| Ecological restoration is viewed as a means to accelerate succession to achieve a desired ecosystem, and wetland mitigation policies assume restoration can rapidly and predictably compensate for impacted wetlands. However, restoration success might vary depending on landscape context, which constrains the pace and outcome of succession. I reviewed the progress of 76 mitigation sites in Illinois, USA, from both a policy and an ecological perspective and linked plant community dynamics to broader ecological contexts. Stated goals for these wetlands largely focused on vegetation. Compliance with site-specific performance criteria varied depending on site goals; sites often failed to comply with criteria related to survival of planted vegetation or requirements that dominant species should be native and non-weedy, whereas sites often met criteria for establishment of vegetation cover. Some vegetation-based indicators of restoration progress, especially those based on species richness, achieved levels equivalent to reference sites within five years, whereas others took longer than mitigation wetlands are typically monitored. Indicators based on species composition, in contrast, often increased over the first few years then unexpectedly declined. Wetland plant communities followed expected successional trends; annual species were replaced by clonal perennials, and rates of species gain and turnover declined over time. However, among-site differences in species composition exceeded commonalities based on site age, limiting the ability of practitioners to predict restoration outcomes. The pace of succession was influenced by landscape setting but not site area; urban wetlands underwent succession more slowly than those in agricultural settings. Context also influenced restoration outcome. Species composition was associated with both local- and landscape-scale factors, whereas functional group composition converged in sites with similar local abiotic conditions. The conservation value of wetlands was influenced by regional-scale factors that constrained local environmental conditions. In particular, the number, cover and occurrences of non-native species increased with increasing latitude, urbanization, and/or soil nitrogen. Judgment of site's regulatory compliance depends on the goals that were set for the site and on performance criteria chosen to measure site progress. However, compliance with performance criteria is not necessarily indicative of ecological success, which depends on factors beyond the boundaries of a restoration site. |
