| Rock desertification is a unique ecological phenomenon of desertification in southwestern and southern China,mainly characterized by land degradation and bedrock exposure.Rock desertification not only affects the local ecological environment and socio-economic development,but also threatens the national food security and ecological security.Therefore,dynamic monitoring and evaluation of rock desertification is an important basis for rock desertification control and ecological construction.Taking Xupu County of Hunan Province as an example,this study used multi-temporal and multi-resolution Landsat and Sentinel-2 remote sensing image data,and adopted methods such as support vector machine classification,index evaluation and regression analysis to extract and analyze the indicators such as land cover change,vegetation coverage and bedrock exposure rate in the study area,and then graded the rock desertification intensity in the study area,and explored its spatial-temporal evolution and internal transfer laws.The main research conclusions are as follows:(1)Support vector machine classification method can effectively classify the land cover in the study area,with an overall classification accuracy of 84.35%and a Kappa coefficient of 0.79.During the period from 2000 to 2021,the area of grassland,cropland,water body and other land types in the study area showed an increasing trend,while the forest area experienced a decrease followed by an increase due to urban development.(2)Vegetation coverage is an important indicator reflecting the vegetation growth condition,and a key factor for evaluating the degree of rock desertification.This study used the improved normalized difference vegetation index(NDVI)to invert vegetation coverage and analyzed its correlation with bedrock exposure rate.The results showed that during the period from 2000 to 2021,the vegetation coverage in the study area showed an overall increasing trend,and the growth area was mainly concentrated in areas with vegetation coverage greater than 80%;the proportion of areas with bedrock exposure rate lower than 16%showed a significant increasing trend,while the proportion of areas with bedrock exposure rate between 30%and 45%decreased significantly;vegetation coverage was significantly negatively correlated with bedrock exposure rate(R=-0.76),indicating that the higher the vegetation coverage,the lower the bedrock exposure rate.(3)Divided the rock desertification intensity level according to two indicators:vegetation coverage and bedrock exposure rate and analyzed the spatial distribution characteristics of rocky desertification in Xupu County,The results showed that the rock desertification in the study area mainly showed a patchy and thin strip distribution,dominated by potential,mild and moderate rock desertification,among which the severe rock desertification in the central and northern regions was more serious and deeper.During the period from 2000 to 2021,4.90%of the study area showed a significant deterioration trend of rock desertification intensity,mainly concentrated in some areas of the central and southern parts of the study area.In addition,16.99%of the study area showed a significant improvement trend of rock desertification,which was relatively evenly distributed.(4)Useing transfer matrix method to analyze the internal transfer law of rock desertification in Xupu County.The results showed that during the period from 2000 to 2021,rock desertification transfer mainly occurred in mild and moderate rock desertification areas,and overall rock desertification intensity improved.The improvement rate of severe rock desertification areas was the highest,while mild and below rock desertification areas had different degrees of deterioration.Generally speaking,rock desertification control in the study area has achieved certain results,but in the future,it is still necessary to scientifically formulate plans,increase comprehensive control efforts and strengthen enforcement measures to improve rock desertification problems. |
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