Phenological mismatches between larks and grasshoppers induced by climate change degrade a grassland ecosystem through trophic cascades.

Global climate change has led to phenological mismatches between birds and insects across natural ecosystems. However, their effects on ecosystems remain poorly understood. Here we show whether climate change induced phenological mismatches between birds and insects can degrade grassland ecosystems through trophic cascades. We conduct decadal (2014-2024) phenological surveys of larks (Alaudidae) and grasshoppers (Acrididae) in a grassland nature reserve in Inner Mongolia, China. Significant phenological mismatches between larks and grasshoppers occur within the reserve, and mean temperature in April emerges as the most critical factor influencing mismatch magnitude. The phenological mismatch index, a measure of mismatch between lark hatching and grasshopper nymphal phenology, shows stronger explanatory power for variations in net primary productivity (NPP) within the reserve than climatic factors. The annual NPP decreases as mismatch magnitude increases. Moreover, we conduct a three-year bird exclusion experiment to identify the trophic cascading mechanism linking the phenological mismatch to vegetation productivity. The results demonstrate that a marked increase in grasshopper abundance, induced by the absence of lark predation, results in a decline in plant species diversity, soil degradation, and a reduction in plant aboveground biomass. Our results indicate that climate change induced phenological mismatches between birds and insects can degrade ecosystems through trophic cascades.