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 vs. 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 vs. M_max) and constrained to be ≤ -1.0.

We tested this hypothesis by analyzing the twigs of 123 species datasets complied 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 -a (-1.19) was not statistically different from the exponents of M_min vs. 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 vs. the leafing intensity based on stem volume (LIV). In the case of M_min and M_max vs. 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 maybe closely correlate with M_min vs. M_max. Besides, constrained by the maximum leaf mass expand, the broad scope range between leaf size and number may be insensitive to leaf habit groups in subtropical mountain forest.

A total of 68 and 75 species were sampled from the two sites (Table 1). The total number of sampled species was 123 (including 20 overlapping species) belonging to 92 genera of 53 families. In August 2016 and 2017, three to five current-year undamaged, healthy twigs from three individuals of each species were randomly selected. All of the leaves (with petioles) on each twig were removed and counted (N_L). Twig diameter (D) and length (L) were measured using a vernier caliper, with an accuracy of 0.1 mm (Milla, 2009). The stem volume of each twig (V_stem, mm³) was estimated using L and D assuming stems are cylindrical. Stems and leaves were brought to the laboratory where they were oven-dried at 75 ºC to determine total leaf mass (M_leaf) and stem mass (M_stem). Each leaf of each twig was subsequently scanned and its area was calculated using the Image J software (Image J 1.2v; National Institutes of Health, USA). Then, we multiplied the area of the largest and smallest leaf per twig by leaf mass per area (LMA, total leaf mass divided by total leaf area) to estimate the maximum and minimum leaf mass per twig, respectively. The volume-based leafing intensity (LIV) is here defined as N_L / V_stem; the mass-based leafing intensity (LIM) is here defined as N_L / M_stem.

This dataset contains the leaf traits of 123 woody species.