Spatial patterns and drivers of plant diversity in the tropical city of Sanya, China

Drivers of patterns in plant diversity remain poorly understood in tropical cities. Therefore, we investigated diversity within the tropical city of Sanya in Hainan Province of southern China by sampling one to three plots within 154 urban functional units (UFUs) based on six primary and 18 secondary UFUs. To measure diversity, we determined the number of vascular plants (species richness; SR) within each functional unit based on vegetation plots. We computed Faith's phylogenetic diversity (PD_Faith) using a large megatree of plant life. To assess the potential drivers of SR and PD_Faith we performed multiple regressions using socioeconomic, biophysical, and vegetation management variables. The results showed significant differences in SR and PD_Faith among the six primary UFUs. PD_Faith of cultivated species was significantly higher than PD_Faith of spontaneous species in all UFUs except in the wasteland area. Management measures were better predictors of SR and PD_Faith than socioeconomic variables. The best predictor of SR and PD_Faith of spontaneous species was the management of the urban green space. Our results provide clear guidelines for improved management strategies in Sanya, especially by showing how spontaneous and/or cultivated plant diversity can be encouraged depending on environmental, ecological, and cultural needs. Our work also adds to the presently scarce literature on drivers of urban plant diversity in tropical cities worldwide.