Effects of habitat fragmentation on the coastal Vatica mangachapoi forest (Dipterocarpaceae) in Shimei Bay, Hainan Island, China

Habitat fragmentation can cause isolation and decline of a formerly continuously distributed population, which leads to loss of genetic variation and increased risk of extinction. Vatica mangachapoi Blanco is a dominant tree species growing in the lowland rainforests of Hainan Island, China. Remarkably, this species dominates a coastal forest in Shimei Bay, Wanning City of Hainan Province (China). Due to logging, expansion of farmland and villages, and construction of tourism facilities, the coastal V . mangachapoi -dominated forest has become fragmented, threatening its future. To evaluate the effects of habitat fragmentation on this unique coastal forest, two V . mangachapoi populations (SM and RY) along the coast and one population in the lowland rainforest near the coast were selected, and their genetic diversity was assessed based on 12 SSR markers. In addition, the genetic structure of the three populations and gene flow among them, and the fine-scale spatial genetic structure (FSGS) of the SM population were also studied. The results show that the three V . mangachapoi populations had comparable levels of genetic variation, and differentiation among them is negligible ( = 0.008 ~ 0.013). Model-based clustering, Principal co-ordinate analysis and the Neighbor-joining (NJ) methods consistently support a homogeneous genetic structure of the three populations, and strong gene flow was detected among them by MIGRATE analyses. Moreover, there is no significant FSGS in the SM population. A relatively short time since habitat fragmentation and gene flow mediated by seed dispersal might be the likely reasons for the high levels of genetic variation and an absence of genetic structure of the coastal V . mangachapoi populations. In conclusion, even though there are no significant effects of fragmentation on the coastal V . mangachapoi forest, strict protection is required to prevent further deforestation and fragmentation. Besides, saplings of V . mangachapoi should be planted in forest gaps to reconnect fragments of the coastal forest, which would be of benefit for the long-term survival of the tropical coastal V . mangachapoi -dominated forest.