Wetland restoration: can short-term success criteria predict long-term outcomes?

Worldwide wetland loss over the past 50 years has made wetland conservation a public policy priority, leading to an increase in wetland restoration programs. However, predicting long-term restoration outcomes remains difficult. The monitoring of these programs rarely exceeds 5-10 years, forcing wetland managers to rely on short-term success criteria that may be criticized by the scientific community. Our objective was to assess the significance of four short-term success criteria (Carex ssp. shoot density, Salix ssp. survival, invasive species cover, and hydrologic dissimilarity to reference sites) used in a restoration program of 12 wetlands monitored for 5 years post-restoration in predicting restoration outcomes 15 years post-restoration. We defined the success of restoration efforts after 15 years using a cluster analysis-based approach, and the clusters were described using principal coordinate analysis and Tukey's post hoc honest significant difference test. Finally, we assessed the pertinence of each short-term success criteria in predicting long-term restoration outcomes using Pearson correlation tests and spatial regressive models. Our results demonstrate that stress-based short-term success criteria can be reliable predictors of longer-term success for communities with shallow water tables, whereas target-species-based short-term success criteria are not. Hydrologic dissimilarity to the reference site was appropriate for willow-sedge community outcome predictions, while invasive species cover was best for sedge community outcome predictions. For communities in drier habitats, such as the willow-herb community, none of the tested short-term success criteria were significant predictors of long-term restoration outcomes, and further research is required to identify suitable short-term success criteria.