| Guangxi, an integral part of the fragile southwest Karst ecosystems, and is typical of the subtropical karst region in the world. In this paper,the north tropic Karst forest Nonggang Nature Reserve in Long Zhou county of southwest Guangxi and karst plate of Guilin in north-east of Guangxi were selected as investigation,and based on the data collected from 13 plots, applying methods of quantitative ecology, population ecology and plant communities for a more systematic study to the perspective of vegetation stability and habitat fragmentation in karst of Guangxi. It is designed to provide a scientific theory for vegetation recovery and reconstruction works of degraded ecosystems in karst areas.(â…°) Pilot study was show that the effects on vegetation of habitat fragmentation in karst area dominate by monadnock and isolated peak. But in bigger patch such as Nonggang Nature Reserve, the patch size is irrelevant with vegetation stability. The difference of Nonggang Nature Reserve mainly existed in which are due to the diversity of karst geology, water and heat conditions, bareness degree of rock, soil-forming conditions and vegetation type. The age structure shows the dominate specie Cyclobalanopsis glauca in karst plate of Guilin which has a serious habitat fragmentation has a poor population stability while thediameter structures of the dominant species in Nonggang Nature Reserve show a Pyramid style. These show that the age stucture of plant population in nature reserve which has a lower habitat fragmentation degree is reasonable and stable. Anymore, the age structure of the Cyclobalanopsis glauca population in karst plate of Guilin show a Pyramid style obviously only in one site, futhermore, the plant community in the site is the biggest isolated peak plant community in all my vestigations, so the plant population has stonger capcity for maintaining stability in big patch.(â…±) In karst plate of Guilin, habitat fragmentation serious, the community of biological diversity higher than Nonggang Nature Reserve which lower level of fragmentation. The edge effect in broken habitat increase biodiversity. High biodiversity community does not have a high stability, in the circumstances of habitat fragmentation, on the contrary, the community of high biodiversity, but poor stability. Landscape fragmentation leading to a high degree of heterogeneity of habitat, adapt to different habitats for the species to provide niche space, to a certain extent, promote the differentiation of species niche, but all species of ecological sites may be small, once subject to interference is very likely to lose their niche; Lane Nature Reserve and the original vegetation after a long-term evolution, the competition between species and synergies have been very stable, with the species occupy their own niche, with a wide range of ecological stability and the rate of other invasive species to occupy within the community Eco-space, thus the relative biodiversity lower.(â…²)It show that habitat fragmentation has a great influence on vegetation biomass, the biomass of tree in karst plate of Guilin are less than Nonggang Nature Reserve. But plant biomass has a directive relationship with vegetation structure, such as big window of woods. The results of LAI index show that, the tree LAI indexes of 7 plots in Guilin sites are lower than Nonggang Nature Reserve,too. Light utilization rate of tree is low in fragmental habitats. Additionally, I provide a low correlation coefficient of 0.332 between the fragmental area and tree LAI. The result suggest that the fragmental area might not directly affect the tree layer. But the correlation coefficient between the fragmental area and total LAI (tree and shrub) is 0.667, this suggest that fragmentation has some influence on the light utilization of vegetation.(â…³) The result of using M. Godron stability determination principle show that, there was less relativity between arbor species stability and the degree of fragmentation in Nonggang Nature Reserve. But in karst plate of Guilin, the relativity between arbor species stability and rate of area and girth of habitat relevance high, a positive correlation between the number of 0.865, that is greater than the perimeter and area, the higher the stability.
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