Allometric models for the estimation of foliage area and biomass from stem metrics in black locust

Abstract

Allometric equations relating trees’ vascular system and other stem metrics with foliage area and mass are important to estimate their growth, carbon stocks and interactions with abiotic environment in terms of carbon and water balance. In this study we focused on Robinia pseudoacacia restoration plantations in Greece and aimed at establishing species-specific models to predict foliage leaf area and biomass based on stem traits. In particular, we evaluated stem cross-sectional areas of sapwood, current sapwood and total stem (sap-wood and heartwood), measured at different tree heights, as predictors of leaf area and mass, based on the pipe model theory. Furthermore, we assessed the variation in the ratios of leaf area to different stem cross-sectional areas across the tree profile and we examined the relationships of diameter at breast height (DBH) with diameter at the base of the live crown and with leaf area. Taking into account the trees’ DBH distribution according to the planta-tions’ inventory, 25 black locust individuals were destructively sampled and the relationships among the studied traits were analyzed by means of multiple and simple linear regression at p<0.001. Foliage dry mass and area were best predicted by total stem cross-sectional area at mid-bole and stump height (R 2 =0.81), followed by current sapwood area at stump height (R 2 =0.74), which outperformed the most often used sapwood area (R 2 =0.70). DBH was also reliably estimating tree leaf area (R 2 =0.72) but was less precise, compared to total cross-sectional area, while it was a useful proxy of diameter at the base of the live crown (R 2 =0.80). In line with the pipe model theory, the ratio of leaf area to total cross-sectional area declined across the canopy basipetally, but only when total cross-sectional area was considered. Deviations from the sap-wood-foliage functions described by the pipe model theory may be due to the small sample size and the variability in tree size in such developing restoration plantations. The produced species-specific relationships between stem and foliage metrics may be a useful tool to predict the carbon sequestration and climate change adaptation potential of black locust restoration plantations, which are often characterized by harsh site conditions.