Diversity Patterns Of Plant Constituents And The Maintaining Mechanism In Fragmented Habitats In The Songnen Meadow

Biodiversity refers to the total life on the Earth and is the result of evolution of millions of years, which is the material basis of human survival. However, the natural vegetation became fragmented under the unreasonable impact of human activities, which resulted in the significant decrease in species diversity. Not surprisingly, the maintenance mechanism and patterns of plant species diversity had become the research focus. Firstly, the existing vegetation characters were analyzed in this paper comparing with the data investigated in 1981. Secondly, six different plant communities were surveyed to analyze the impact of habitat fragmentation on species diversity. Finally, a represent community in the recovery stage, Leymus chinensis + Kalimeris integrifolia community, was analyzed to discover the change of community structure across three different patch scales, and clarified the maintenance mechanism of plant diversity on basis of plant taxon and ecological type. Furthermore, an effectively new analytical method was proposed. The results were as follows:1 There are 72 species belonging to 24 families and 62 genus in the existing community comparing with 97 species belonging to 29 families and 67 genus in 1981, and the decrease was 5 families, 5 genera, 25 species, respectively. The total proportion of B, C and D levels decreased in frequency distribution and the community evenness increased. In terms of areal type structure, the Northeast-Dahurica areal type was the new components and Mongolian-Dahurica-North China areal type were the disappeared components. In terms of ecological type structure, the hemicryptophyte, limb type and taproot type account for the most of life form, plant growth form and root growth form respectively. The region community still had the typical characteristics of temperate grasslands and was controlled by the large bio-climatic.At the local community level, under the impact of local ecological factors, the changes of ecological type structure varied in different communities. In L. chinensis community, the species richness, evenness and diversity decreased dramatically. And in herbosa and alkaline community, both the species richness and diversity increased. At the same time, the biomass of species-rich community was more sensitive to the change of environmental conditions, while communities with fewer species had a little change in biomass.2 There were a total of 87 vascular plant belonging to 27 families and 68 genus in the six communities. Most species had a narrow distribution and a lower local abundance, while few species had a wider range and higher local abundance, and this distribution trends varied in different communities. The endemics were positive correlation to y diversity. There were positive correlation betweenα,βdiversity and y diversity. In terms of species diversity of the six metacommunities, in each community type, the species richness and Shannon-Weinner index increased as the patch area increased both in power function. Thus, the species-rich communities were most sensitive to habitat fragmentation. For the purpose of species conservation, the species-rich communities should be protected firstly. The communities with lower species richness could be protected at second due to the slight impact of habitat fragmentation.3 In terms of the effects of habitat fragmentation on plant community structure, the species composition of plant communities changed dramatically. On small patches most species had narrow distribution and lower local abundance. On the other hand, most species distributed widely and had a higher local abundance on large patches. In terms of ecological type structures, the geophyte of life form increased significantly on large patches (p<0.05). The bottom of lotus seed type and endlong type had significant difference among small, medium and large patches. And the root growth form hadn't significant difference among s three patch scales (p>0.05). However, the three ecological types were dominated by taproot type, limb type and hemicryptophyte. The biomass among three patches scales had not significant difference. The ecological type structure and biomass structure of community had lower variation and didn't change dramatically with the loss of species. The response of plant community to habitat fragmentation depended on the biological properties of species. The response to habitat fragmentation varied among different species in different degree of habitat fragmentation when different species was lost.4 At the local community level, Shannon-Weinner indexes, Simpson indexes, Whittaker indexes and Bray-Curtis similarity indexes all fluctuated greatly. However, at the metacommunity level, there was a positively power correlation between each diversity index and patch area. At the local community and metacommunity level, the higher taxonomic units such as family and genera were more sensitive to space variation of plant diversity pattern than ecological type. There were high turnovers and low habitat heterogeneity in small and medium patches, while there were low turnovers and high habitat heterogeneity in large patches. The maintenance mechanism in local community distributed in fragmented habitats in Songnen Plains were proposed. The plant diversity was maintained by the colonization-extinction process on medium and small patches and by habitat heterogeneity on large patches. At the same time, a new method was put forward to analyze the spatial patterns of plant diversity, that is, family and genera can be applied in spatial analysis of species diversity. The ecological type diversity was prone to be affected by random environment, and could be used as a complementary analytical tool.