Trees species' dispersal mode and habitat heterogeneity shape negative density dependence in a temperate forest

Conspecific negative density dependence (CNDD) is a potentially important mechanism in maintaining species diversity. While previous evidence showed habitat heterogeneity and species' dispersal modes affect the strength of CNDD at early life stages of trees (e.g., seedlings), it remains unclear how they affect the strength of CNDD at later life stages. We examined the degree of spatial aggregation between saplings and trees for species dispersed by wind and gravity in four topographic habitats within a 25-ha temperate forest dynamic plot in the Qinling Mountains of central China. We used the replicated spatial point pattern (RSPP) analysis and bivariate pair correlation function (PCF) to detect the spatial distribution of saplings around trees at two scales, 15 and 50 m, respectively. Although the signal was not apparent across the whole study region (or 25-ha), it is distinct on isolated areas with specific characteristics, suggesting that these characteristics could be important factors in CNDD. Further, we found that the gravity-dispersed tree species experienced CNDD across habitats, while for wind-dispersed species CNDD was found in gully, terrace and low-ridge habitats. Our study suggests that neglecting the habitat heterogeneity and dispersal mode can distort the signal of CNDD and community assembly in temperate forests.