Multiple community properties drive ecosystem resistance and resilience to extreme climate events across mesic grasslands

Ecosystem resistance and resilience to increasingly more common extreme climate events is impacted by community properties, including biodiversity. However, the relative importance of species richness, evenness, and dominance is debated and is further modulated by global change factors such as nutrient addition. By synthesizing up to four decades of data from three Long-Term Ecological Research sites, we show that resistance and resilience of aboveground biomass to extreme climate events are determined by multiple properties of plant community structure, including species richness, evenness, and dominant species. The influence of these community properties depends on the type of extreme event (dry vs. wet), while nutrient availability alters resistance and resilience indirectly via community properties. Our work builds on the foundational findings of Tilman and Downing (1994), which demonstrated that greater species richness stabilizes productivity during drought. While highly influential, that work has been debated and refined over the past three decades, with growing recognition that other components of plant community structure — particularly the role of dominant species and evenness — determine ecosystem functioning and stability. Our findings support the richness–stability relationship in the case of drought, but they also reveal that dominance plays a stronger role in buffering wet-year responses and that evenness can enhance resilience under certain conditions. In detail, greater species evenness promoted resilience in control, but not nutrient addition plots during dry years. In contrast, greater dominance increased resistance to extreme wet years, with nutrient addition decreasing resistance overall. However, resilience to extreme wet years was negatively affected by the interaction of dominance and nutrient addition, such that greater dominance in nutrient addition plots lowered resilience. Furthermore, nutrient enrichment alters these dynamics indirectly by reshaping these community properties. Species richness and dominance are also directly reduced by extreme climate events, which may erode resistance and resilience to future events. These findings advocate for managing plant communities for community properties beyond species richness to promote resistance and resilience to a future of increasing extreme climate events and global change.