Study On The Spatial Pattern And Its Controlling Factors Of Vegetation Coveragc In Thc Hilly Region Of The Loess Plateau

Vegetation fraction is one of the most important indicators of vegetation growth, and a major factor controlling soil erosion. The purpose of this paper is to analyze the spatial pattern of vegetation cover and the potential factors influencing vegetation coverage. Using SPOT NDVI and terrain data, with measured data for validation, TRMM precipitation data were downscaled. Determination coefficient between downscaling results and station data is0.863, which is slightly higher than determination coefficient of the original TRMM data with the actual site. Based on the DEM with resolution of15m, the land forms were divided using the combination of TPIs. Results show that the landscape type divide·by the smaller neighborhood of5grids and the larger neighborhood of7grids is best one for depicting the landforms of the study area. Using the ditch line data, we got the four land forms, which are ditches, ditch slope, tableland, and plain. The topographic wetness index was also calculated with the precipitation data as the weighting raster.NDVI and MSAVI were extracted on the basis of an aerial image with resolution of0.38m and measured vegetation cover data. Vegetation coverage was calculated using the ridge regression model. Moran’s I and Local Moran’s I index of vegetation cover suggest that vegetation within the watershed shows cluster distribution. Vegetation coverage is high in the north, while it is lower and broken in the south.In the middle of the channel with the main direction from east to the west, there is significant difference in vegetation coverage between shady slope and sunny slope. The reason for this is that the cosine of aspect has a very strong positive correlation with the vegetation cover, which is much greater than other factors. There is a strong negative correlation between solar radiation and vegetation coverage at a large scale. Vegetation coverage on ditch slopes is higher than other three landscape types. There is significantly positive correlation between slope and vegetation coverage at all watershed scales. As slope is larger, vegetation coverage is higher. it is corresponding with the regional distribution of location with a large slope. In the ditch along the slope near the maximum slope in the upper part of the ditch, it is easy to form runoff, and water conditions are good for vegetation growth in those regions.The vegetation coverage is generally low in the main channel. The TWI is high in such location. However, nearly80%of rainfall is in the form of storm, which increases soil erosion. The small amount of rainfall cannot enter the main channel. Also, the land use types in the main channel are residents, roads, and mining land with intensive human activities. Land use degree is very high, resulting in generally low vegetation cover in the region. There is similar distribution with the same causes in the flat terrain of the.tableland area.