| Landscape fragmentation was one of major factors due to the loss of biodiversity. It was a composite process, which turned the primitive continuous habitats into several isolated remaining patches. It caused reduction in habitat area and internal habitat area, increase in the isolation of habitat fragments, truncation in corridors and changes in patch shape. Habitat fragmentation brought loses or degradation of habitat and change spatial patterns and accordingly induced the loss of biodiversity. The degree of habitat fragmentation was more great with the progress of society and the development of technology, and habitat fragmentation has become one of key issues in landscape ecology research.In this study, we investigated how island area size affected the distribution of plant species in the Thousand Island Lake region, compared several conservation scenarios for maximizing plant species diversity. Also, we compared the differences among different kinds of islands and analyzed on the relationships between island areas and species richness. The major results can be summarized as follows:1. We found 56 tree species and 79 shrub species in 74 islands that were surveyed. These islands and the tree and shrub species they contained were tabulated by island size and analyzed consequently. Our results showed that 11 tree species were affected by island area while 15 were not, and 30 in between being affected and unaffected. For shrubs, 24 species were unaffected, 16 were affected, and 39 species were in between being affected and unaffected to variability in island size. Comparing the cumulative numbers of tree, shrub, and all species in different scenarios of aggregating individual islands by small, medium, large, and mixed categories, respectively, we were able to examine how species richness changed with the increasing total area of habitat and which combination gave rise to the highest species richness. Our analysis revealed that, for a given total area of island habitat, mixing islands of different sizes gave rise to the highest cumulative plant species richness in terms of tree, shrub, or total species richness. The agglomeration of smaller islands resulted in the second highest species richness whereas large islands supported the lowest species richness for the same total area of habitat. Thus, our results suggest that islands of all sizes need to be considered for biodiversity conservation in the Thousand Island Lake region. 2. In our study, we investigated the species and number of trees and shrub in 74 sampling areas which were on 51 islands, compared the differences among different kinds of islands with One-way variance analysis (ANOVA) and analyzed on the relationships between island areas and species richness with regression analysis method. Our results showed that the species richness of tree was very significantly different (F=13.301, P=0.000) among all kinds of island islands, which was more significantly different between small and medium islands, small and large islands, and was significantly different between medium and large islands. The species richness of shrub was significantly different (F=3.927, P=0.026) among all kinds of islands, which was more significantly different between medium and large islands, small and large islands, but was not significantly different between small and medium islands. The species richness of plant was more significantly different (F=8.402, P=0.001) among all kinds of islands, which was more significantly different between medium and large islands, small and large islands, but was not significantly different between small and medium islands. The other indexes (Shannon-Wiener index, Simpson index and Pielou index) of tree, shrub and plant were not significantly different among all kinds of islands. Regression analysis showed that the island area had a logarithmic relation with species richness of tree, and appeared S curve with species richness of shrub and plant. The species richness of tree, shrub and plant increased greatly with the increase of island area at first, but the increase rate declined sharply when the island area was larger than 2 hm~2, 1 hm~2, and 0.8 hm~2, respectively. The correlativity between the island area and the Shannon-Wiener index of tree and plant submits to the curve of S, and the increase rate declined sharply when the island area was larger than 0.4 hm~2, 0.3 hm~2, respectively, but the island area and the Shannon-Wiener index of shrub had not significantly regression relationship. The correlativity between the small island area and the Shannon-Wiener index of tree and plant submits to the curve of S and the increase rate declined sharply when the island area was larger than 0.1 hm~2, 0.08 hm~2, respectively, but the small island area and the Shannon-Wiener index of shrub had not significantly regression relationship. The correlativity between area of medium and large island and the Shannon-Wiener index of shrub submits to the curve of S, and the increase rate declined sharply when the island area was larger than 2 hm~2, but the relationships between area of medium and large island and the Shannon-Wiener index of tree and plant were not significantly regression. The regression relationship between Simpson index and Pielou index of tree, shrub, plant and island area was not significantly.
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