Study On Grassland Coverage Change And Its Environmental Factors In Fenhe River Basin Based On Random Forest

Grasslands are an important component of the Earth’s terrestrial ecosystem and provide humans with various ecosystem services,such as food,raw materials,and cultural significance.The Fenhe River Basin is located in the transition zone between forests and grasslands,and the grassland types in the basin are diverse and sensitive to changes in environmental factors.Clarifying the spatial and temporal characteristics of grassland cover changes in the Fenhe River Basin and quantifying the impact of environmental factors on grassland cover changes are of great significance in the current context of global climate change.Based on a systematic analysis of the spatiotemporal distribution differences and trends of grassland cover and environmental factors in the Fenhe River Basin from 2001 to 2019,this study established a random forest model to evaluate the importance of environmental factors and analyze the impact of various environmental factors on grassland cover changes,as well as explore the spatial relationship between the main environmental factors and grassland cover changes.The research results can provide scientific reference for ecological restoration and agricultural production in the Fenhe River Basin.The main conclusions of this study are as follows:(1)From 2001 to 2019,the overall area of grassland in the Fenhe River Basin gradually decreased from north to south,with a greater decrease in the downstream region than in the middle and upstream regions.The NDVI of low-coverage grassland showed obvious interannual variations,with an overall upward trend;the NDVI of medium-coverage grassland fluctuated less but showed the most significant upward trend;the NDVI of high-coverage grassland showed a weak upward trend.(2)From 2001 to 2019,the net conversion of grassland to cropland in the Fenhe River Basin was 4,127.54 km~2,mainly occurring in the middle and downstream regions.The net conversion of grassland to shrubland was 595.62 km~2,mainly from medium-coverage and high-coverage grassland.The spatial distribution pattern of grassland in the Fenhe River Basin changed rapidly,with the distribution center shifting northward and the spatial distribution becoming more dispersed.(3)In different sections of the basin,the importance of slope was lower in the middle and downstream regions,with a smaller impact on grassland cover changes.Mean annual temperature and annual precipitation had significant impacts on grassland cover changes,but their importance varied greatly in different regions.Annual evapotranspiration had the greatest impact on grassland cover changes,with a fluctuating upward trend and regional differences.Overall,annual evapotranspiration,annual average temperature and annual precipitation are the main environmental factors.(4)In terms of the main environmental factors,grasslands in the Fenhe River Basin were mainly distributed in the range of annual evapotranspiration of 300mm-500 mm,mean annual temperature of 8℃-11℃,and annual precipitation of 400mm-600 mm.The correlation coefficient between grassland NDVI and annual evapotranspiration was 0.726,reflecting the wide and important influence of annual evapotranspiration changes on regional grass growth.The correlation coefficients between grassland NDVI and mean annual temperature and annual precipitation were0.118 and 0.304,respectively,and the magnitude of their correlations varied regionally.