| As an extreme land degradation phenomenon,karst rocky desertification(KRD)is one of the most prominent problems in the interweaving of social economy and ecological environment in the karst area of southwest China,meanwhile,it is also a hot and difficult problem in the academic circle for a long time.How to scientifically understand the temporal-spatial evolution process of KRD and its driving mechanism is the initial prerequisite and key to carry out the control of KRD.Qujing City is situated on the upper reaches of the Pearl River with special geographical.The extensive development of KRD not only weakens the water conservation ability of the upper reaches of the Pearl River,but also seriously hinders the ecological civilization construction and socio-economic development of Qujing City,and poses a potential threat to the ecological security of the lower reaches of the Pearl River Basin.Accurately identified and reveal the temporal and spatial dynamic evolution rules of KRD over a prolonged period of time,as well as quantitatively reveal the driving mechanism of karst natural environment and anthropogenic factors and its interaction on the formation and evolution of KRD are essential for the integrated treatment of KRD and the improvement of karst ecological environment.Therefore,this study selected the Landsat TM/OLI data sets as the main data sources from 1987-2020,The key indexes of rocky desertification degree evaluation were selected and the method of rocky desertification information extraction was discussed,and then extracted the spatial-temporal distribution information of KRD in Qujing City from 1987 to 2020,this paper further described the spatial-temporal evolution law of KRD in Qujing City in the past 30 years from aspects of the direction,scale and rate of KRD evolution.Finally,combined with multi-source data,such as meteorological data,socio-economic statistics data and so on that the related factors which may affect the occurrence and development of KRD were selected from two aspects of anthropogenic factors and natural factors,and then adopted the method of geographical detector for detected year by year and also quantitative analysed the driving factors affecting the evolution process and its correlation of KRD in Qujing City.The main contents and conclusions are as follows:(1)Study on information extraction technology of KRD based on Landsat TM/OLI data.Used bedrock exposure rate,fractional vegetation coverage and slope as the evaluation indexes of rocky desertification degree,and combined with Google Earth high-resolution images to determine the interpretation signs and image characteristics of different degrees of KRD,the classification method of KRD in Qujing City was discussed and analysed,and the KRD was divided into six grades: none obvious KRD(NKRD),potential KRD(PKRD),lightly KRD(LKRD),moderate KRD(MKRD),severe KRD(SKRD)and extreme KRD(EKRD).The decision tree method is adopted to extract the grade information of rocky desertification and evaluate the accuracy by combining the threshold value of each evaluation index.The overall accuracy is 82.50%and the Kappa coefficient is 0.771.(2)Study on spatial-temporal evolution of KRD in Qujing City.From 1987 to 2005,the deterioration of KRD in Qujing was intensified,which was mainly affected by high-intensity,overloaded and unreasonable human activities.From 2005 to 2020,KRD is mainly affected by natural disasters.Although after years of continuous control,KRD in some areas has deteriorated,on the whole KRD in the study area has developed towards a benign direction,and the ecological environment has gradually recovered.The KRD are mainly distributed in Huize County,Fuyuan County,Luoping County,Shizong County and Luliang County and their boundary areas,and their area changes are relatively slow,and the PKRD and LKRD are highly unstable and easily transferred to higher grades of rocky desertification.Therefore,attention should be paid to the comprehensive control of rocky desertification.(3)Annual detection and analysis of driving factors influencing the temporal and spatial evolution of KRD in Qujing City.In recent 30 years,the main driving factors affecting the development and evolution process of KRD in Qujing City were the gross agricultural output value(0.221-0.281),the total population(0.201-0.232)and the cultivated land area(0.213-0.216),and the q values fluctuated between 0.20-0.28.The explanatory power of factors such as per capita GDP,total population,population density and distance from residential areas on KRD gradually decreased,indicating that the influence of these factors on KRD in Qujing City was gradually weakened.The Q values of factors such as distance from road,average annual temperature and elevation gradually increased,it is show that the development and evolution of KRD were gradually influenced by these driving factors.(4)Detecting and analyzing the interaction of driving factors of the temporal and spatial evolution of KRD.The detection results show that: slope∩cultivated area(q=0.465)> cultivated area ∩ total population(q=0.374)>cultivated area∩ population density(q=0.302)> annual average precipitation ∩ slope(q=0.283)> cultivated area∩distance from settlements(q=0.278).Slope,annual average precipitation and away from residential areas from the interaction between performance for nonlinear enhancement,population density,between arable land and agricultural output is double factor enhancement,shows that slope,annual average precipitation and distance from population centres factor with the interaction of the factors such as arable land,agricultural output can enhance more influence on KRD development and evolution process,the occurrence and development process of KRD is the result of variety driving factors interaction. |
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