Temporal-spatial patterns and influencing factors of vegetation coverage in Bayanbulak Alpine Grassland, China

Based on MODIS NDVI data, the fractional vegetation cover (FVC) of Bayanbulak Grassland was measured from 2000 to 2020 by using a linear mixed spectral model, and the spatial-temporal variation patterns were analyzed by using the linear regression method. Besides, the influence of meteorological, terrain and land cover changes on regional FVC were analyzed. The results were as follows: 1) From 2000 to 2020, the average FVC of Bayanbulak Grassland was 46.19%, which showed a spatial distribution pattern of high in the west and low in the east. Areas with FVC greater than 60% were distributed in the northwest and south, accounting for 24.70% of the total area; areas with FVC lower than 15% were distributed at the edge of the study area. 2) FVC showed a trend of decreasing first and then increasing from 2000 to 2020, with an average annual decline rate of 0.093%; on the pixel scale, FVC remained basically unchanged in most areas, and the areas with a decreasing trend accounted for 24.86%, faceted in the central-east and north, and the areas with an increasing trend accounted for 10.54%, distributed in the edge of the middle and west of the study area. 3) FVC gradually decreased with elevation, and it was generally lower on the sunny slope than that on the shady slope. The effects of annual precipitation and annually average temperature on FVC showed significant spatial heterogeneity. About 10.70% and 13.99% of the regions had a positive correlation between FVC with the current year's precipitation and the last year's precipitation, and 8.23% and 11.11% of the regions had a positive correlation between FVC with the current year's average temperature and the last year's average temperature, and 8.23% and 5.35% of the regions had a negative correlation between FVC with the current year's average temperature and the last year's average temperature. The transformation of land cover types, especially the reduction of glaciers and permanent snow cover, contributed to the change of FVC.