The Study Of Vegetation Community Characteristics And Evaluation Of LUCC In The Semi-arid Wetland

As the unique climate characteristics and ecological characteristicsof arid and semi-arid wetlands in Yanchi County, we want to have an overall understanding of dynamic change of wetland's cause based on community-scale and landscape-scale. We have an overall understanding of dynamic changes of wetlands and lay a solid foundation for wetlands climate research, wetland conservation, process studies of wetlands and restoration study of degradation wetland.In community scale, there were three reaearchs such as vegetation biodiversity, vegetation community and niche breadth and niche overlap. We analysis and discuss the dynamic fluctuations of vegetation through these three aspects of community scale. In landscape scale, there were two works to do:1) to shoot and collect digital quadrat photos and the satellite images of the study area, we analysised correlation of two survey methodologies of wetland vegetation coverage.2) Based on three satellite images of1999,2004and2010. To predict LUCC of2015and2020through the use of the Markov chain, we mainly analysis and discuss ecosystems services value of LUCC, mainly about wetland. The conclusions are as following:(1) In Siertan vegetation indices of east and north line transect are higher than that of south and west line transect. The main reason of change of each vegetation indices are soil moisture and rainfall in growth season, in addition, terrains rise and human activities.(2) The main vegetations of "three strips" are summed up, according to results of cluster analysis and principal component analysis and experience of survey. There are three main vegetations in wet strip, respectively Kalidium foliatum, Suaeda salsa and Nitraria tangutorum. There are eight main vegetations in ecotone strip, respectively Polygonum sibiricum, Peganum harmala, Bassia dasyphylla and so on. There are eight main vegetations in arid strip, respectively Heteropappus altaicus, Sophora alopecuroides, Lespedeza davurica and so on.(3) Based on niche breadth and niche overlap, results are that:S. salsa, N. tangutorum and K. foliatum's niche breadth are biggest in wet strip. There are many plant species in ecotone strip, lot of them could be resistant to moist and drought. B. dasyphylla, Salsola ruthenica and Psammochloa villosa's niche breadth are bigger in ecotone strip. In arid strip niche breadth of H. altaicus, S. alopecuroides and Thermopsis shischkinii were increased. The reault of this research shows that niche breadth and niche overlap have not obvious linear relationship.(4) To make a regression analysis between vegetation coverage measured by digital photographs of the wetland and NDVI of satellite photos, the results showed that they have a high fitting degree. Furthermore, we know that vegetation coverage can be well reflected by digital photographs.(5) The wetland was mainly tranfered into grassland and farmland of1999-2004, other types of landuse made very small contribution. The wetland of1999-2004was generated from grassland and farmland. The tranfered amount is greater than the generated amount in1999-2004. The wetland was mainly tranfered into grassland of2004-2010; the wetland of2004-2010was generated from grassland and farmland. The generated amount is greater than the tranfered amount in2004-2010. On the recent decades wetland of the northwest increased due to protection policies making by government.(6) The trend of the ecosystem services value was first increased and then decreased from1999to2020. In the first-type services the regulating service (about50%) was the highest, followed by support services, supply services and culture service, from more to less there were9single ecological service value as follows:soil conservation, biodiversity conversation, climate regulation, water conservation, waste disposal, air regulation, landscape regulation, food production and raw material production. Among the secondary services, ecosystem services value are mainly soil conservation, biodiversity conversation, climate regulation, ecosystem services value of food production and raw material production is minimum. Generally, the contribution rate of woodland and grass is the largest in arid region of northwest of China, and followed by wetland.