Abstract
Understanding the relationship of hydrothermal conditions to vegetation changes is conducive to revealing the feedback mechanism connecting climate variations and vegetation. Based on the methods of Theil–Sen median analysis, and the Mann–Kendall trend test, this research investigated the spatiotemporal vegetation dynamics in Central Asia using the Normalized Difference Vegetation Index (NDVI) and grid climate data from 1982 to 2015. Further, the contributions of hydrothermal conditions to vegetation changes were quantified using a boosted regression tree model (BRT). The results demonstrated that the spatiotemporal characteristics of vegetation dynamics exhibited significant differences in different seasons, and most pixels showed increasing trends in the growing season and spring. Boosted regression tree analysis indicated that the contributions of hydrothermal conditions to vegetation dynamics exhibited temporal and spatial heterogeneity. During the annual, growing season, and summer examination periods, the contribution value of the increase in warming conditions (temperature or potential evapotranspiration) to vegetation degradation in the region due to the hydrothermal tradeoff effect (water) was 49.92%, 44.10%, and 44.95%, respectively. Moreover, the increase in warming conditions promoted vegetation growth, with a contribution value of 59.73% in spring. The contribution value of the increase in wetting conditions (precipitation or soil moisture) to vegetation growth was 48.46% in northern Central Asia, but the contribution value of the increase in warming conditions to vegetation degradation was 59.49% in Ustyurt Upland and the Aral Sea basin in autumn. However, the increase in warming conditions facilitated irrigation vegetation growth, with a contribution value of 59.86% in winter. The increasing potential evapotranspiration was the main factor affecting vegetation degradation in the Kyzylkum Desert and Karakum Desert during the annual, growing season, and autumn examination periods. Precipitation and soil moisture played decisive roles in vegetation dynamics in northern Central Asia during the growing season, summer, and autumn. This research provides reference information for ecological restoration in Central Asia.
Highlights
Vegetation, a vital primary product, is a fundamental element of the terrestrial ecosystem [1]
Existing works have found that changes in hydrothermal conditions affect vegetation dynamics by affecting vegetation photosynthesis, respiration, and transpiration [14,15,16]
The region is characterized by a temperate continental climate, with significant regional differences in its hydrothermal conditions, including spatial variance in precipitation, soil moisture, and temperature, all of which decrease from the mountains to the plains and from north to south [29,37,40]
Summary
Vegetation, a vital primary product, is a fundamental element of the terrestrial ecosystem [1]. An increase in moisture can weaken the effects of thermal conditions on vegetation, but too much water can inhibit photosynthesis and lead to vegetation senescence [13]. Against the background of climate warming, hydrothermal conditions in different regions have exhibited significant change, and the impact of climate variations on vegetation dynamics in different regions varies [9,13,17], leading to a complex relationship between hydrothermal actors and vegetation changes. Differences in time and region lead to variable hydrothermal conditions, different vegetation changes, and significant uncertainty in the mechanism relating vegetation dynamics and climate change. Increasing attention is focused on the quantification of the contributions of hydrothermal conditions to vegetation change [18,19,20,21,22,23]
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