Relationships between flowering phenology and community composition in an experimental restoration of northwest prairies

Abstract Phenology, the timing of biological life cycles, is a key indicator of global climatic change, with numerous studies showing that species' phenologies are shifting in response to climate change. Despite general trends (e.g., warming causing earlier arrival of spring events such as leaf‐out and flowering onset), studies repeatedly reveal that phenological changes tend to be species‐specific and thus may alter species interactions. Less‐studied is the potential feedback between biotic interactions and phenology and the impacts on species' fitness. To understand the consequences of shifting phenology for species and communities, we need to quantify how phenology and competition interact to affect species' fitness. Here, we studied the potentially interacting effects of species' phenology and competition on plant fecundity (as a proxy for fitness). We sowed seeds of various species combinations to test how variation in competitor species richness, identities, and densities affect the phenology and fecundity of an annual wildflower, Clarkia purpurea . We found that C. purpurea 's flowering phenology varied with competitor identity and competitor species richness, that fecundity was negatively correlated with competitor density but not species richness, and that the strength of competition tended to vary by competitor identity, but appeared unrelated to the relative phenology of the competitor. These findings offer unique evidence that competitive interactions may impact plant phenology and fecundity in complex ways and could influence species' persistence and coexistence conditions in our changing global environment.