Spatiotemporal transition of institutional and socioeconomic impacts on vegetation productivity in Central Asia over last three decades.

Central Asia experienced substantial institutional and socioeconomic changes during the last few decades, especially the Soviet Union collapse in 1991. It remains unclear how these profound changes impacted vegetation productivity across space and time. This study used the satellite-derived normalized difference vegetation index (NDVI) and gridded climate data to examine the institutional and socioeconomic impacts on vegetation productivity in Central Asia in 1982-2015. The improved Residual Trend (ResTREND) algorithm was used to calculate NDVI residuals (NDVI) that reflect the impacts of human factors by excluding the influences of multiple climate factors. Our results showed that 45.7% of the vegetated areas experienced significant transitions (p < 0.05) in NDVI with turning point (TP), of which 83.8% occurred after 1992 except for the Aral Sea Basin. During the pre-TP period, positive NDVI (i.e., positive impact) and increasing trends (i.e., positive tendency) were predominant, accounting for 31.6% and 16.5% of the vegetated land, respectively. This was attribute to the expanded cultivation due to Virgin Lands Campaign in North Kazakhstan region and the Amu Darya and Syr Darya Basins. However, the institutional and socioeconomic changes largely suppressed vegetation productivity. In the post-TP period, only 7.0% of the vegetated lands experienced an increasing trend in NDVI, while NDVI decline accounted for 20.1% of the vegetated areas (p < 0.05), mainly distributed in northern Kazakhstan and large areas in the Amu Darya and Syr Darya Basins. Positive transitions resulted from the changes in crop types, decreases in grazing pressure, and increases in water resources, whereas negative transitions were coincident with areas that saw land abandonment, water resource shortages, and soil salinization due to former intensive cultivation. These findings highlight the spatiotemporal changes of institutional and socioeconomic impacts on vegetation productivity in Central Asian dryland and provide implications for future dryland management and restoration efforts.