Estimating ashe juniper leaf area from tree and stem characteristics

Abstract

Ashe juniper (Juniperus ashei Buchh.) is increasing in density and areal coverage on the Edwards Plateau of Texas. This is causing changes in community leaf area that could impact the ecosystem water balance through increased transpiration and interception of precipitation. Our objective was to estimate leaf area of selected trees and shoots in a range of size and age classes using nondestructive methods. We harvested all leaf material from 9 trees ranging in height from 0.8 to 4.8 m and recorded tree height and canopy diameter. We divided each tree into 6 sections based on 3 horizontal strata and 2 vertical hemispheres. Projected leaf area of subsamples, collected from each section, was multiplied by pi to give full cylinder leaf area which was used to calculate specific leaf area (cm2 g-1). Dried leaf biomass for each stratum, hemisphere, and tree was multiplied by the specific leaf area to determine the leaf area. We harvested leaf biomass from shoots and measured in situ stem diameters, dried the leaf biomass, and multiplied it by the specfic leaf area to determine shoot leaf area. There was no significant effect of stratum or hemisphere on specific leaf area or of hemisphere on leaf area. The middle stratum had a significantly greater percentage of total leaf area (52%). Total tree leaf area was best predicted (r2 = 0.97) by canopy area. Shoot leaf area was best predicted (r2 = 0.93) by stem area. Canopy and stem area measurements are rapid, nondestructive means of accurately estimating Ashe juniper tree and shoot leaf area, respectively.