TROPICAL FOREST VEGETATION OF XISHUANGBANNA, SW CHINA AND ITS SECONDARY CHANGES, WITH SPECIAL REFERENCE TO SOME PROBLEMS IN LOCAL NATURE CONSERVATION

The primary forest vegetation and the secondary plant communities in Xishuangbanna, an important region for the conservation of biodiversity in China, are discussed with comments and suggestions for nature conservation. Tropical seasonal rainforest, tropical montane rainforest, monsoon forest on river banks, monsoon forest over limestone and south-subtropical evergreen broad-leaved forest are the main primary forest vegetation types in Xishuangbanna. They demonstrate a diversified species composition and complicated community structure and support many species of economic significance. Due to agricultural exploitation over the last 30 years, primary forests in the areas have been greatly changed. Some have been denuded and some converted into farmlands for rubber plantations or other tropical cash crops, oi for shifting cultivation. As a result secondary vegetation consisting of deciduous monsoon forest, savanna woodland, bamboo Dendrocalamus membranaceus forest, grassland and Chromolaena odoratum community has developed on the abandoned lands on a large scale. The depletion of primary forest by the excessive harvest of useful plants threatens the gene resource. To protect local tropical forests effectively and utilize forest resources rationally, a systematic conservation strategy and more scientific effort are urgently needed. To reduce pressure upon the forests, plantations should be set up for fuel wood and diverse agroforestry systems and multispecies plantations should be introduced and developed.