Density-dependent selection effect of dominant species rather than species diversity increased aboveground biomass accumulation in a temperate oak forest

Abstract

Forest aboveground biomass (AGB) exerts a critical role in mediating the global carbon cycle. The impacts of multiple abiotic and biotic factors on AGB have been extensively discussed, research on artificially assembled ecosystems has consistently shown that AGB is predominantly influenced by the prevalence of dominant species. However, it is unclear whether forest AGB is also regulated by the varying proportions of dominant species within a community. Based on nine relative density gradients (10 % - 90 %) of Quercus aliena var. acutiserrata populations, this study explored the spatial pattern in forest AGB and the underpinning drivers using generalized linear mixed models (GLMM) and structural equation modeling (SEM). Our results showed that as relative density of the dominant oak species increases, the community AGB, soil nutrients, intraspecific competition intensity and evolution diversity significantly increased, whereas tree species diversity, intraspecific and interspecific diameter at breast height (DBH) variation and interspecific competition intensity all significantly decreased. Soil nutrients could exert an important positive effect on forest AGB accumulation by mediating tree species diversity (Simpson index) and interspecific exclusion stress (interspecific DBH variation and competition intensity). Species diversity and interspecific DBH variation had negative impact whereas the interspecific competition intensity exerted positive contribution on forest AGB. We found that the density-dependent selection effect may be the fundamental cause of biodiversity loss and aboveground biomass accumulation, which highlights the significant influence of dominant species density on community development. Our study provides a valuable insight into the crucial role of dominant species populations in regional forest carbon sinks predication and forest ecosystem management.