Abstract
Understanding the scaling between leaf size and leafing intensity (leaf number per stem size) is crucial for comprehending theories about the leaf costs and benefits in the leaf size-twig size spectrum. However, the scaling scope of leaf size versus leafing intensity changes along the twig leaf size variation in different leaf habit species remains elusive. Here, we hypothesize that the numerical value of scaling exponent for leaf mass versus leafing intensity in twig is governed by the minimum leaf mass versus maximum leaf mass (M (min) versus M (max)) and constrained to be ≤-1.0. We tested this hypothesis by analyzing the twigs of 123 species datasets compiled in the subtropical mountain forest. The standardized major axis regression (SMA) analyses showed the M (min) scaled as the 1.19 power of M (max) and the -α (-1.19) were not statistically different from the exponents of M (min) versus leafing intensity in whole data. Across leaf habit groups, the M (max) scaled negatively and isometrically with respect to leafing intensity. The pooled data's scaling exponents ranged from -1.14 to -0.96 for M (min) and M (max) versus the leafing intensity based on stem volume (LIV). In the case of M (min) and M (max) versus the leafing intensity based on stem mass (LIM), the scaling exponents ranged from -1.24 to -1.04. Our hypothesis successfully predicts that the scaling relationship between leaf mass and leafing intensity is constrained to be ≤-1.0. More importantly, the lower limit to scaling of leaf mass and leafing intensity may be closely correlated with M (min) versus M (max). Besides, constrained by the maximum leaf mass expansion, the broad scope range between leaf size and number may be insensitive to leaf habit groups in subtropical mountain forest.