Analysis On Spatial Distribution Patterns And Driving Forces Of Degraded Alpine Grassland In The River Basin Of The Yellow River Source Zone

Geographic information technology was used to classify and identify the degradation of alpine grassland(DAG)which was taken as research object in view of the river basin attributes and differences of ecological protection for the analysis of the main problems and key driving factors in alpine grassland based on River Basin(RB)of the Yellow River Source Zone(YRSZ).We explored and analyzed the distribution patterns and natural factors of the DAG in the RB of the YRSZ,so as to provide theoretical supports for the comprehensive management of DAG in the Qinghai area of the YRSZ.The results showed that:1.The total grassland area in Qinghai area of the YRSZ was 96 489.84km~2.The grassland types in the Qinghai area of the YRSZ were temperate deserts,swamps,alpine meadows,lowland meadows,mountain meadows,temperate grasslands,temperate steppe deserts,and alpine steppe.The concepts of"black soil beach"grasslands of black soil type,gravel-type and rock-type was proposed,and the vegetation coverage which is less than 70%was used as the identification of the DAG.The DAG area of"black soil beach"of black soil type in the Qinghai area of the YRSZ was 14 239.47 km~2,accounting for 14.76%of the total grassland area.The areas of"black soil beach"grasslands of gravel-type and rock-type were 2445.37 and 376.07 km~2,accounting for 2.53%and 0.39%of the total grassland area in the study area,respectively.The area of sandy grassland was 5739.75 km~2,accounting for5.95%of the total grassland area.2.There are a total of 878 different river basin catchments in the Qinghai area of the YRSZ,including two main stream units,172 tributary units at the first-level,333 tributary units at the second-level,149 tributary units at the third-level,14 tributary units at the fourth-level,and 23 dry-flow river units.With the reduction of the RB level,the average area of the RB decreases,the altitude increases,and the river network density increases.The dry-flow river units are mainly distributed in agricultural production areas,and their altitude and river network density are the lowest.3.Different types of DAG had different distribution patterns.In the RB,the proportion of black soil type of"black soil beach"and the area of sandy grassland were mainly distributed over the sunny slope and semi-sunny slope.The proportions of gravel-type and rock-type of"black soil beach”were mostly found in shady slope and semi-shady slope.Throughout all river basin catchments,the proportion of black soil type of"black soil beach"on the slope from[0,7)~oarea accounts for 57.86%;the proportion of gravel-type of"black soil beach”on the slope from[10,25)~oarea accounts for 44.32%;the proportion of rock-type of"black soil beach”in the[17,32)°area accounts for59.81%;the proportion of sandy grassland on the slope from[5,20)°area accounts for 59.81%.4.The most sensitive area of black soil type of"black soil beach"was located on the slope[0,7)°areas of sunny slope and semi-sunny slope in the river basin catchments of alpine meadows area,and the slope[0,15)°was degradation area.In the aggregate of 46803.33 km~2alpine grasslands area were under an extremely high risk of degradation to black soil type of"black soil beach".Distributed on the slope of[25,32)°area was the gravel-type of"black soil beach"degradation area,and the slope[32,68)°area was the degradation area of rock-type of"black soil beach".The degradation risk areas of gravel-type and rock-type of"black soil beach"were accounted for3999.19 km~2and 551.62 km~2,respectively.On the slope of[0,32)°area was the sensitive area of sandy grassland,which the sunny slope and semi-sunny slope are the sensitive area of degradation in total of 898.93 km~2.5.In the RB,the slope aspect had a greater impact on the ground temperature,and the slope had a greater impact on the average annual rainfall and spatial water and nutrients.Through the analysis of the vertical distance from the river,the distribution of residential areas in the RB was consistent with the distribution of DAG.Black soil type,gravel-type and rock-type of"black soil beach",sandy grassland,and severely deserted grassland were all most distributed within an area of[0,1)km to residential areas.Among them,the suitable activity area of rodents has the highest overlap with the degradation area of black soil type of"black soil beach".After redundancy analysis,slope aspect is the main factor affecting the formation of black soil type of"black soil beach"patches.Among all factors,the contribution rank of the slope to the size of the gravel-type"black soil beach"and the rock-type"black soil beach"is the highest.6.Human activities,soil types,slopes,and moisture in the RB had important influences on the distribution patterns of DAG.Among them,livestock grazing,rodent outbreaks and natural factors jointly affected the distribution pattern of DAG.Therefore,the key measures for the management of DAG on sunny slopes and beaches in the YRSZ should focus on reducing grazing,controlling rodent damage and resowing in the degraded grassland.