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Evidence for "diminishing returns" from the scaling of stem diameter and specific leaf area¹

Department of Plant Biology, Cornell University, Ithaca, New York 14853 USA

ABSTRACT

Research indicates that increases in total leaf area (A_T) may fail to keep pace with increases in total leaf mass (M_L) across plants differing in size (e.g., as measured by stem diameter, D). This "diminishing returns" hypothesis predicts that the scaling exponent for A_T vs. M_L will be less than one and that the exponent for specific leaf mass (i.e., A_T / M_L) vs. D will be negative. These predictions were examined using data from 46 plants ranging between 0.125 cm D 0.485 m across 25 woody dicot species. Standardized major axis slopes were used to quantify scaling exponents and random effects models were used to quantify species and size effects on the numerical values of exponents. The exponents for A_T vs. M_L and A_T / M_L vs. D differed among species and different species groupings. In general, the exponent for A_T vs. M_L was less than one and the exponent for A_T / M_L vs. D was negative, as predicted. However, random effects models indicated that species effects overshadowed size effects, although size effects were statistically significant. The diminishing returns hypothesis therefore receives statistical support, i.e., although the numerical values of exponents are "species-dependent," they are less than unity, as predicted by theory.

Key Words: allometry • functional foliar traits • leaf area • leaf economics • leaf mass • leaf number • random effects models • scaling relationships • specific leaf area

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