Elevation dependence of drought legacy effects on vegetation greenness over the Tibetan Plateau

摘要

Extreme drought events exert both immediate and prolonged influences on terrestrial ecosystems, yet the patterns and mechanisms of the delayed effects of extreme drought on alpine ecosystems remain largely unknown. In this study, we use satellite-derived normalized difference vegetation index (NDVI) data to examine the legacy effect of severe drought events on vegetation greenness across the Tibetan Plateau (TP). A pervasive, negative drought legacy effect, lasting about one year, is detected for all plant functional types including forests, shrubs and grasslands on the TP. The magnitude of the identified legacy effect, namely, the reduced growing-season NDVI in the first year post-drought, is spatially heterogeneous and exhibits a clear altitude dependence, while divergent relationships between elevation and the legacy effect are observed between alpine meadow and steppe. For alpine meadow, more pronounced legacy effects occur at higher altitudes with lower precipitation and temperature, suggesting a weaker drought resilience of alpine meadow under dryer and colder conditions. Whereas for alpine steppe, the magnitude of the negative legacies reduces as precipitation decreases along the elevation, which might be due to a greater adaptability to drought under more arid conditions that enables plant communities to recover to their normal state faster in these very dry regions. Our results advance the understanding of drought legacy effects on TP alpine ecosystems and highlight future avenues for research into how different alpine ecosystem types will respond to drought stress.