<S3-1> Carbon allocation of tropical rainforest in Lambir, Borneo

Abstract

It is important to understand the characteristics of carbon cycling in tropical rainforests in order to quantify global carbon cycling. Knowledge about carbon allocation, that is, how much of the carbon assimilated by photosynthesis is allocated to aboveground and belowground tissues, and how much is used for biomass production and respiration on an annual time scale and on an ecosystem scale, can improve our ability to predict the effects of global climate changes on carbon dynamics. Recently, studies on carbon allocation in the Neotropics have been increasing, while there are few such studies in Asian tropical rainforests. There are important biotic and abiotic differences between the tropical rainforests in Borneo and Neotropical rainforests, such as higher stand density of large trees, larger biomass, and absence of distinct dry seasons in the rainforests in Borneo. These factors may cause differences in the carbon allocation patterns between Borneo and the Neotropics. The goal of this study is to clarify characteristics of carbon allocation in Lambir Hills National Park, which is covered with typical Bornean mature tropical rainforests. We estimated above-ground net primary production (ANPP), woody tissue respiration (Rwood), foliage respiration (Rfoliage), total below-ground carbon flux (TBCF) and gross primary production (GPP) in the Lambir Hills tropical rainforest, and compared the values with those from Neotropical tropical rainforests. We found that the aboveground biomass (AGB) in the Lambir Hills tropical rainforest was approximately twice higher than that in Neotropical rainforests. ANPP, Rwood and Rfoliage were comparable despite the higher biomass. The comparable Rwood despite higher aboveground biomass was partly caused by higher stand density of large trees in the Lambir Hills tropical rainforest. TBCF in the Lambir Hills tropical rainforest was much higher than those of Neotropical forests. This was unexpected, since the higher water availability in the Bornean tropical rainforest would suggest less fine root competition for water, giving higher ANPP and lower TBCF. Low nutrient availability may explain the comparable ANPP and higher TBCF. Our results suggested that large trees and belowground resources considerably affected carbon cycling.