under well irrigated conditions. Trees grew from 0.22 m to 7.18 m tall over 5.75 years with an average increase of 1.30 m/year in height for the first 3.75 years, and a slower increased height of 1.0 m/year for the last 1.75 years. Leaf habit is evergreen, with leaves slowly shedding, buds bursting and leaves expanding on spur shoots for several weeks in February to early March, with first major shoot elongat ion occurring usually in mid April, thus leaf area was relatively constant or increasing throughout the experiment. Bell shaped variations in ETA over a year are therefore reflective of three distinct shoot flushes and changes in weather temperature, sun, humid ity, and day length which drove ETO, along with changes in leaf accumulation. These bell shapes had longer tails during winter and early spring due to lower
R. C. Beeson et al. DOI: 10.4236/ojf.2018.81001 8 Open Journal of Forestry temperatures, solar radiation, and leaf change, covering the approximate first third of each y ear. As shown in Figure 1 ( a ) the height of the bell shapes i ncreased over years due to the leaf area increases throughout the experiment. In an area with high humidity such as Florida, seasonal changes in ETA reflect t empe rature changes rather than that of solar radiation. Figure 1 ( b ) shows changes in daily average temperature throughout the experiment. Year 1, trees grew from 0.22 m to 1.58 m tall, and from 0.11 m to 0.57 m in average canopy spread by the end of December. ETA gradually increased from mid April (around day 100), peaked at the end of July and mid October, and then gradually declined from mid October onward. Mean cumulative ETA from April to December for 2001 was 123.7 L with daily ETA as 0.46 L d ay 1 (data not shown). Year 2, trees initiated bud break in mid February, concurrent with slow defoliation of the previous leaves, followed by a large leaf flush from early May to mid August. There was an other full leaf flush from mid September to early October. Tree height increased from 1.59 to 2.94 m and average canopy spread increased from 0.57 m to 1.83 m. Mean cumulative ETA for the entire year was 1395.6 L, with daily ETA greatly increased to 3.8 Lday 1, as shown in Figure 1 ( a ) Year 3, initial bud break occurred again in early February, with first spur leaf flush occurring as in previous years, in mid February; the second full leaf flush occurred from early to late May. ETA in the third year was approximately three fold larger than that of the second year, increasing to 13.52 Lday 1, with a mean cumulative ETA of 4933.75 L. Trees grew from 2.94 m to 4.26 m tall and from 1.54 m to 2.81 m in average canopy spread. Year 4, bud break began in early February with three full leaf flushes from mid to late March, early to mid May and early July to early August. Trees grew from 4.31 m to 5.46 m tall and from 2.81 m to 3.73 m in average canopy spread. Daily ETA doubled to 3,166 Lday 1 co mpared to the previous year. Figure 1 ( a ) shows mean cumulative ETA for the fourth year was 11,586.7 L. Bud break and duration varied slightly from year to year. Year 5, transition bud break began in March, with the first full leaf flush lasting a month starting in early April and the second full leaf flush occurred in early June to late June, extending to late July. Trees averaged from 5.90 m to 6.54 m in height and from 3.81 m to 4.62 m in average canopy spread by the end of D ecember. As shown in Figure 1 ( a ) daily ETA for the fifth year again more than double that of the fourth year to 59.21 Lday 1 with a mean cumulative ETA of 21,612.84 L. In the last year, until August when the trees were harvested, the height reached 7.18 m and average canopy spread to 4.85 m, with cumulative ETA of 22,565.49 L, and daily ETA of 93.63 Lday 1. 3.2. Modelling Daily ETA Projected Canopy Area (PCA) and Trunk Cross Sectional Areas (TCSA) were ca lculated at 0.15 m, 0.3 m, and 1.2 m and, as shown in Figure 2 steadily increased over time. PCA slightly decreased or was level in the first quarter each year b ecause trees were pruned during late February to early March, depending on the year. Thereafter growth quickly recovered.
R. C. Beeson et al. DOI: 10.4236/ojf.2018.81001 9 Open Journal of Forestry Figure 1. Mean daily ETA of Quercus virginiana (live oak) and mean daily temperature in Apopka, Florida from 2001 to 2006. Note. ( a ) Each point is based on the mean of three trees replicates ; (b) D ata obtained from FAWN: Florida Automatic Weather Network. (a) (b) Figure 2. Average quarterly projected canopy area (a) and trunk cross sectional (b) for Quercus viriginia. Note: for both (a) and (b) each point is the average of three tree replicates; (b) measured 0.15 m, 0.30 m, and 1. 2 m at the first major branch above the soil. N ETA was closely and linearly related to the four measures of tree size (r2 0.85 and Pr(>F) = 2.26e 16 for all four relationships; Figure 2 ). Algebraically rearranging the fitted Equation (1) to solve for ETA yields: 2mmarea coefficientEstimated litersPlant FactorslopeareamoAETET 3. 3 Discussion Tree growth resulted in about 1.0 m to 1.3 m of height growth each year. Long growing seasons in Central Florida likely compensated for shorter days (14 hr
R. C. Beeson et al. DOI: 10.4236/ojf.2018.81001 10 Open Journal of Forestry Figure 3. Relationships of n ormalized ETA over 6 years to four measures of horizontal surface areas. Horizontal projected canopy area, (b) Trunk cross sectional areas at 0.15 m, 0.30 m, and 1.2 m ( first major branch ) above the soil of Quercus viriginia to estimate da ily ETA. The P value Pr(>F) = 2.26e16, was the same for all four relationships. maximum) and warmer nights compared to northern latitudes. ETA of the live oak trees was maintained quite low for 2 3 months of winter due to relatively low temperatures (20 C to 25 C daily Tmax; 10 C to 15 C Tmin) and low solar radiation which resulted in slow growth of trees. ETA gradually increased in spring with bud break with warmer temperatures (25 C to 30 C daily Tmax; 20 C to 23 C Tmin) and longer days, increasing ETO from average 2.6 mm day 1 in winter to 5.05 mmday 1 in spring, as shown in Figure 1 The bell shaped pa ttern of ETO tightly reflects seasonal variability in temperature of the northern hemisphere. The result is in contrast with deciduous maple tree reported by Beeson (2016) that daily ETA rapidly declined due to shoot growth termination even though ETO remained fa irly consistent into September. Water use of Quercus sp. reveals important relationships to environmental condition s that have not been previo usly reported. Compared to other previous ly reported landscape trees, ETA values of live oak trees were similar in the first five years at the height of 6.5 m, but much higher in the sixth year (93.63 L day 1) at the height of 7.2 meters. Pausch, Grote, & Dawson (2000) reported daily ETA rates of 61 to 72 Lday 1 for Acer saccharum in forest near Ithaca, NY for 24 cm DBH trees. Under similar conditions and experimental setup, red maple trees (Acer rubrum L.) in Florida average ETA was 29,107 L cumulative over nearly five years for trees 0.4 m to 8 m tall (Beeson, 2016) and cumulative holly (Ilex spp.) ETA was 20.461 L per tree over nearly six years from 0.3 m to 4.3 m tall (Bees on, Duong, & Kjelgren, 2017 ) Whereas cumulative ETA of live oak over nearly six years was 3 fold higher than that of holly at 62,218 L for trees 0.22 m to 7.18 m tall. Given the data here, and that leaf area and sapwood area are generally closely related, sapwood area can serve as a predictor of volumetric water demand for individual trees, even for a ring porous species such as live oak, either directly as a variable when combined ETO and an appropriate Plant Factor (see Equation ( 1 ) ), or used to estimate PCA, which could then be used in Equation ( 1 ) In a study of water use of Interior West Douglas fir (Pseudotsuga menzezii var. glauca ) in a nat-
R. C. Beeson et al. DOI: 10.4236/ojf.2018.81001 11 Open Journal of Forestry ural environment, Simpson (2000) found that for small trees a large p ortion of basal area (total crosssectional area of stem at 1.5 m) was sapwood area. Similarly, Sellin (1991) found for a 10 year old dominant Norway spruce (Picea abies (L.) Karst. ) that approximately 95% of the stem cross sectional area was conduc ting sapwood and so contributing to whole plant water use. PCA or TCSA, ther efore, can be a relatively good indicator of maximum whole plant potential water use for individual trees when combined with ETO and a Plant Factor ap propriate to PC A or TCSA. A key point of this study is that the slope of the relationship between N -A, which is an estimate of transpiring leaf area after variability from ETO is factored out, and PCA is equivalent to the Plant Factor described by Kjelgren et al. (2016) Past tree water use studies often divided ETA by laboriously harvested total leaf area that may not be the best measure of transpiring leaf area. Harvested total leaf area will include many leaves that are shaded over the course of a day, esp ecially species with dense crowns, so would contribute little to ETA. PCA is pe rhaps a less precise measure than TCSA but is probably a simpler and practical means to estimate transpiring leaf area, and with a proper Plant Factor, a more useful way to estimate volumetric tree water demand. Correlation between N ETA with PCA and TCSA at heights of 0.15 m, 0.30 m, and 1.2 m of the oak trees was high, r2 0.85 Pr(>F) = 2.26e 16, was the same for all four relationships, and similar to the relationships between ETA and the same growth parameters that were found for red maple (Beeson, 2016) and holly (Beeson et al., 2017) Trunk diameter is closely correlated with tree size and leaf area (Mart in, Kloeppel, Schafer, Kimbler, & McNulty, 1998; Simpson, 2000; Ve rtessy, Benyon, OSullivan, & Gribben, 1995) of diffuse porous species because co nducting xylem area is continuous and proportional to transpiring leaf area, and so leaf area correlates with water use under a given set of environmental cond itions (Beeson, 1997; McDermitt, 1990; Teskey & Sheriff, 1996; Vertessy et al., 1995) For individual species, leaf area and cross sectional sapwood area are closely r elated to ETA in balsam fir (Abies balsamea (L.) Mill.) (Coyea & Margolis, 1992) mountain ash (Eucalyptus regnans F.J. Muell.), silver wattle (Acacia dealbata Link.) (Vertessy et al., 1995) and Monterey pine (Pinus radiata D. Don) (Teskey & Sheriff, 1996) 4 Conclusion Daily ETA of Quercus virginiana can be estimated with high precision based on current methods of calculating ETO and using the appropriate coefficients (for PCA or TCSA) for a given measure of tree capacity to move and transpire water, as shown in Figure 3 The three measures using TCSA to estimate water demand (ETA) are suited to nursery production where trunk diameter (caliper) is a ro utine measure for marketing classification, but can be used for isolated landscape trees with due consideration. Extrapolations beyon d live oak tree sizes measured here are possible and would be most accurate if based on trunk cross sectional
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