Satellite view of vegetation dynamics and drivers over southwestern China

Abstract

Vegetation is a key component of the terrestrial ecosystems, its dynamics serve as an indicator of vegetation health and ecosystem stability. However, the vegetation dynamics and its responses to climatic change and human activities remain unclear in southwestern China. The normalized difference vegetation index (NDVI) is widely used as a proxy of vegetation production. Here, a breakpoint method was used to better understand the vegetation trend dynamics based on the third generation Global Inventory Monitoring and Modeling System (GIMMS3g) NDVI in southwestern China. Meanwhile, a partial correlation analysis and residual trend (RESTREND) analysis were employed to detect the climatic and anthropogenic drivers behind vegetation dynamics. We found that the trend showed high heterogeneity in space. The annual mean NDVI generally increased at a rate of 0.0011 year−1 from 1982 to 2015, but much of the study area showed an opposite trend before and after the breakpoint. In the western part, the vegetation degraded with a reversal of trend from increase to decrease, where the vegetation types were mainly evergreen needle-leaved and grassland. In contrast, the vegetation increased significantly in the eastern part, showing greening trend regardless of browning or greening trend before the breakpoint. Temperature had a positive correlation with vegetation in the eastern part of the study area, while also had some negative correlations with vegetation in western mountainous areas where surface soils are prone to droughts. Solar radiation had a positive correlation with vegetation in the western part of the study area. Overall, temperature was the dominant climatic factor, and intensified human activities of afforestation and agriculture activities leaded to the strong greening trend. Our findings improved the understanding of long-term changes in vegetation and the roles of climate and anthropogenic activities over southwestern China.

Keywords

• NDVI
• Vegetation dynamics
• Climate
• Human activities
• Breakpoint analysis