Sdudy On The Change And Driving Force Of Vegetation Cover In Yangtze River Basin

For a long period, the ecological environment in Yangtze River Basin became increasingly prominent which was influenced by many factors including nature factor and human factor, mainly including flood and waterlogging disasters, geological disaster water pollution, soil erosion, biological species decreasing, etc al.Soli erosion was particularly serious, and had become the primary environmental problems in Yangtze River Basin, which was coursed by the number of vegetation dropped sharply. The growth of vegetation was influenced by many factors, which mainly can be attributed to two types. One is nature factors, including terrain and climatic factors, the other was human factor. From the long term, natural factors as the main influencing factors determined to spatial distribution of vegetation pattern, and the human factors can also cause variation of the pattern of vegetation in the short term. Based on SPOT/NDVI data during1999～2010and climate data, terrain data, social-economic data, combined with linear regression trend method, spatial interpolation method, correlation analysis method, the paper researched the spatial and temporal variation of NDVI in Yangtze River Basin. The correlation between NDVI and terrain,climate,human fators was explored, to prupose to explain the spatial and temporal variation of NDVI,which could provide some essential theoretical basis for Yangtze River Basin Shelter construction and the regional ecological environment improvement. The main concludions for this research as below:(1) The variation trend of mean annual NDVI was increased during1999-2010in Yangtze River Basin, and the increase rate was0.050/10a that showed the vegetation coverage condition had been improved. Based on the distribution of spatial variation of mean annual NDVI showed that the value in the east and west was higher than the value in the middle of Yangtze River Basin. The proportion of girds which the NDVI was significantly increased was51.82%in P<0.05, and only0.73%was significantly decreasing. It was descriped that the vegetation covering in most regions were improved and only small proportion was degradating nearly12a.(2) The seasonal NDVI was existed spatial and temporal variation under the seasonal scale. The mean seasonal NDVI was increased during1999-2010, it was same to the trend of mean annual NDVI. The variation rate of seasonal NDVI was0.060/10a, 0.050/10a,0.060/10a,0.030/10a respectively, but the spring and autumn NDVI were increased significantly. Over45%of the grid in spring, summer, autumn was a significantly increased, and only27.71%of the gird in winter was increased. But it was no significant change in four seasons.(3) The different vegetation types NDVI were increased trend during1999-2010in Yangtze River Basin, and the variation rate were0.050/10a,0.020/10a,0.040/10a,0.070/10a respectly. The mean annual NDVI order of different vegetation types was woodland> cultivatedland> grassland> shurbland. Trend of mean seasonal NDVI of mainly vegetation was increased during1999-2010in Yangtze River Basin. The order of mean seasonal NDVI was cultivatedland> woodland>grassland>shurbland in spring, autumn, winter, and the order was cultivatedland> woodland=grassland> shurbland in winter.(4) The mean annual NDVI of different regions was increased trend in Yangtze River Basin, the maximum increased rate was midstream, the second was upstream, and the downstream was minimum. In the nine river of Yangtze River Basin, the mean annual NDVI of Poyang lake was maximum, and jinshajiang river was minimum.(5) Mean annual NDVI of different altitude scale took changing with altitude, in a certain range, the higher the altitude, the greater the NDVI. But the rule would be contrary over this range. The NDVI of each altitude grade showed an increasing trend during1999-2010, but the higher altitude scale, the lower increasing rate. In some low altitude region, the rate of mean annual NDVI was increased quickly. In the range of a certain slope, with the higher slope gradient,NDVI was gradually increasing, but the increase rate was reducing as higher slope gradient. It indicated that the changing of NDVI mainly occurred in some low gradient region. Different aspect NDVI was sunny slope> semi-sunny slope> semi-shady slope> shady slope, and the variation rate of sunny aspect was quicker than others, the shady aspect was the slowest.(6) The correlation coefficient between mean annual NDVI and temperature was greater than the correlation coefficient between NDVI and precipitation, indicating that the influence of mean annual temperature exceeded annual precipitation. Four seasonal NDVI was positively associated with the temperature, and negatively associated with precipitation, and spring NDVI was significantly associated with temperature. The rate of positive correlation coefficient was greater than the negative what was between mean annual NDVI and temperature, precipitation from the spatial variation distribution in Yangtze River Basin. The rate of positive correlation between four seasonal NDVI and seasonal temperature was greater than the negative correlation. The rate of negative correlation between seasonal NDVI and seasonal precipitation was greater than the positive correlation besides spring. It existed1-5months lag correlation between January, April, June, July NDVI and temperature, precipitation.(7) It was not significantly and positively associated with woodland, grassland, cultivatedland NDVI and mean annual temperature, four mean seasonal temperature, except shurbland. Woodland NDVI ans spring precipitation showed no significant positive correlation, and negatively related with mean annual precipitaton, in addition,showed significantly and negatively correlated with summer precipitation. It was no significantly positive correlation between shurbland NDVI and precipitation in spring, autumn. Grassland NDVI and precipitation in spring, winter showed weak positive correlation, and negative correlation with annual precipitation, precipitation in summer, autumn. Cultivatedland NDVI and annual precipitation, four seasonal precipitation showed no significantly negative correlation.(8) Mean annual NDVI was decreased with the increasing polulation density. The greater mean annual NDVI, the lower population density, it showed that the dondition of vegetation coverage was good in some low population density. Mean annual NDVI and GDP showed significantly negative correlation (P<0.05), it indicated that the vegetation had been greater human influence in some higher economically developed region, and the NDIV was lower. However, the vegetation had been weaker human influence in some economy backward area, and the vegetation activities was relatively strong in these areas.