Spatio-temporal changes and driving force analysis of vegetation net primary productivity in Gannan Tibetan Autonomous Prefecture

Since 2003, the Gannan Tibetan Autonomous Prefecture has implemented a series of regional ecological protection policies, including “returning farmland to grass”. The response mechanisms between net primary productivity (NPP) and the normalized difference vegetation index (NDVI), solar radiation, temperature, and precipitation in different vegetation types in Gannan are still unclear. Furthermore, the spatial and temporal characteristics of vegetation NPP and the migration of the center of gravity in the region have not been investigated. In this study, based on MODIS remote sensing, meteorological, and vegetation type data, the Carnegie-Ames-Stanford Approach (CASA) model was used to estimate vegetation NPP in Gannan from 2000 to 2019, analyze the spatial and temporal variation characteristics of NPP, and explore the response relationships between vegetation NPP and NDVI, temperature, precipitation, and solar radiation under different vegetation types. The annual average value of vegetation NPP from 2000 to 2019 was 621.79 g·m⁻², and 96.63% of the area showed an increasing trend. The center of gravity of vegetation NPP from 2000 to 2019 showed an overall northwest to southeast migration, and the growth rate of vegetation NPP in the southeast was higher than that in the northwest. The overall positive relationship between vegetation NPP and temperature, precipitation, and solar radiation was obvious, and the northern edge and the eastern center showed a negative relationship. Finally, the NPP of woodland, scrub, and grassland showed a stable increase, and the temperature of the wetland type also showed a significant increase in addition to NPP. The findings provide theoretical support for the evaluation of ecological quality and implementation of ecological projects.