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.

Leaf habits (e.g., evergreen or deciduous) can reflect strategies of species adapting to varied environmental conditions. However, how species with different leaf habits coexist within a plant community is still poorly understood. Trait gradient analysis is a new approach to partition plant functional trait variations into alpha (within-community) and beta (among-community) components to quantify the effects of environmental filtering and biotic competition on community assembly. Here, on the basis of establishing forty-eight forest dynamic plots in a subtropical evergreen and deciduous broadleaved mixed forest in central China and measuring of seven functional traits, we compared the trait variation patterns and influencing factors of evergreen and deciduous species by using the trait gradient analysis method. The results showed that there were significant differences between functional traits for evergreen and deciduous species. Alpha trait components consistently varied more widely than beta components. The correlation between species trait mean and the alpha of each trait was highly significant, but there was no significant correlation between beta and alpha trait values. There were relatively weak or nonexistent significant correlations among species mean trait values and alpha trait values of different functional traits. However, the beta trait value showed high and significant correlations in both evergreen and deciduous species. Our results indicated that evergreen and deciduous species adopt similar adaptation strategies (beta component) in the context of environmental change in the community. However, the species initially came to coexist via the ecological positioning of traits (alpha component), which helped reduce competition so individuals could obtain more resources.

The distribution of plant species diversity has long been a major focus on biogeography. Yet, the universality of the popular Rapoport’s rule remains controversial for endemic plants, as previous studies have focused more on broad-ranged species. Here, we collected data for 4418 endemic woody seed plant species across China, including trees, shrubs, and lianas, to explore the latitudinal patterns of species range size and richness, and test the relevant biogeographic law. The species range size distribution was examined for conformity with Rapoport’s rule using four methods (i.e., Steven’s, Pagel’s, the mid-point, and the across-species method). Spatial patterns of species richness along latitudinal gradient were also investigated by parabolic regression. Results showed that species range size increased with latitude for all species as well as by trees, shrubs and lianas, especially assessed by Pagel’s method. Species richness was highest at low latitude, where species range size was smallest, and decreased with increasing latitude. The species range size and richness of shrubs were maximum, followed by trees then lianas. These findings prove that Rapoport’s rule is strongly supported by latitudinal patterns of species distribution in Chinese endemic woody seed plants.