Revealing the dual impacts of climate change and grazing on vegetation in Mongolia: Permafrost buffering and the paradox of greening

Mongolia's ecosystem is highly vulnerable to both climate change and overgrazing, which threaten its ecological stability and livestock husbandry. However, the lack of high-quality data has prevented a thorough investigation into how climate variability and grazing activities jointly affect vegetation growth. Here, we applied long-term satellite time series data, in situ observations, national statistics, and reanalysis data to investigate the annual variations in the spatiotemporal patterns and drivers of vegetation growth from 2000 to 2018 in Mongolia. The relative contributions were qualified to understand how climatic variables (precipitation, air temperature, solar radiation, and wind speed) and livestock density affect vegetation growth via the normalized difference vegetation index (NDVI) as a proxy. Our findings revealed that i) the NDVI exhibited a statistically significant increasing trend of 0.0023 per year (p < 0.05) during the peak growing month of July; ii) the dominant factors controlling vegetation growth included precipitation (53.1%), air temperature (33.9%), solar radiance (4.4%), wind speed (4.6%) and livestock density (4.0%); iii) accounting for the memory effects of vegetation improved the explanatory power of vegetation growth variations; iv) precipitation and air temperature at the onset of the spring growing season were critical for the annually peak vegetation growth; v) permafrost reduced vegetation sensitivity to variations in precipitation and air temperature, thereby extending the duration of vegetation memory; and vi) NDVI greening or apparent stability masked the actual degradation of rangelands. This study not only enhances our understanding of vegetation changes in response to environmental and anthropogenic drivers but also provides a scientific basis for adaptive management strategies in Mongolia.