Abstract
Background: The relationship between biodiversity and ecosystem function has increasingly been debated as the key ecological issues behind ecosystem service provision. Still, many experimental and theoritical based studies have reported inconsistent patterns of biodiversity and ecosystem function relationships, supporting either niche complementarity or selection effect hypothesis. In this study, aboveground carbon (AGC) stock used as a proxy for ecosystem function and examined its relationship with species diversity, through functional diversity and functional dominance. It is hypothesized that (i) diversity influences AGC through functional diversity and functional dominance effects; and (ii) effects of diversity on AGC would be parted for both functional dominance and functional diversity. Community weight mean (CWM) of functional traits (wood density, specific leaf area, and maximum plant height) was calculated to assess functional dominance (selection effects). As for functional diversity (complementarity effects), multi-trait functional diversity (selection effects) indices were computed. The first hypothesis was tested using structural equation modeling. For the second hypothesis, the effects of environmental variables such as slope, aspect and elevation were tested first, and separate linear mixed effects models were fitted afterward for functional diversity, functional dominance, and both.Results: Results revealed that tree aboveground carbon varied significantly along the slope gradient. Species diversity (richness) had a positive relationship with aboveground carbon, even when elevation effects were considered. As predicted, diversity effects on aboveground carbon were mediated through functional diversity and functional dominance, suggesting that both the niche complementarity and the selection effects are not exclusively affecting carbon stock. However, the effects were greater for functional diversity than for functional dominance. Furthermore, functional dominance effects were strongly transmitted by CWM of maximum plant height, reflecting the importance of forest vertical stratification of diversity and carbon relationship. We therefore argue for stronger complementary effects that would be induced also by complementary light use efficiency of tree and species growing in the understory layer.Conclusions: Species diversity (richness) influences carbon stock through functional diversity and functional dominance. Both the niche complementarity and selection hypotheses are important predictors of carbon stock in the study forest.
Modelling mixotrophic functional diversity and implications for ecosystem function