Wood density is a sustainability indicator for the management of dry zone homegarden agroforests: Evidences from biodiversity-ecosystem function relationships

摘要

Recent studies have advanced our understanding regarding the niche complementarity and mass ratio effects on the ecosystem function, in both natural and experimental systems. However, biodiversity-ecosystem function (BEF) relationships may be fundamentally different across dense-wooded and light-wooded species, as they are clustered at two opposite extremes of the wood economics spectrum. Here we analyzed BEF relationships through mediations of functional dominance (i.e. community-weighted mean, CWM) and functional divergence (FDvar) of plant maximum height (H) while accounting for the effects of other characteristics of homegardens, across dense-wooded, light-wooded and all species, by using structural equation modelling (SEM) on 45 homegarden agroforestry systems in the dry zone of Sri Lanka. The dense-wooded SEM accounted for 69% variation in aboveground biomass through significant positive direct effects of CWM H (beta = 0.51) and FDvar H (beta = 0.20), and indirect effect of species diversity via FDvar H on aboveground biomass (beta = 0.12). Although the light-wooded SEM accounted for 19% variation in aboveground biomass, the BEF relationships were non-significant. Regardless of SEMs, FDvar H but not CWM H was significantly positively related to species diversity. None of the BEF relationships was statistically significant when dense-wooded and light-wooded species were mixed. From a theoretical aspect, these positive BEF relationships are driven by both dominant and complementarity dense-wooded species. From a practical aspect, the positive BEF relationships support the feasibility of UN Reducing Emissions from Deforestation and Forest Degradation (REDD +) initiative in studied agroforests, which aims to enhance carbon storage in aboveground biomass while conserving biodiversity. Hence, this study suggests that wood density is a potential sustainability indicator for better management of agroforest-ecosystem while driving positive BEF relationships.