Effects of density dependence in an evergreen-deciduous broadleaf karst forest in southwest China

Abstract There is increasing evidence that density dependence is an important mechanism for the coexistence of species in natural forest communities. Although density dependence among neighbors has been widely studied in tropical, subtropical, and temperate forests, the effects thereof remain poorly understood for non-zonal forest types (e.g., karst forests). Within this context, we conducted a census of tree species (DBH ≥ 1 cm) in a 25 ha plot within the Mulun forest, southwest China. Based on the data collected, a spatial statistical technique was used to detect the prevalence of density dependence after accounting for the effects of habitat heterogeneity. Furthermore, we investigated the relationships between species characteristics and the strength of density dependence. Our results indicate that 19 of the 93 tree species recorded in the species-rich subtropical karst forest showed a decline in strength of clustering from juveniles to adults, as expected from self-thinning, while 61 species exhibited density-dependent effects. The strength of density dependence was closely related to specific species characteristics. Trees with a smaller species abundance and higher aggregation had stronger density dependence. Additionally, the strength of density dependence of evergreen and canopy species was greater than that of deciduous and understory species. Our study demonstrates that density dependence is a prevalent mechanism for regulating population structures of the majority of tree species in forest ecosystems. Our findings further improve the understanding of species coexistence and forest ecosystem stability, and provide guidance for forest management.