Concurrent climate extremes and biological carryover effects dominate severe seasonal reductions in northern vegetation growth

Seasonal vegetation dynamics, including phenology, growth, and senescence, are highly sensitive to divergent climate extremes. In addition to direct climatic impacts, vegetation can play a critical role in mediating inter-seasonal growth responses. Our findings show that cold extremes dominate vegetation reductions in boreal regions across all seasons, whereas in temperate regions, the primary drivers shift from spring cold extremes to summer and autumn droughts or heatwaves. Critically, the pre-season vegetation conditions can propagate forward, and such biological carryover effects lead to prolonged reductions in vegetation activity across multiple seasons. This is particularly evident in semi-arid regions, where more than half of spring vegetation growth extreme anomalies persist into later seasons due to limited recovery capacity. These results highlight the need for climate adaptation and land-management strategies that account not only for immediate climate extremes but also for the cumulative impacts imposed by ecosystem memory.