Study On The Change And Stability Of Landscape Pattern In Qilian Mountain Nature Reserve

The distribution data of 8 landscape types in Qilian Mountain Nature Reserve from 1989 to 2019 were obtained based on Google Earth Engine.Landscape pattern indices were selected from class level and landscape level to indicate the change of landscape pattern characteristics in the study area based on Arc GIS and Fragstats4.2software.On this basis,the principal component analysis method was used to determine the weight,and according to the selected landscape pattern indexes,the comprehensive evaluation models of landscape stability at two levels were established respectively to evaluate the landscape stability of the study area.Finally,the spatial distribution of landscape stability was obtained by the Kriging interpolation method,and its distribution characteristics were analyzed.The main conclusions are as follows:(1)The alpine desert and grassland were the main landscape types in the study area.The area of alpine desert decreased by 3130.45 km~2;Grassland area increased by4223.62 km~2;Forest area decreased by 261.09 km~2;The net shrub area decreased by242.47 km~2;The glacier/permanent snow cover area decreased by 662.18 km~2;The proportion of wetland,residential area and farmland area was small,and the change of area was not obvious.(2)Characteristics of landscape pattern on class-level:The dominant landscape changed from alpine desert to grassland;The degree of grassland fragmentation was the largest and showed an increasing trend;The shape complexity of grassland and shrub is more complex than that of other landscapes.The shape complexity of grassland is stable,but the shape of shrub tends to be simple;The dominance of alpine desert and grassland in the landscape makes the degree of convergence and connectivity of alpine desert and grassland higher than that of other landscapes.The degree of convergence of the two landscapes does not change much,but the degree of connectivity increases first and then decreases.Glaciers/permanent snow,due to their high altitude and patchwork distribution,have a degree of aggregation similar to grassland but low connectivity.(3)Characteristics of landscape pattern on landscape-level:The overall connectivity of the landscape was gradually decreasing,and the same landscape tended to be centralized;The degree of landscape fragmentation showed a decreasing trend;The change of the maximum patch area index verified the development process of the desert landscape dominance decreased and the grassland landscape dominance increased;The overall shape of the landscape tended to be simplified;The diversity of landscape types was low,which indicated that the distribution trend of landscape types was uneven,and the landscape was dominated by the alpine desert and grassland landscape.(4)Characteristics of Landscape stability:The stability of alpine desert and grassland was higher than that of other landscape types,but the stability of alpine desert showed a downward trend,while the stability of grassland showed an upward trend;Glacier/permanent snow stability was decreasing;The stability of forest landscape was on the rise;The stability of shrub showed a fluctuating state;The stability of wetlands,farmland and residential area was poor during the study period.During the study period,the landscape stability showed a decreasing trend,and the area decreased mainly in the moderately stable area and the very unstable area,while the area of the very stable area and the general stable area increased,indicating that the environmental governance had achieved success,but the environmental protection in the moderately stable area still needs to be paid attention to.The spatial stability of the landscape in the reserve is"higher in the southeast,lower in the northwest,and fluctuating in the middle".The spatial distribution of landscape stability in the reserve showed the characteristics of"high in southeast,low in northwest,and fluctuating in the middle".