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• 1. [Article] The effects of site preparation on native forb establishment in a wet prairie, Willamette Valley, Oregon

  Wetlands and wet prairies are economically and environmentally valuable ecosystems, but many have been degraded or converted to other uses. As human understanding of wetlands' value has increased, restoration ...

  Citation × Citation Citation Abstract Copy Title: The effects of site preparation on native forb establishment in a wet prairie, Willamette Valley, Oregon Author: Norman, Katherine N. Wetlands and wet prairies are economically and environmentally valuable ecosystems, but many have been degraded or converted to other uses. As human understanding of wetlands' value has increased, restoration efforts have grown correspondingly. Restoration attempts use a diversity of methods, which often include seeding with native plant species. This thesis reports on early results from a restoration project that was conducted in the Willamette Valley of western Oregon on a study site that historically supported wet prairie but had been converted to agricultural use. The site was withdrawn from agricultural use 11 – 12 years prior to the work reported here, contoured to reestablish wetland hydrological conditions, and planted with the native perennial, tufted hairgrass (Deschampsia cespitosa), in a preliminary attempt to recreate wet prairie conditions. The subsequent management goal, addressed in the work reported here, was to increase native species richness without increasing exotic plant cover by seeding the site with a mixture of 27 common wetland natives. In each of three blocks at the site, four units were treated either by burning (N = 2 per block) or mowing (N = 2 per block), then seeded with a mixture of 27 common native wetland species. One each of the burned and mowed units from each block was treated with glyphosate herbicide. Thus burning, burning + herbicide, mowing, mowing + herbicide, all with seeding of native species, and an unseeded control each occurred in one unit in each of three blocks at the site. The specific objectives of this study were to determine: 1. If treatments varied in their effects on plant communities, 2. Whether treatments differed in the degree to which they enhanced establishment of seeded species or other native species, 3. If so, which treatment was most effective at increasing cover or richness of native or seeded species, and 4. Consequences of treatments in terms of exotic species cover or richness. Although the low number of replications (N = 3) limited statistical inference, it appeared post-treatment plant communities differed among treatment groups (including controls) (Blocked Multi-Response Permutation Procedure; A-value 0.249 to 0.312; p-value < 0.005). While all four seeding treatments enhanced cover by native species compared to that in controls, burning without herbicide appeared to be particularly effective. Burning and burning + herbicide enhanced cover of seeded species more than did mowing treatments; while all four seeding treatments appeared to increase richness of native species overall, relative to that in unseeded controls, differences were not statistically significant. However, treatments also tended to increase cover and richness of exotic species relative to those in controls. While the increases in exotic species richness post-treatment were generally smaller than the increases in native species richness, changes in cover tended to be similar between the two species groups. Further monitoring of this site will be necessary to determine longer term consequences of these treatments for the plant communities. Title: The effects of site preparation on native forb establishment in a wet prairie, Willamette Valley, Oregon Author: Norman, Katherine N. Wetlands and wet prairies are economically and environmentally valuable ecosystems, but many have been degraded or converted to other uses. As human understanding of wetlands' value has increased, restoration efforts have grown correspondingly. Restoration attempts use a diversity of methods, which often include seeding with native plant species. This thesis reports on early results from a restoration project that was conducted in the Willamette Valley of western Oregon on a study site that historically supported wet prairie but had been converted to agricultural use. The site was withdrawn from agricultural use 11 – 12 years prior to the work reported here, contoured to reestablish wetland hydrological conditions, and planted with the native perennial, tufted hairgrass (Deschampsia cespitosa), in a preliminary attempt to recreate wet prairie conditions. The subsequent management goal, addressed in the work reported here, was to increase native species richness without increasing exotic plant cover by seeding the site with a mixture of 27 common wetland natives. In each of three blocks at the site, four units were treated either by burning (N = 2 per block) or mowing (N = 2 per block), then seeded with a mixture of 27 common native wetland species. One each of the burned and mowed units from each block was treated with glyphosate herbicide. Thus burning, burning + herbicide, mowing, mowing + herbicide, all with seeding of native species, and an unseeded control each occurred in one unit in each of three blocks at the site. The specific objectives of this study were to determine: 1. If treatments varied in their effects on plant communities, 2. Whether treatments differed in the degree to which they enhanced establishment of seeded species or other native species, 3. If so, which treatment was most effective at increasing cover or richness of native or seeded species, and 4. Consequences of treatments in terms of exotic species cover or richness. Although the low number of replications (N = 3) limited statistical inference, it appeared post-treatment plant communities differed among treatment groups (including controls) (Blocked Multi-Response Permutation Procedure; A-value 0.249 to 0.312; p-value < 0.005). While all four seeding treatments enhanced cover by native species compared to that in controls, burning without herbicide appeared to be particularly effective. Burning and burning + herbicide enhanced cover of seeded species more than did mowing treatments; while all four seeding treatments appeared to increase richness of native species overall, relative to that in unseeded controls, differences were not statistically significant. However, treatments also tended to increase cover and richness of exotic species relative to those in controls. While the increases in exotic species richness post-treatment were generally smaller than the increases in native species richness, changes in cover tended to be similar between the two species groups. Further monitoring of this site will be necessary to determine longer term consequences of these treatments for the plant communities. Close

• 2. [Article] Plant community dynamics in remnant and restored Willamette Valley wetland prairies

  Invasion by exotic species can pose a major challenge for developing native plant communities in wetland restoration projects. Often native plant communities do not develop as anticipated in restored wetlands ...

  Citation × Citation Citation Abstract Copy Title: Plant community dynamics in remnant and restored Willamette Valley wetland prairies Author: Schwindt, Rachel A. Invasion by exotic species can pose a major challenge for developing native plant communities in wetland restoration projects. Often native plant communities do not develop as anticipated in restored wetlands due to colonization by exotic species that dominate the native plant community. Despite the time and expense to restore wetlands, there has been little long term research to compare plant communities in restored and natural wetland sites. Research into plant community diversity across several wetland sites over several years can provide a broader perspective into how these ecosystems recover from long-term disturbance. The objective of this study was to compare plant community change from 2000 to 2005 between restored and remnant wetland prairie sites in the southern Willamette Valley in Oregon to determine if exotic species abundance was consistent between these groups. Specific objectives included 1) comparing the diversity and abundance of all species in remnant and restored wetland prairie sites, 2) evaluate the trajectory of community change between remnant and restored wetland prairie sites to determine if there was rapid change in restored sites, and 3) describe the plot level heterogeneity of the plant community in all sites to determine how microsites influence diversity. In 2005, species abundance was re-measured in four remnant wetland prairies and four restored wetland prairies that had been selected for an unrelated vegetation survey in 2000. Species were characterized by life form, origin, and wetland indicator status. Species abundance between groups of remnant and restored sites were compared using a multi-response permutation procedure (MRPP). The plant community trajectory was evaluated with nonmetric multidimensional scaling (NMS) and tested for significance with multivariate analysis of variance (MANOVA). Species area curves were compared between sites and within remnant and restored groups of plots. Within-year and between-year significance tests indicated that remnant and restored sites were similar in exotic species abundance, graminoid abundance, and wetland species abundance with no significant difference between these remnant and restored wetland prairie sites. Individual sites in both groups experienced changes in exotic species abundance which confounded the statistical results. Species heterogeneity was no more spatially diverse across the remnant site plots than restored site plots. Species area curves did not show significant differences between remnant and restored plots but individual plots did show homogeneous community characteristics at smaller spatial scales. Restoration sites had developed high graminoid cover by the 2000 survey which was conducted two to three years after restoration was initiated. All sites were equally likely to contain exotic species. Exotic species common across all sites included Centaurium umbellatum, Holcus lanatus, and Hypericum perforatum. Native species common across sites included Deschampsia cespitosa, Danthonia californica and Juncus tenuis. These results suggested that differences between remnant and restored Willamette Valley wetland prairie sites were not generalizable at the landscape scale and were more dependent on site specific management activities and local barriers to colonization. Five years may not be enough time to see evidence that suggests if restored plant communities will develop spatial characteristics of the remnant sites. This research does suggest that multi-site comparisons help distinguish individual sites that are not developing characteristics of remnant wetland plant communities. Title: Plant community dynamics in remnant and restored Willamette Valley wetland prairies Author: Schwindt, Rachel A. Invasion by exotic species can pose a major challenge for developing native plant communities in wetland restoration projects. Often native plant communities do not develop as anticipated in restored wetlands due to colonization by exotic species that dominate the native plant community. Despite the time and expense to restore wetlands, there has been little long term research to compare plant communities in restored and natural wetland sites. Research into plant community diversity across several wetland sites over several years can provide a broader perspective into how these ecosystems recover from long-term disturbance. The objective of this study was to compare plant community change from 2000 to 2005 between restored and remnant wetland prairie sites in the southern Willamette Valley in Oregon to determine if exotic species abundance was consistent between these groups. Specific objectives included 1) comparing the diversity and abundance of all species in remnant and restored wetland prairie sites, 2) evaluate the trajectory of community change between remnant and restored wetland prairie sites to determine if there was rapid change in restored sites, and 3) describe the plot level heterogeneity of the plant community in all sites to determine how microsites influence diversity. In 2005, species abundance was re-measured in four remnant wetland prairies and four restored wetland prairies that had been selected for an unrelated vegetation survey in 2000. Species were characterized by life form, origin, and wetland indicator status. Species abundance between groups of remnant and restored sites were compared using a multi-response permutation procedure (MRPP). The plant community trajectory was evaluated with nonmetric multidimensional scaling (NMS) and tested for significance with multivariate analysis of variance (MANOVA). Species area curves were compared between sites and within remnant and restored groups of plots. Within-year and between-year significance tests indicated that remnant and restored sites were similar in exotic species abundance, graminoid abundance, and wetland species abundance with no significant difference between these remnant and restored wetland prairie sites. Individual sites in both groups experienced changes in exotic species abundance which confounded the statistical results. Species heterogeneity was no more spatially diverse across the remnant site plots than restored site plots. Species area curves did not show significant differences between remnant and restored plots but individual plots did show homogeneous community characteristics at smaller spatial scales. Restoration sites had developed high graminoid cover by the 2000 survey which was conducted two to three years after restoration was initiated. All sites were equally likely to contain exotic species. Exotic species common across all sites included Centaurium umbellatum, Holcus lanatus, and Hypericum perforatum. Native species common across sites included Deschampsia cespitosa, Danthonia californica and Juncus tenuis. These results suggested that differences between remnant and restored Willamette Valley wetland prairie sites were not generalizable at the landscape scale and were more dependent on site specific management activities and local barriers to colonization. Five years may not be enough time to see evidence that suggests if restored plant communities will develop spatial characteristics of the remnant sites. This research does suggest that multi-site comparisons help distinguish individual sites that are not developing characteristics of remnant wetland plant communities. Close