Spatio-temporal variation in and the driving factors of desert vegetation in Xinjiang

Desert vegetation is an important part of arid and semi-arid ecosystems in Xinjiang and plays a key role in the maintenance of ecosystem balance. Timely and accurate monitoring of the temporal and spatial distribution of desert vegetation is important for the sustainable utilization of the resources and ecological restoration. Based on remote sensing technology combined with two Normalized Difference Vegetation Index (NDVI) products (AVHRR-NDVI and MOD13A2-NDVI), the area of desert vegetation in Xinjiang from 1989 to 2017 was estimated. The temporal and spatial characteristics of desert vegetation in three typical river basins (Ulungur River Basin, Aksu River Basin, and Yarkand River Basin) were analyzed, and the relationships between desert vegetation and the climate factors, runoff changes, and policy factors were discussed. The NDVI products were used to calculate the vegetation coverage ( f_c), and the distribution and area of desert vegetation were determined according to the threshold of vegetation coverage. Desert vegetation was determined within the f_c threshold range of 0.1–0.35, where 0.1–0.25 indicates low-coverage desert vegetation and 0.25–0.35 indicates high-coverage desert vegetation. The transformation between desert vegetation and other vegetation types was calculated using the land use transfer matrix to explore the evolution and transformation of desert vegetation in Xinjiang from 1989 to 2017. The driving factors of desert vegetation evolution in the three typical river basins were analyzed using correlation analysis. The results showed that the total area of desert vegetation in Xinjiang significantly increased from 1989 to 2017 at a rate of 30 900 hm²∙a⁻¹. The area of low-coverage desert vegetation significantly increased at a rate of 32 200 hm²∙a⁻¹; whereas the area of high-coverage desert vegetation did not vary, with a multi-year average value of 2 087 100 hm². The area of desert vegetation in northern Xinjiang increased slightly, accounting for 67% of the total area of desert vegetation. This was mainly due to an increase in low-coverage desert vegetation. The area of high-coverage desert vegetation in northern Xinjiang slighly decreased. The desert vegetation area in southern Xinjiang significantly increased. During vegetation transformation, 508 500 hm² of desert vegetation transformed from high to low desert vegetation, 3.4124 million hm² of non-desert vegetation types transformed into desert vegetation, and 1.9125 million hm² of desert vegetation transformed into non-desert vegetation types. This study of typical river basins showed that the area of desert vegetation increased with increasing precipitation. Precipitation was the most important factor affecting the evolution of desert vegetation, followed by runoff and policy factors. The influence of air temperature on desert vegetation varied across regions, and the area of desert vegetation near water increased with increasing temperature.