Alterations in plant community composition under global change are expected to have consequences for ecosystem function. Importantly, as ecologists we must move beyond metrics of plant communities that only consider changes in species number (i.e., richness), to also incorporate changes in species abundances and identities. The hierarchical response framework predicts that community change will occur in stages, starting with changes in evenness and species reordering, followed by species losses and gains. The framework further suggests that these hierarchical community responses can be linked to hierarchical ecosystem responses to global change drivers. We aim to scale findings from 106 global change experiments to the macro-scale through synthesis of the Community Responses to Resource Experiments (CoRRE) database. We separate our analysis into two components: (1) examining changes in evenness, species rank order, species losses, and species gains with experimental global change manipulation treatments; and (2) linking these community responses to changes in aboveground net primary productivity (ANPP), a critical ecosystem function.
Results/Conclusions
Within individual experiments, community responses to global change treatments varied. Overall, significant changes in plant community composition, as measured by Bray-Curtis dissimilarity between treatment and control plots, were observed at the macroscale. However, the underlying community changes that drove these overall trends were inconsistent across experiments. While changes in species evenness, reordering, losses, and gains in response to global change treatments were observed in many experiments, no general trend emerged at the macro-scale. Further, there was no consistent ordering to the community changes across all sites, in contrast to predictions from the Hierarchical Response Framework. Linking the community responses to global change treatments to corresponding shifts in ANPP revealed that initial ANPP responses to the global change drivers (i.e., physiological response of existing individuals to alterations in resource availability) were later either increased or dampened following community change. Overall, our results illustrate the importance of examining plant community changes when forecasting ecosystem responses to global change across broad spatial scales.