Plant height–crown radius and canopy coverage–density relationships determine above-ground biomass–density relationship in stressful environments

Abstract

Debate continues in theoretical ecology over whether and why the scaling exponent of biomass–density ( M – N ) relationship varies along environmental gradients. By developing a novel geometric model with assumptions of allometric growth at the individual level and open canopy at the stand level, we propose that plant height–crown radius and canopy coverage–density relationships determine the above-ground M – N relationship in stressful environments. Results from field investigation along an aridity gradient (from eastern to western China) confirmed our model prediction and showed that the above-ground M – N scaling exponent increased with drought stress. Therefore, the ‘universal’ scaling exponents (−3/2 or −4/3) of the M – N relationship predicted by previous models may not hold for above-ground parts in stressful environments.