Assessing the health of a novel riparian ecosystem: Long-term, watershed-scale changes in the breeding bird community

Background/Question/Methods

Novel, human-modified ecosystems now dominate the Earth’s terrestrial surface. People depend on these landscapes for reliable ecosystem services, but as islands of remnant habitat shrink, the world’s biodiversity increasingly depends on novel ecosystems as well. Thus, strategies for enhancing the health and function of novel ecosystems could be a win-win for biodiversity conservation and human needs alike. Yet, assessing the health of novel ecosystems remains challenging; by definition they are fundamentally different from undisturbed systems and comparisons to undisturbed systems may be unrealistic. Can novel ecosystems ever be considered healthy? We assessed changes in the health of a novel riparian ecosystem in California’s Central Valley in response to local management efforts. As a terrestrial complement to previously documented shifts in the fish community, we quantified long-term, watershed-scale changes in the density, diversity, structure, and stability of the breeding bird community (n=49 species) and its functional groups, with a focus on riparian-dependent species.

Results/Conclusions

We detected significant increases in the density and stability of the riparian-dependent species group, as well as a significant directional change in the overall breeding bird community structure, reflecting the increasing dominance of riparian-dependent species. These responses echo previously-documented shifts in the fish community toward native species, and provide evidence for improvements in the health of the entire ecosystem. However, the growth of the riparian-dependent species group stems primarily from increases in common species, while uncommon species remain uncommon, particularly the migratory species; the diversity of the riparian-dependent group did not change. We also identified functional groups that have not responded to management, indicating ecosystem attributes that may require additional attention. Our results suggest there are still important missing components, and that this ecosystem may not yet be ‘healthy.’ Our approach provides detailed information invaluable to conservation and management, particularly in a novel ecosystem framework.