The stability of grassland spring phenology to extreme drought is modulated by radiation and biodiversity on the Tibetan Plateau

Long-term trends of vegetation spring phenology (i.e., start of season, SOS) under ongoing climate change have received widespread attention due to its implication for ecosystem carbon balance. However, the stability of SOS under short-term disturbance, such as extreme drought event, remains poorly understood. Here, we assessed the geographic patterns of SOS stability, encompassing multiple components (resistance, resilience, and temporal stability), in response to preseason extreme drought events using satellite-observed vegetation index and gridded drought index across the alpine grasslands of the Tibetan Plateau (TP). Higher resistance and temporal stability of SOS were generally observed in the meadow-dominated eastern TP, with declining westward along longitudinal gradients. Whereas, the resilience of SOS peaked in the semi-arid central plateau. The spatial coherence between resistance and temporal stability suggests that the consistency of SOS during drought periods (i.e., temporal stability) critically depends on its capacity to resist drought (i.e., resistance). The geographical detector model revealed that radiation and biodiversity were the primary drivers of the spatial distributions of SOS resistance and temporal stability, with higher resistance and temporal stability associated with lower radiation and greater biodiversity. In contrast, the contribution of environmental settings to SOS resilience was relatively lower than that of resistance, with a spatial trade-off between resistance and resilience across the TP, except in the western regions, where a distinct low resistance-low resilience pattern was observed. Overall, our findings provide novel insights into ecosystem stability under extreme droughts, and improve the representation of drought responses in alpine ecosystem within land surface models.