Abstract: Tongguling National Nature Reserve is located in northeastern Hainan Province. To analyze its vegetation variation after 18 years of protection, we investigated the species diversity of plants in the reserve in 2005. A total of 984 plant species, belonging to 618 genera and 166 families, were recorded. Of these, 35 species are endemic to Hainan, such as Cycas hainanensis, Phoebe hainanensis, and Arcangelisia gusanhung, and 12 are listed as nationally endangered and protected species, including Cibotium barometz, Cycas hainanensis, Oncodostigma hainanense, Aquilaria sinensis, Hydnocarpus hainanensis, Homalium hainanense, Ixonanthes chinensis, Antirhea chinensis, Dimocarpus longan, Litchi chinensis, Gmelina hainanensis, and Artocarpus hypargyreus. The Shannon-Wiener indices of the three major vegetation types, namely tropical evergreen monsoon elfin forest, tropical shrubland, and mangrove forest, were 4.7485, 4.5876, and 1.8096, respectively, while Simpson diversity indices were 0.9247, 0.9206, and 0.6978, respectively. In the 2,800-m2 plots of tropical evergreen monsoon elfin forest, a total of 1,366 trees over 1.5 m tall were recorded, belonging to 81 species. Of these, the top five dominant species were Litsea variabilis, Hydnocarpus hainanensis, Arytera littoralis, Bridelia insulana, and Sapindus mukorossi. It is notable that the dominant species Schefflera octophylla in 1987 has been replaced by Litsea variabilis. Among the trees more than 1.5 m tall in the 3,300-m2 plots, there are 20 singleton species and 13 doubleton ones, accounting for 32.7% of the total tree species. In general, the development of tropical evergreen monsoon elfin forest tends to be stable, and shrublands are in succession to secondary forests. The area of mangrove forests has been reduced because of serious destruction. Therefore, further protection of Tongguling National Nature Reserve is important and necessary.

Key words: quillwort, endangered plant, natural distribution and status, conservation