Figure 1. Permanent plot locations in the natural D. pectinatum communities in the three national nature reserves of Bawangling, Diaoluoshan and Jianfengling, Hainan Island, China.
Hainan Island is located at the northern edge of tropical Asia. The topography is higher in the middle than around the edges of the island. The average annual precipitation decreases from east to west, and the annual average temperature decreases from south to north. The southwest and west are affected by the ocean monsoon, and there are obvious wet and dry seasons. More clouds and lower temperatures occur in the central mountainous region than elsewhere on the island. The study was conducted along three environmental axes (i.e., precipitation and temperature gradients) in Bawangling, which is located in the southwestern part of Hainan Island (18°53′-19°20′N, 108°58′-109°53′E), Diaoluoshan, which is situated in the southeastern part of Hainan Island (18°43′-18°58′N, 109°43′-110°03′E), and Jianfengling, which is located in the southwestern part of Hainan Island (18°23′-18°50′ N, 108°36′-109°05′E). These areas are national nature reserves in China.
The total area of the Bawangling Nature Reserve is approximately 72,000 hm2. It has a tropical monsoon climate, the annual mean temperature is 23.6 °C, and the annual mean precipitation is between 1500 and 2000 mm. The total area of the Diaoluoshan Nature Reserve is approximately 37,900 hm2. It has a marine tropical monsoon climate. The annual mean temperature is 24.4 °C, and the annual mean precipitation is between 1870 mm and 2760 mm. The total area of the Jianfengling Nature Reserve is approximately 640 km2, and it has a monsoon climate typical of tropical islands at low latitudes. The annual mean temperature is between 19.7 °C and 25.2 °C, and the annual precipitation is between 1600 mm and 2600 mm.
The tropical mountain forests at the three sites are mainly distributed on mountaintops at elevations above 800 m, and they are among the few well-preserved forest types with tropical rainforest properties in China. They constitute the northern boundary of the Southeast Asian tropical rainforests and represent a forest type that transitions from tropical rainforest to subtropical/warm temperate rainforest (Ding et al. 2012). This unique setting also allows these forests to play an irreplaceable role in research on tropical and subtropical rainforest ecology (Fang et al. 2004). They could also provide an ideal place to explore the natural regeneration dynamics of tropical forests. Hence, a total of sixty-eight permanent plots in the natural D. pectinatum communities were investigated, and the sampling information for the three sites is provided in Figure 1. Based on field investigations, detailed coordinate, climate (data from WorldClim-Global Climate Data (http://www.worldclim.org/ )) and topography data for the three sites are shown in Table 1.
Table 1. Topographic and climatic characteristics across the three study sites