Environmental factors related to community-level functional traits in limestone hill forests along an altitudinal gradient: a case study in northern Thailand

This study investigated the environmental factors affecting functional traits, which have been shown to be important for species assembly in diverse forest stands on limestone hills in northern Thailand. We established 54 plots of 400 m2 in three forest sites (lower, middle, and upper) established along an altitudinal gradient on a limestone hill. The functional traits were assessed and then linked to environmental factors governing forest composition. Results indicated that elevation, rocky outcroppings, and sunlight were important factors affecting functional trait diversity at the study site. Areas with high values of these three factors exhibited increased community-level leaf size, specific leaf area, and leaf thickness, all of which are associated with light-demanding species. However, in areas with low values of these three factors, we observed increased community-level wood density and maximum plant height, which are characteristic of shade-tolerant species. Elevation also positively affected functional dispersion and functional richness values, indicating a wide functional trait space in higher elevation areas, but lower areas exhibited a narrower functional trait space. We suggest that combining a trait-based approach with environmental factors can reveal patterns of species composition in limestone forests.