Twig size-number trade-off among woody plants in Tiantong region, Zhejiang Province of China

Abstract

Aims The branch size-number trade-off among woody plants has implications for both the formation of plant architecture and biomass allocation in response to environment stresses.Our objective was to examine how the twig size-number relationship varies among woody plants in subtropical broad-leaved evergreen forests in south-eastern China.Methods The study site is located in Tiantong National Forest Park(29°52' N,121°39' E),Zhejiang Province,in Eastern China.We measured twig length,twig diameter,number of twigs and length and diameter of branches from which the twigs were sampled for 76 woody species in a 1-hm-2 plot.Standardized major axis(SMA) analysis was conducted to examine the quantitative relationship between twig size(cross-sectional area) and the number of twigs at a given twig size(twig intensity).Important findings A significantly negative allometric scaling relationship was found between twig intensity and its cross-sectional area.Under level-Ⅱ light exposure(LE-Ⅱ,40%-80% of the plant under direct light),ever-green species had a much higher twig intensity than deciduous species.However,there was no difference in twig intensity between these two life forms under LE-Ⅰ(40% ehxposure) or LE-Ⅲ(80% exposure).Higher twig intensity was found in evergreen species under LI-Ⅲ than under both LE-Ⅰ and LE-Ⅱ.In contrast,twig intensity of deciduous species was not different among any of the light exposure levels.Shrubs 4 m height had higher twig intensity than sub-trees and trees 4 m at a given twig size.We conclude that the twig size-number trade-off across woody plants in Tiantong was consistent with the Corner's rule(that describes the relationship between twig size and the number of twigs),but might differ among different life forms.Both evergreen species and shrubs are inclined to develop higher twig intensity,which indicates their adaptation to environment stress caused by limitations in light availability.