Abstract
Aims
The factors affecting species abundance are a subject of ongoing debates in community ecology. Empirical studies have demonstrated that tree abundance is affected by plant functional traits and negative density dependence (NDD). However, few studies have focused on the combined effects of negative density dependence and plant functional traits on species abundance.
Methods
In this study, we used tree functional traits and two census data from a 50-ha forest dynamic plot in the Heishiding (HSD) Nature Reserve to explore the combined effects of functional traits and NDD on species abundance. Using hierarchical Bayesian models, we analyzed how neighbor densities affected the survival of saplings from 130 species and extracted posterior means of the coefficients to represent NDD. The structural equation modeling (SEM) analysis was then applied to investigate the causal relationships among species functional traits, negative density dependence, and species abundance.
Important findings
SEM showed that tree functional traits, including specific leaf area (SLA), leaf area (LA), leaf dry matter content (LDMC), leaf N content (LNC), maximum electron transport rate (ETRmax), and conspecific adult negative density dependence (CNDDadult), together explained 20% of the total variation in tree abundance. Specifically, SLA affected tree abundance both directly and indirectly via CNDDadult, with a totally negative influence on abundance. LDMC and LNC had only indirect effects mediated by CNDDadult on tree abundance. ETRmax and LA had directly negative effects on abundance, but their direct connections with CNDDadult were not observed. In addition, CNDDadult was negatively correlated with species abundance, indicating that abundant species are under stronger negative density dependence. Among these investigated traits, SLA contributed the most to the variation in CNDDadult and abundance. We argued that our findings of trait-CNDDadult-abundance relationships can improve our understanding of the determinants of species commonness and rarity in forests.