How does light availability affect the aboveground biomass allocation and leaf morphology of saplings in temperate mixed deciduous forests?

Abstract

Light is the most important physical variable that affects patterns of biomass allocation. A quantitative understanding of biomass allocation patterns is crucial to quantifying ecosystem dynamics and might have many practical uses in silviculture. In this research, we investigated the allocation of the aboveground biomass to leaves, branches, and bole as well as leaf morphology, using 26 saplings of Alnus subcordata C. A. M., 26 of Carpinus betulus L., and 27 of Fagus orientalis L. within a wide gradient of light conditions. Saplings were harvested in August 2014 in temperate, mixed deciduous forests of northern Iran in three sites with similar topographic conditions. A linear mixed effect model was used to evaluate the effect of light and species. Moreover, we developed biomass allometric equations using nonlinear seemingly unrelated regression. Biomass allocation to different organs and all leaf morphological traits were different among species. Light affected biomass allocation to leaves as well as specific leaf area and the direction of the effect was different for each species. Branch and bole allocation, leaf area ratio, and leaf area index were not affected by light. The effect of the interaction between light and species was significant for leaf allocation, branch allocation and specific leaf area. Moreover, sapling size seems to be an important factor explaining the effect of light on biomass allocation. Deriving highly precise biomass equations was possible by just using diameter at breast height and height, and available light did not improve the precision of models.