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Determination of leaf area index of loblolly pine (Pinus taeda L.) and its relationship to site water balance across a large precipitation gradient in East Texas
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The relationship between leaf area index (LAI) and site water balance (SWB) in closed canopy lobiolly pine plantations was analyzed across a natural 50-cm precipitation gradient in East Texas. Six precipitation zones were delineated based upon historical weather data, and 60 stands (10 per zone) were randomly chosen for study. LAI was estimated using three techniques: a diameter-based allometric equation, the LiCor LAI-2000 Plant Canopy Analyzer (PCA), and standard 1 M2 litter traps. SWB was estimated using the Thornthwaite and Mather (1957) model to predict potential and actual evapotranspiration and moisture deficit. LAI and site water balance were estimated in both 1994 and 1995. 1 hypothesized that LAI would be positively correlated with actual evapotranspiration (AET) and negatively correlated with moisture deficit for the 60 stands. Results, however, indicate no significant relationship between LAI and AET (@=0.062) or moisture deficit (r-'=O.057). The lack of correlation was attributed to the deviation from historical precipitation patterns during the-last four years which largely eliminated the precipitation gradient among zones during the sampling period. One interesting result was the significant correlation between litter trap LAI estimates and foliar nutrient concentrations of nitrogen and phosphorus (@=0.863 and 0.873 respectively); this suggests that, given the recent precipitation patterns, site fertility may be a stronger determinant of stand LAI than water availability. The estimates of LAI (M2M-2 ) ranged from 0.41 to 4.64 as determined by the PCA, from 0.55 to 3.31 from the allometric equation, and from 3.68 to 5.54 from liftertrap data. Although no significant relationships could be drawn between LAI estimates and outputs of the SWB model, the PCA did show the ability to rank stands by the amount of leaf area present in the canopy and detect seasonal changes in LAI unlike the allometric equation. The absolute LAI values given by the PCA were not precise, but the PCA could determine relative changes in LAI, either seasonal or among stands.
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Includes bibliographical references: p. 39-42.
Issued also on microfiche from Lange Micrographics.
Hebert, Mark Thomas (1996). Determination of leaf area index of loblolly pine (Pinus taeda L.) and its relationship to site water balance across a large precipitation gradient in East Texas. Master's thesis, Texas A&M University. Available electronically from
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