Differences in pteridophyte diversity between limestone forests and non-limestone forests in the monsoonal tropics of southwestern China
Compared with non-limestone forests, limestone forests tend to show lower pteridophyte diversity, yet they are known to harbor a unique set of species due to their substrate conditions and naturally fragmented habitat areas. Pteridophyte assemblage composition, however, has not been quantitatively investigated in Xishuangbanna, southwestern China, known as one of the most species-rich areas of China. Using a fully standardized sampling protocol, we tested the following hypotheses: (1) pteridophyte species composition is different between limestone forests (LF) and non-limestone forests (NLF); and the differences are attributable to (2) lower species richness in LF; (3) greater spatial and temporal turnovers (beta diversity) in LF; and (4) higher proportion of pteridophyte species restricted to LF. We found significant differences in pteridophyte assemblage compositions between LF and NLF. Average species richness per transect (alpha diversity) was lower in LF than in NLF, but we found no difference in overall species richness (gamma diversity) between LF and NLF at the scale of this study, because species turnover among samples (beta diversity) was higher in LF than in NLF. A total of 23 species were restricted to LF and 32 species restricted to NLF; however, geographic distribution of LF species was limited to certain habitat patches within this habitat. Our results suggest that LF pteridophyte biodiversity cannot be protected by conserving a limited number of habitat patches, because loss of one LF habitat patch may result in local extinction of species or extinction of endemic species that are yet to be discovered.