Altitude weakens the drought resistance-resilience tradeoff across northern ecosystems

Abstract

Ecosystem stability during droughts determined by two key attributes: resistance and resilience, which often exhibit a tradeoff across species to biome scales. However, under extreme environmental stress, ecosystems may activate multidimensional stabilization mechanisms that weaken this tradeoff. In this study, we hypothesize that high-altitude ecosystems, shaped by greater climatic heterogeneity and harsher abiotic constraints, display a weaker resistance–resilience tradeoff compared to lowland systems. Focusing on northern terrestrial ecosystems (≥ 30° N), we integrate drought indices with eddy covariance data and remote sensing observations to map the spatial patterns of drought resistance, resilience, and their tradeoffs. Our analysis confirms that the resistance–resilience tradeoff is widespread, yet weakens with increasing altitude. Using explainable machine learning, we identify altitude as the dominant driver of spatial variability in tradeoff strength. Crucially, this effect is biome-dependent: in arid biomes (shrublands, savannas, and grasslands), altitude is a key predictor, whereas in humid biomes (forests and wetlands), climatic variables play a stronger role. Aridity-gradient analysis further reveals that altitude's explanatory power declines in wetter environments. For nearly all biomes, with the exception of wetlands, the resistance–resilience tradeoff weakens with increasing altitude. Finally, Earth System Models (ESMs) from the CMIP6 ensemble fail to capture this altitudinal variability, limiting their predictive accuracy. Our findings highlight the critical role of altitude-driven stability dynamics in shaping drought responses.