| In order to fundamentally curb the deterioration of the ecological environment,improve the ecological environment,control the soil erosion,restore and develop forest resources,protect the biodiversity and promote the sustainable development of social economy,the Natural Forest Protection Project(NFPP)in 1998 has been implemented and lasted 20 years.It is of great significance to analyze and study the change of vegetation cover and the dynamic characteristics of soil erosion before and after the NFPP.Setting Xiangcheng,Tibetan Autonomous Prefecture of Garze,where the main natural forest distribute in Western Sichuan,as the research area,this paper used the remote sensing images of 1996,2006 and 2015 as the data resources to classify the vegetation cover types by decision tree method and analyze the spatial distribution and dynamic changes of vegetation cover of the research area in recent 20 years.Besides,this paper quantitatively estimated the amount of soil erosion in the research area in the last 20 years and graded zoning for soil erosion by selecting factors such as vegetation coverage,precipitation,topography and soil type and using the Universal Soil Erosion Equation(USLE).The spatial divergence of soil erosion intensity grades on different vegetation cover types,vegetation coverage,elevation,slope,and valley density was analyzed and the evolution of soil erosion in the research area in the past 20 years was also summarized in this paper.The main findings of this paper are as follows:1.In 1996,2006 and 2015,the vegetation cover of the research area was mainly occupied by forest land.From 1996 to 2015,the change of forest land area generally showed an increasing trend.In 1996,the forest land area was 285,620.62 hm~2,298,813.56hm~2 in 2006,and 308055.15 hm~2 in 2015.The ratio of forest land area in the three periods were 57.78%,60.45%and 62.33%to the whole land area;2.From 1996 to 2006,the changes in vegetation cover were mainly transformed between forest land,grassland,and other land uses.The conversion mode was mainly grassland to forest land and other land use changed to grassland.During the 10 years,the net increase of forest land and other land uses areas were 13192.95 hm~2 and 1800.36 hm~2.The grassland area and cultivated land area were reduced by a net amount of 16892.22 hm~2and 554.19 hm~2.From 2006 to 2015,the vegetation cover changes mainly happened between the forest land and the grassland.Among them,the forest land had an increase of19729.34 hm~2,a decrease of 10487.76 hm~2,which meant a net increase of 9241.58 hm~2.Most of the transferred area was grassland,which was 8262.21 hm~2,and the main part of the transfer was also grassland,which was 17478.14 hm~2.3.In the three periods of 1996,2006 and 2015,the intensity of soil erosion in the research area was mainly moderately eroded,and the erosion areas were 199259.73 hm~2,193637.79 hm~2 and 191182.59 hm~2.From 1996 to 2006,the evolution of soil erosion intensity was mainly transferred between moderate erosion and intensity erosion.Among them,the largest transferred area happened between the moderate erosion and the intensity,whose area was 29147.31 hm~2,and the followings were the intensity transferring to the moderate,the intensity to the pole intensity,and the mild to the moderate,which were20000.25 hm~2,19192.95 hm~2 and 12747.24 hm~2 respectively.4.From 1996 to 2015,the main intensity of soil erosion in the research area generally increased with the increase of elevation and slope,and weakened with the increase of vegetation coverage;vegetation cover type and soil erosion intensity were closely related,and the main intensity of soil erosion of different vegetation cover types was different during the same period,and the main intensity of soil erosion of same vegetation cover types was identical during the different period;the soil erosion had no obvious differentiation with the density of the valley.Based on the combination of climatic data,remote sensing data of different periods and topographic data,this paper discusses the dynamic changes of vegetation cover and the spatial distribution characteristics and shift of soil erosion in Xiangcheng County to learn about the status of vegetation cover and soil erosion in Xiangcheng County and also provides reference for the ecological restoration of vegetation,ecological restoration and soil and water conservation in Xiangcheng County. |
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