Response of forest belt on the south slope of Tianshan Mountains in China to global warming during 1990–2020

Mountain vegetation is highly sensitive to changes in climate. Currently, there is no consensus regarding the direction and magnitude of the spatial migration of mountain vegetation in response to climate change. Past studies have reported that climate change promotes upward or downward movement of plant species along an altitude gradient. Based on meteorological data and remote sensing images, this study analyzed the spatial distribution and dynamic trend of mountain altitudinal vegetation belts on the southern slope of the Tianshan Mountains over the past 30 years and discussed the climatic driving factors of these changes. The results showed that the forest belt in this area is unusual because it is embedded in the grassland belt in a patch-like manner and shows discontinuous changes or replacements along the vertical gradient. With the coexistence of warm humidification and warm drying on the southern slope of the Tianshan Mountains, the response of the upper and lower altitudes of the forest belt to climate change was similar, showing a trend of migration to higher-altitude areas. The main climatic factors affecting the migration of the upper and lower altitudes varied spatially. In general, the upper limit of the forest belt had a higher association with precipitation during the vegetative growth season, while the contribution of temperature-related factors to the lower limit of the forest belt was greater.