Persistent greening against drying in northeast Asian semiarid grasslands: Asymmetrical responses of direct and legacy effects to intensified drought

Abstract

Despite experiencing a decadal shift towards drought conditions at the end of the 20th century, semiarid grasslands in northeast Asia (NEA) exhibited an evident greening trend from 1982 to 2020. However, the mechanism behind this phenomenon remains unclear. Hence, we analysed the interdecadal changes in vegetation response to drought on the basis of the standardised precipitation evapotranspiration index (SPEI) and Global Inventory Modelling and Mapping Studies LAI4g datasets, with an emphasis on the differences between direct and legacy effects (as measured by resilience), to explore the mechanism of persistent grassland greening. Results revealed that during the post-drought shift period (2000–2020), the sudden decrease in the water content of the intermediate soil layer triggered an intensified vegetation response to drought. Specifically, although direct effects and resilience were amplified, they exhibited asymmetric changes. Resilience was stronger than direct effects, and this difference increased with increasing drought (drought recovery) levels. These combined effects may account for persistent greening against intensified drying in the semiarid grasslands in NEA. Given the projected exacerbation of future droughts, this study holds notable importance for comprehending the long-term change dynamics of dryland ecosystems.