Wetland productivity and stability increase more with average plant size than with plant functional diversity.

The functional trait diversity of plant communities regulates the effects of biodiversity on ecosystem functioning and stability. However, the role of functional trait diversity in explaining ecosystem productivity and stability in natural wetlands remains unclear. Using vegetation data from 1139 sites across U.S. wetlands, we examine the associations of functional diversity (trait dispersion within a community) and functional identity (community-level trait values) of plant size traits and resource economics traits with satellite-derived productivity and temporal stability at continental scales. Community-level plant size shows the strongest association with productivity and stability, which is consistent across different wetland types and levels of anthropogenic disturbance. While functional diversity is generally positively correlated with productivity and stability, these relationships vary substantially across environmental contexts. Notably, weaker correlations are observed under higher levels of anthropogenic disturbances. These findings suggest that wetland conservation and restoration efforts should focus on increasing functional diversity and prioritizing large dominant species to increase productivity and stability.