Comparison of calculated and measured leaf masses of urban trees

Accurate leaf-mass determination is a critical factor in estimating the mag nitude of biogenic hydrocarbon (BHC) emissions from green plants. In severa l past studies that developed BHC emissions estimates for urban areas, a vo lumetric approach was used to estimate leaf masses of urban trees. Crown vo lumes were modeled by geometric solids and then multiplied by species-speci fic leaf-mass constants (experimentally determined leaf mass-to-volume rati os) to obtain leaf mass, although associated uncertainties were not well ch aracterized. The purpose of the present study was to examine the precision and accuracy of a volumetric approach using geometric solids to compare est imated leaf masses to measured whole-tree leaf masses, and to compare leaf- mass constants derived from selective sampling within crowns to whole-tree values. Accordingly, total leaf masses obtained through tree harvest and le af removal of 21 urban trees were compared to leaf masses calculated using geometric solids to model the shapes of tree crowns and leaf-mass constants found in the literature. Leaf masses were also calculated from recently pu blished allometric equations. Using the experimentally measured total leaf mass and dimensions of each tree, whole-tree leaf-mass constants were also calculated. Results from this study suggest that leaf-mass estimates develo ped for individual trees through a volumetric approach may be within simila r to 50% of actual values. For the 21 trees in this study, sums of leaf-mas s estimates were within similar to 20% of the sum of the measured leaf mass es when the vertical ellipsoid, sphere, or preferred solids were used. Leaf masses per unit area of crown projection for these urban trees were greate r than the values of leaf mass per ground surface area reported for eastern deciduous forests.