Vegetation Dynamics of Restored and Remnant Willamette Valley, OR Prairie Wetlands

Although once common throughout the Willamette Valley of Oregon, USA, prairie wetlands now occupy less than two percent of their historic extent. We compare vegetation trends and spatial patterns in plant community composition for prairie wetlands in the southern Willamette Valley, including four remnants and four restorations, sampled in 2000, 2005, and 2011. Patterns and trajectories of change in species assemblages were evaluated using non-metric multidimensional scaling (NMDS), multi-response permutation procedure (MRPP), native and introduced species diversity, and species accumulation curves. Geographic location was a statistically-significant grouping variable according to MRPP. Within each geographic region, vegetation at restorations has become more similar to that of remnants over time. Remnants have significantly higher native species richness than restorations and NMDS ordination of the data for native species separated remnants from restored sites. Species accumulation curves also revealed different patterns for native and introduced species in remnants compared to restorations. While the vegetation of restorations has become more similar to that of nearby remnants, remnants can still be distinguished from restorations based on the native species assemblages. These results show that, with sustained effort, plant communities in restorations can converge with those in remnant patches, and that it is important to preserve and restore sites in different geographic regions, as different locations may preserve different plant assemblages.