Ecological uniqueness of species assemblages and their determinants in forest communities

Aim Beta diversity can be partitioned into the contributions of individual sampling units to overall beta diversity, which are comparative indicators of the ecological uniqueness of species assemblages in the sampling units. Yet, what determines ecological uniqueness has rarely been examined. Here, we investigated the determinants of ecological uniqueness in species assemblages in forest communities. Location China. Methods We used tree census data, combined with spatially explicit environmental variables collected from forest dynamics plots across tropical, subtropical and temperate forests in China. We computed beta diversity as the total variation of the community data, and a site-based approach was used to determine whether ecological uniqueness is related to local environmental conditions and/or community characteristics. Results Ecological uniqueness was explained by both local environment and community characteristics, but their relative importance varied across the four forest types. We provide direct evidence that the relationship between ecological uniqueness and species richness (EUSRR) is related to the percentage of rare species in the community. Local environmental factors affecting ecological uniqueness and beta diversity were inconsistent, indicating that focusing simultaneously on beta diversity and ecological uniqueness with regard to local environmental conditions is likely to be the appropriate approach to study forest community assembly. Main conclusions Although the EUSRR was negative in some cases, indicating high species richness, this does not necessarily imply high ecological uniqueness. Thus, for biological conservation, species-rich sites and unique low-richness sites should be valued more. The higher degree of ecological uniqueness indicates unique species compositions, which provides insight into finding such quadrats and taking measures for protection, restoration or management. We propose that focusing simultaneously on the beta diversity, species richness and ecological uniqueness of individual quadrats is likely to be a valuable approach for biodiversity conservation programmes.

Automated summary

The study investigated the determinants of ecological uniqueness in species assemblages in forest communities in China. It was found that ecological uniqueness is influenced by both local environment and community characteristics, and that the relationship between ecological uniqueness and species richness is related to the percentage of rare species in the community. Therefore, simultaneously focusing on beta diversity and ecological uniqueness with regard to local environmental conditions is recommended for studying forest community assembly and biodiversity conservation.