Phytogeography and Floristic Affinities of the Limestone Flora of Mt. Exianling, Hainan Island, China

The limestone forest of Mt. Exianling on Hainan Island, China, was inventoried, and their floristic composition and biogeographical affinities discussed. Botanical surveys recorded 1121 vascular plant species belonging to 620 genera and 171 families; of which 81 represented significant records including 11 new species. Mt. Exianling is characterized by phanerophytes making up ca. 79% of the total flora, and those with mesophyllous leaves comprising ca. 64%. Ecological species groups were discerned from field observations: species exclusive to limestone habitats make up 2.4% of the total flora. Based on their distributions, 11 biogeographic elements at the generic level are recognized. Our work on Mt. Exianling revealed closer affinity to tropical Asian floras than to temperate elements of eastern Asian floras, with ca. 90% of the seed plant genera being tropical; this limestone forest is essentially tropical and is part of the tropical Asian flora at its northern margin. Unfortunately, Exianling has been subject to environmental threats from mining activities in the past two decades. Kadoorie Conservation China has heavily involved in the conservation of Exianling limestone forest and partially financed the above floristic studies. A nature reserve station was constructed in 2009, and now Exianling is being gazetted as a formal provincial nature reserve. Recently, activities in exploiting of the gold mining in Exianling has been stopped by the nature reserve.