Forest dynamics and responses to climate changes and human activities in the arid and semiarid regions of the Altai Mountains, China

Abstract Understanding the mechanisms influencing forest changes is crucial for developing effective adaptation strategies to mitigate the impacts of climate change and anthropogenic factors on ecosystems. In this study, we utilized the Theil–Sen median, Mann–Kendall (MK) test, contribution partition, partial least squares (PLS), geodetector, and residual analysis methods to explore the effects of human activities and climate change on forest cover and forest NDVI in the Altai Mountains. For forest cover, the results indicate that both forest management policies and climate change influence changes, with forest management policies being the primary factor. However, the mechanisms vary across different altitude belts. Natural mortality in alpine and subalpine forests, coupled with the promoting effect of climate change, has led to a dynamic equilibrium in forest cover, while human activities and climate change together promote forest cover expansion in the low mountain belt. For the forest NDVI, areas where climate change and human activities jointly increased NDVI growth account for the largest proportion (50.20%) across the six scenarios. Climate change has a wider influence on the NDVI than do human activities, mainly driving NDVI increases (30.28%). In contrast, forest degradation is caused primarily by human activities (19.39%), especially along forest edges. Among the climate factors, precipitation and snowmelt are the main controlling factors. Notably, snowmelt in March and April (SM_34) is the most important water source for forest growth before the growing season. This study offers essential scientific support for forest management and strategic planning in the Altai Mountains.