Predicting the effects of climate change on plant populations will require understanding the relative importance of climate and competition in regulating population dynamics. We used three decades worth of observational data from both Idaho and Kansas to assess the role of climate and competition in determining temporal variation in the abundance of shrub-steppe and grassland species. We addressed three questions. First, do climate or competition variables better explain population dynamics? Second, are species' responses to climate and competition variables explained by plant functional type or lifespan? Third, what are the most important climate and competition variables?

Results/Conclusions

We found that most species responded more strongly to climate than competition, though for some species competition variables were better predictors than climate variables. Variation in species' responses were linked to lifespan and functional type. The shortest-lived species were most affected by climate. In particular, all annual forbs responded negatively to precipitation in the previous year. C4 grasses responded negatively to competition with other grasses. Our work suggests that predicting population dynamics under climate change will require consideration of interspecific interactions, especially for long-lived species.