Spatiotemporal Variations and Driving Forces of Vegetation Productivity in the Northwest Sichuan Ecological Demonstration Zone, China

A comprehensive analysis of the spatiotemporal dynamics and driving mechanisms of vegetation productivity is critical to sustaining ecosystem services and guiding ecological management in ecologically fragile regions experiencing rapid environmental changes. The Northwest Sichuan Ecological Demonstration Zone (NSEDZ), characterized by complex terrain, pronounced ecological vulnerability, and increasing human disturbances, was selected as a representative case. This study used the Global LAnd Surface Satellite Project (GLASS) net primary productivity (NPP) data to analyze spatiotemporal variations of vegetation productivity from 2001 to 2020 through a trend analysis approach. Subsequently, the relative importance of climatic, anthropogenic, and topographic factors on NPP dynamics was quantified using an interpretable machine learning model. The results indicated that a significant improvement was found in the NSEDZ, with an average annual NPP increase of 3.17 g C/(m²·yr). The majority (63.87%) of the NSEDZ region exhibited vegetation improvement, 35.68% remained stable, and only 0.45% experienced degradation. Further analysis of driving factors demonstrated that anthropogenic influences, particularly change rates of grazing intensity and tree coverage, served as the primary drivers for both vegetation improvement (51.58%) and degradation (42.79%). Specifically, ecological restoration areas characterized by increasing tree coverage and decreasing grazing intensity were predominantly associated with vegetation improvement, whereas the opposite areas were associated with vegetation degradation. Climatic drivers, especially the change rate of precipitation, played a predominant role in maintaining vegetation stability, accounting for 48.00% of the total contribution. In terms of topography, elevation exerted a strong influence on NPP, which promoted the vegetation improvement at higher altitudes and increased the vegetation vulnerability in mid- and low-elevation areas. Overall, these findings revealed the spatiotemporal dynamics and drivers of NPP, offering scientific foundations for optimizing ecological barrier protection and construction strategies in the NSEDZ.