Tree abundance, richness, and phylogenetic diversity along an elevation gradient in the tropical forest of Diaoluo Mountain in Hainan, China.

Taxonomic and phylogenetic diversity within forest communities are influenced by many factors, but our understanding concerning diversity patterns along elevational gradients is still unclear. Though there are many studies on diversity patterns such as phylogenetic diversity (PD), there are only handful describing how altitude affects these diversity patterns, especially in the tropical forest areas of China. It has been assumed that increases in elevation can lead to gradual decreases in abundance, richness, and phylogenetic diversity. Here, we assessed these parameters in fifteen 50 × 50 m plots across various elevations (281 m–1175 m) at Diaoluo Mountain of the Hainan tropical forest in the years 2010 and 2015. Regressions between tree richness, PD, and environmental variables (climate and soil variables) were conducted to uncover the potential drivers of tree richness and PD. We found that the tree abundance, richness, and phylogenetic diversity first increased with increasing elevation, then reached maximum values at intermediate elevations, and finally decreased at the highest elevations. Tree species composition was mainly shaped by elevation (p = 0.001 < 0.005), suggesting that intermediate elevations result in an environmental screening effect due to the abundance of energy and moisture resources (i.e., high temperature and humidity), which is typical of tropical forests. We speculate that the intermediate elevations and historical disturbances shape the available species pool. Overall, our research revealed the diversity patterns of the Diaolu Mountain plants along the elevation, providing the basis for future plant protection planning, such as protecting plant species, maintaining plant habitats, and coordinating plant management in the area. • Handful studies describing how altitude affects diversity patterns in the tropical forest areas of China • Tree abundance, richness, and phylogenetic diversity were assessed across various elevations at Diaoluo tropical forest. • Tree abundance, richness and phylogenetic diversity increased at first and then decrease with increasing elevation. • The diversity pattern of the Diaoluo Mountain plants provides the basis for future plant protection planning. [ABSTRACT FROM AUTHOR]