Spatiotemporal Changes Of Soil And Vegetation In Response To Anthropogenic Activities

Since the Open Policy in1978, socioeconomics developed rapidly in China, resulting in extensive urban expansion and continuous declines of ecological environment quality. As important components of ecological environment, soil and vegetation significantly impact on the structure and function of ecosystems. It is senticific to protect, utilize, and manage natural resources at watershed scale, thus, quantifying the response of soil and vegetation to anthropogenic activities can provide critical inferences for monitoring, assessing, and protecting soil and vegetation resouces. With a case of Tiaoxi watershed, China, this study characterized the dynamics of anthropogenic activities and their impacts on soil and vegetation at watershed scale, using remote sensing, geographical information systems and landscape ecology. Specifically, anthropogenic impacts on vegetation were described from two aspects:landscape strcutre and quality. The main results and conclusions were summarized as follows.Total population showed linear increasing trend in Tiaoxi watershed between1978and2008, while non-agricultural population proportion and gross domestic product (GDP) experienced exponential growth. At watershed scale, the area of built-up land increased by700%. Besides, built-up land became more fragmentation (increase in patch density), more irregular (increase in area-weighted mean shape index), more connected and more aggregated (increase in connect index and aggregation index). At sub-watershed scale, landscape patterns of built-up land showed great spatiotemporal heterogeneity. For period between1994and1999, built-up land expansion was more extensive, vigorous and irregular than the other periods.Between1978and2008, soil sealing was extensive across Tiaoxi watershed. Paddy soils, expecially those of the highest quality (the first and second level), were the first victims. Soil landscape patterns became more fragmented (patch density increases115%), less diverse (Shannon diversity index decreases0.57%), less connected (connective index decreases29.52%), and less aggregated (aggregation index decreases0.89%). Anthropogenic activities, at sub-watershed scale, had significant impacts on soil landscape pattern changes. Generally, there were significant correlations between anthropogenic activity intensity (AAI) and total area, patch density, area-weighted mean shape index and aggregation index of soil landscapes in all period intervals, while the relationships between soil landscape metrics and distance to town centers and roads were significant only in certain intervals, indicating that the impacts from AAI were stronger than those from distance to town centers and roads.RUSLE model revealed that soil erosion risk was intensified and areas with high risk erosion continued to increase between1985and2008. At sub-watershed scale the impacts on soil erosion risk from AAI were stronger than those from distance to town centers and roads; AAI was significantly correlated with soil erosion during all the temporal intervals, while the proximity factors were only significantly during the period between2003and2008.Given the vegetation structures in Tiaoxi watershed, area of farmland decreased, area of orchard increased and area of forest decreased between1985and2008. Farmland landscapes, at watershed scale, became more fragmented and less aggregated; forest landscapes became more fragmented and irregular, and less connected and aggregated. At sub-watershed scale, the impacts from anthropogenic activities were stronger on farmland landscapes than those on orchard and forest landscapes. AAI led to increase in patch density, decrease in area, edge density, irregular, connectivity and aggregation of farmland landscapes; distance to town centers and roads had significant correlations with farmland total areas and patch density. For orchard landscapes, anthropogenic activity intensity revealed significant correlations with total area, patch density, edge density and connectivity, and distance to town centers and roads had significant correlations with patch density. For forest landscapes, AAI showed significant correlations with patch density, edge density, area-weighted mean shape index and connectivity.Vegetation quality changes in Tiaoxi watershed between2000and2008was analyzed through normalized differential vegetation index (NDVI). Results indicated that annual mean value of NDVI increased a little, and monthly mean value of NDVI increased at the beginning and then decreased, with a peak value in summer. Vegetation quality was lower in north-central and east areas, and higher in sounth-central areas. Besides, high quality of vegetation mainly existed in zones with elevation of200-1000meter, with slope of45degree and with north aspect. At sub-watershed scale, AAI had significantly negative correlations with NDVI for farmland, orchard and forest, meaning that increase of anthropogenic activity intensity can cause the decline of vegetation quality. Besides, distance to town centers and roads had significant correlation with NDVI for farmland and forest, while had no significant correlation with NDVI for orchard.The major contributions of this study were:(1) quantifying the impacts from anthropogenic activities on soil sealing and soil landscape patterns;(2) quantifying the impacts from anthropogenic activities on soil erosion at sub-watershed scale; and (3) quantitatively investigating the impacts from anthropogenic activities on vegetation structure and quality. However, there still existed several limitations and further study should focus on more spatial scales of anthropogenic activity impacts, different spatial regression models, division of watershed ecosystem, more vegetation quality index, temporal span of NDVI.