Study On Vegetation Cover Change Characteristics Of Slope And Gully Landform In Yanhe River Basin

The Yanhe River Basin is a key area of the Loess Plateau for returning farmland to forest,slope and gully are two different and unique geomorphological landscapes in this area.In ecol-ogy,it is important to investigate the recovery of vegetation cover on the slope and gully land-scapes of the Yanhe River Basin after the implementation of the ecological projects such as returning farmland to forest,and to assess the response mechanisms and principles of vegetation cover to natural elements,land use and human activities.Previous studies have mainly focused on the overall vegetation cover changes in the Yanhe River basin,and the vegetation cover characteristics of different landscapes at small scales have been slightly under-explored.There-fore,this study investigated the vegetation cover change characteristics of the Yanhe River basin as a whole and the slope and gully landform areas within the basin from 2000 to 2020 based on Normalized Difference Vegetation Index(NDVI),Fractional Vegetation Coverage(FVC),as well as rainfall and land use data,combined with trend analysis and abrupt change point anal-ysis.And on this basis,linear regression and residual analysis were used to analyze the mecha-nism of spatial variation of NDVI in the Yanhe River basin and the relative contribution of climate change and human activities to interannual NDVI changes.The main conclusions are as follows:(1)The recovery of vegetation cover in the Yanhe River basin from 2000 to 2019 was obvious(the average annual trend rate was 1.30%),but showed segmentation characteristics,among which the recovery of vegetation cover was rapid from 2000 to 2008(the average annual trend rate was 2.00%);the recovery of vegetation cover slowed down from 2009 to 2019(the average annual trend rate was 0.70%),and some areas were degraded.(2)From 2000 to 2020,the NDVI of gully areas in the Yanhe River basin showed an increasing trend with the increase of slope NDVI,and the correlation was strong(R~2=0.967),and the values of slope and gully NDVI were similar.The NDVI of gully and slope differed in different sub-basins,and both gully and slope NDVI showed positive correlation with the pro-portion of forest land area in the sub-basin,and the increasing trend of gully NDVI was more significant than slope NDVI;both gully and slope NDVI showed negative correlation with the proportion of cultivated land area in the sub-basin,and the decreasing trend of gully NDVI was more significant than slope NDVI.(3)From 2000 to 2020,the arable land area in the Yanhe River Basin showed a signifi-cant trend of decrease,with the proportion of arable land area decreasing by about 11%,and the area of forest land and grassland showed an increasing trend,with the area of forest land increasing by about 4%and the area of grassland increasing by about 11%.Spatially,the areas of cropland converted to woodland and grassland are mainly distributed in the northern and southeastern parts of the Yanhe River Basin.(4)The correlation between NDVI changes and rainfall in the Yanhe River basin from2000 to 2019 was weak.Rainfall was not the dominant factor of NDVI changes in the area,and human activities showed a strong positive correlation with NDVI changes in the Yanhe River basin.The average annual contribution of human activities to NDVI was 1.29%.The area share of different land types had different effects on slope and gully areas,among which the area share of cultivated land showed a negative correlation with NDVI of slope and gully,and the vegetation cover of slope and gully was the lowest when the area share of cultivated land was about 40%.The area of forest and grassland was positively correlated with the NDVI of slope and gully,and the increase of forest area was the main reason for the increase of NDVI of slope and gully.