Plant Community Recovery following Restoration in Temporally Variable Riparian Wetlands

Wetlands historically provided many ecosystem services but most have been lost or degraded through land conversion. Recent appreciation for wetland values and increasing ecotourism in the Central Platte River Valley (U.S.A.) has promoted restoration of wet meadow systems, although recovery patterns are not well known. We quantified plant community structure in sloughs (deeper habitats) and adjacent margins (slightly higher elevation) of six wetland sites, restored for 1–7 years at the onset of a 3-year study, and three natural wetlands to assess recovery dynamics. Plant community metrics recovered differentially between habitats. Within restored margins, richness and diversity showed a weak quadratic response with time since restoration, indicating that both indexes overshoot natural levels shortly following restoration. Within sloughs, richness and diversity showed no change with time, suggesting that recovery occurs more quickly in these deeper, moister habitats. Percent similarity of plant communities in restorations and natural wetlands increased linearly over time. However, ordinations of plant community composition showed that recovery was strongly influenced by site-specific hydrology and that recovery may not be a linear trajectory toward natural systems. The analysis and interpretation of plant community dynamics revealed several challenges to restoration assessment, including the role of interannual variability in precipitation, limitations to hydrologic recovery, and temporal variability in plant community structure in natural systems that resulted in “moving targets” for recovery comparisons. Temporal variability in climate must be considered when assessing restoration success in systems where plant community structure is responsive to variable moisture regimes.