ObjectiveThe driving factors of plant diversity differences among three cities in Hainan Province, southern China were discussed through the analysis of plant compositions. It provided a reference for future research on the protection and layout of urban plant diversity.

MethodIn this research, Haikou City, Wenchang City and Sanya City were taken as research objects. A sample survey was conducted using random sampling in urban planning areas. We carried out surveys on the species list within the plot, the DBH, crown width, height and quantity of trees, as well as the vegetation coverage area in the plot, etc. The β-dissimilarity index was used to study the compositional differences of communities and species in different cities. We analyzed the differences in plant species diversity at the species, function, and phylogenetic levels, and factors which may influence urban plant diversity differences.

Result(1) In the planning area of Haikou City, there were 227 plant species of 184 genera in 71 families. In the planning area of Sanya City, there were 244 plant species of 204 genera in 76 families. In the planning area of Wenchang City, there were 230 plant species of 181 genera in 72 families. (2) In the three cities, the β-dissimilarity index of the native species was higher than that of the exotic species, and the species β-dissimilarity of the arbor layer was lower than that of the shrub layer and the herb layer. (3) There was no significant difference in species diversity index values of the arbor layer. Diversity index value of shrub species in Wenchang City was significantly lower than those in Haikou and Sanya cities (P < 0.05). The herb layer diversity index values of Sanya and Wenchang showed significant differences (P < 0.05), and Wenchang’s diversity index value was higher. (4) The functional evenness index (FEve) and the functional dispersion index (FDis) of the shrub layer were significantly different, which were reflected between Wenchang City and the other two cities (P < 0.01 and P < 0.001, respectively). The diversity index value of Wenchang City was lower than that of Haikou and Sanya cities, which was consistent with the species diversity of the shrub layer. (5) The pedigree phylogenetic index (PD) of Wenchang City arbor layer was significantly higher than that of Haikou City (P < 0.01). The PD index of Sanya City shrub layer was significantly higher than that of Wenchang City. The PD index of Wenchang City herb layer was significantly higher than that of Haikou and Sanya cities (P < 0.01). The phylogenetic species evenness (PSE) results for the shrub and herb layers were consistent with the PD index (P < 0.001 and P < 0.01, respectively), but did not show significant differences in the arbor layer (P = 0.690).

ConclusionThe vegetation types of the three cities in Hainan Province did not exhibit obvious homogeneity, while the differences in native species composition were more pronounced than those of exotic species. Species diversity, functional diversity and phylogenetic diversity levels in the three cities basically showed the same trend. In future studies, the analysis of plant diversity from multiple layers in cities could provide a more comprehensive decision-making basis for both the protection and the control of diversity patterns.