Leaf area index and site water balance of loblolly pine ( Pinus taeda L.) across a precipitation gradient in East Texas

Abstract

Leaf area index (LAI, m 2 m −2) and site water balance were measured in closed-canopy loblolly pine ( Pinus taeda L.) plantations in East Texas. LAI was measured using littertrap collections and the LI-COR LAI-2000 Plant Canopy Analyzer (PCA) and site water balance was determined using a model developed by Thornthwaite and Mather [Thornthwaite, C.W., Mather, J.R., 1957. The water balance. Publications in Climatol. Vol. 8, pp. 1–104.]. The site water balance model uses precipitation, temperature and soil texture and moisture holding capacity to determine the balance of moisture inputs and outputs. The relationship between loblolly pine LAI and soil moisture availability indices (actual evapotranspiration and moisture deficit) was analyzed across a naturally occurring 50-cm precipitation gradient in East Texas. Results indicated no significant relationship between LAI using the PCA estimates and actual evapotranspiration ( r 2=0.062) or moisture deficit ( r 2=0.057). The lack of correlation was attributed to the deviation from historical precipitation patterns during the years just prior to sampling, which largely eliminated the precipitation gradient during the sampling period. One interesting result was the significant relationship found between LAI and nutrient content of the pine foliage. Although no correlation was found with PCA-based LAI, a significant correlation was found between littertrap LAI estimates and foliar concentrations of nitrogen and phosphorus ( r 2=0.863 and 0.873, respectively), suggesting that, given the recent precipitation patterns, site fertility may be a stronger determinant of stand LAI than water availability.