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Contact Information: Wetlands Program Supervisor
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Contact Information:
Trevor Taylor
Wetlands Program Supervisor
City of Eugene, Public Works,
Parks and Open Space Division
1820 Roosevelt Blvd.
Eugene, OR 97402
Phone: (541) 682-4888 |
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Wetlands Research snapshots
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Research-Title
Research in the West Eugene Wetlands
The West Eugene Wetland (WEW) Partnership and the University of Oregon have completed a three-year study that looked at the effectiveness of various wetland prairie restoration site preparation techniques. This study was funded through an EPA Wetland Program Development Program grant with matching funds provided by the City of Eugene. Lane Council of Governments (LCOG) managed the grant for the WEW Partnership, working with a consultant team from the University of Oregon including Scott Bridgham, Bitty Roy, Bart Johnson, and Laurel Pfeifer-Meister. The goal of this research was to provide new information on the effectiveness of various site preparation techniques, not only for the WEW Partners, but also for wetland prairie practitioners throughout the Willamette Valley and elsewhere in the nation. The final report for this study was completed in November 2007, and the research approach and findings are summarized below.
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Testing the Effectiveness of Various Site Preparation Techniques for Wetland Prairie Restoration 
Many recent studies and ecological assessments have identified the protection and restoration of wetland and upland prairies in the Willamette Valley as a high conservation priority (Taft and Haig 2003, Schultz et al. 1993, Wilson et al. 2003, U.S. Fish and Wildlife Service 2003, Defenders of Wildlife 1998, Wilson et al. 1995, Christy and Alverson 1994). This is in large part due to the habitat’s significant decline in acreage, as well as the large number of rare plant and animal species found in these prairie systems. The restoration and protection of wetland prairie has long been a primary goal of the WEW Partnership. Several hundred acres of wetland prairie restoration and enhancement have been achieved, are underway, or are planned for the near future. Despite the relative success of the wetland prairie restoration and enhancement over the past ten years, the WEW Partnership is determined to improve upon its mitigation practices and performance and to communicate that knowledge to the larger wetland restoration community.
 The Importance of Site Preparation
The experience of the WEW Partnership, as well as other restoration practitioners throughout the country, suggests that the method of site preparation is among the most important factors for determining the ultimate success of a restoration project. Successful restoration almost always requires first preparing a site by eliminating non-native plant species so that native species can become established. This is a tremendous challenge in the west Eugene wetlands, since non-native, rhizomatous plants with extensive seed banks (e.g., reed canary-grass [Phalaris arundinacea], meadow foxtail [Alopecurus pratensis], annual ryegrass [Lolium multiflorum], pennyroyal [Mentha pulegium], bentgrass [Agrostis capillaris], and tall fescue [Festuca arundinacea]), are common on most of the sites where upcoming WEW Partner restoration activities will occur.
Many different site preparation techniques have been tried by the WEW Partners and other restoration practitioners throughout the country. A literature review conducted for this study by Greg Fitzatrick of The Nature Conservancy (2004) titled Enhancement Techniques for Restoring Upland and Wetland Prairies in the Midwest the West Coast Regions of North America (see link below) has documented the advantages and disadvantages of many of these techniques. Combinations of techniques, or repeated applications of individual techniques, are often used on a particular site prior to reintroducing native plant species. Some of the techniques, used singly or in combination, that have been tried in Willamette Valley wetland prairie include: (a) disking and tilling, (b) hydrological modifications, (c) herbicides, (d) prescribed fire, (e) thermal weed control, (f) mowing, (g) solarization, (h) removal of fill placed on top of wetlands, and (i) sod and soil removal. Through a decade of implementing wetland restoration projects and monitoring them over time, the WEW Partners have gained a tremendous understanding of the pros and cons of many techniques, especially with regard to their effects on subsequent plant community composition. An analysis of the relative success of these techniques has been documented by Jean Jancaitis of the City of Eugene in Effectiveness of Site Preparation Techniques Used During 10 Years of Wet Prairie Restoration (2004, see link below). Even with the relative success of wetland prairie restoration projects conducted in recent years, the WEW Partners seek to improve the overall quality of such efforts. Wetlands provide a variety of ecosystem services and functions on the landscape in addition to the enhancement of native plant and animal species. To help provide this broader ecosystem perspective, this project examined the effects of the treatments on additional response variables, such as plant productivity, functional soil ecosystem attributes including carbon and nutrient cycling, and soil physical and chemical properties.
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Identifying Site Preparation Techniques to be Included in the Experiment
In support of this study, Lane Council of Governments facilitated a half-day Wetland Restoration Site Preparation Forum [See links at left] held on January 22, 2004 . Approximately 50 people representing a wide array of expertise participated in the forum including soil scientists, farmers, botanists, extension agents, natural resource maintenance workers, landscape architects, and wetland restoration ecologists. The purpose of the forum was to allow participants to share information on the effectiveness of various site preparation techniques they have had experience with, and to identify the most promising techniques to be considered for inclusion in the upcoming experiments. As part of the forum, participant were split into several small groups and asked to develop a set of recommended wetland prairie restoration site preparation techniques in response to two site scenarios (an unmanaged pasture and a tall fescue field). The forum results were then used to develop the experimental design.
 Experimental Design
Based on the results of the Site Preparation Forum and previous experience of the WEW Partners, a total of ten site preparation treatments were selected for the experiment. They included various combinations of tilling, herbicide application, solarization, and thermal weed control. Each treatment was replicated five times, resulting in a total of 50 experimental plots. The plots measured 15 by 15 meters and were separated by 10-meter mowed buffer strips. The relatively large size of the experimental plots was necessary so that typical large agricultural equipment could be used to implement the treatments.
A 4.5-hectare site west of Eugene near Coyote Creek was selected for implementation of the experiment. This site was in agricultural use for annual ryegrass (Lolium multiflorum) production until the spring of 2004. Based on interpretation of the Soil Survey of Lane County (SCS 1987) and historic vegetation mapping (Christy et al. 1999 based on the General Land Office surveys of the 1850s), the site was most likely historically dominated by a wetland prairie plant community. The soil type is mapped as Natroy silty clay loam. Farming of the site did not involve hydrological alterations, and it was seasonally inundated with approximately 5-8 cm of standing water, which is excellent wetland prairie hydrology. Site preparation was conducted between May and October 2004 and included the following techniques in various combinations:
Solarizaton: This technique involved placing a layer of 6 mil. clear plastic over the entire plot beginning in mid-July. A trench was dug around the perimeter to bury the edges of the plastic and create a tighter seal. The plastic was then removed in early October.
Tilling: This involved making two passes over the plots with a large field disk in alternating directions as soon as the soil was sufficiently dry (late June). This was followed by another round of tilling about two weeks later to further break up the soil and vegetation, this  time using a harrow and culti-mulcher.
Thermal: A tractor pulled propane burner (Sunburst) was pulled in a single pass over the test plots to burn off vegetation and seed near the soil surface in mid-July.
Herbicide Application: This involved spraying the test plots with glyphosate (roundup). A first treatment was applied in mid-July, with a second follow-up treatment in early October after the seed bank germinated.
The plots were planted with a broadcast seeder on October 28, 2004 with a wetland prairie seed mix consisting of 15 species of native grasses and forbs.
Experiment Implementation and Data Collection
Three years of post-treatment data has been collected in each of the 50 experimental plots to assess how the various site preparation techniques impact the following four categories of response variables:
· the establishment of native Willamette Valley wetland plants relative to non-native plants;
· the aboveground and belowground productivity of the vegetation;
· the functional soil ecosystem attributes, including nitrogen, phosphorus, and carbon cycling rates, and
microbial biomass and respiration; and
· the physical and chemical properties of the soil.
In addition to the replicated field experiment, the University of Oregon team collected data from three reference sites (high-quality wetland prairie) and performed a retroactive analysis of previous restoration sites. The WEW Partnership has conducted wetland restoration projects on approximately 350 acres of land over the past ten years using various site preparation techniques.
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Summary of Key Findings from Replicated Field Experiment
- Solarization and the fall herbicide application were the most effective treatments for decreasing the seed bank and exotic cover initially. However, over time all treatments had low exotic cover because Lolium multiflorum was not a dominant competitor over time. If the site chosen had a dominant exotic competitor, the outcome would likely be different.
- The solarization treatment gave high native plant cover in the first year and low exotic plant cover throughout the experiment, but this treatment also had low native and overall species richness and diversity. Thus, there was a trade-off between high abundance of competitive native bunch grasses and species diversity in this treatment.
- The July herbicide application had no detectable effect on plant communities.
 If the herbicide could have been applied earlier in the growing season, it may have had a greater effect.
- The tilling treatment, which disturbs the soil and brings up the seed bank, yielded the poorest results in terms of decreasing the seed bank and exotic cover. To be effective, at a minimum it would need to be applied over multiple growing seasons.
- The thermal treatment is advertised as being able to kill all seeds over several centimeter’s depth in the soil, but in this experiment it did not decrease the seed bank. Instead, it acted more like a surface fire and was very effective at killing small seedlings. To reduce the seed bank, this technique would need to be applied at time of seed germination.
- In general, none of the treatments resulted in significant change in the belowground responses after the first year, but as changes in plant composition and productivity feedback to the soil, differences are expected to become larger.
- Herbicide application had no detectable effect on soil variables measured.
- Although treatments had minimal effects on belowground responses, the soils were distinctly different from the annual ryegrass farm field, with soil characteristics becoming more similar to the reference sites.
Ecological Lessons Learned
It is important to take the ecological lessons learned from experiments such as ours so that they can be employed in other restorations. Some key findings were:
- Plant community structure converged among treatments and became more similar to the reference sites over time due to a reduction in the cover of Lolium multiflorum, a loss of early successional species (including those which were planted), and increasing dominance of perennial grasses. Thus, an understanding the successional dynamics of the plant species involved can be used to more quickly direct wetland restorations to a desired plant community condition.
- As a result of these successional dynamics, there was a decrease in overall and native plant species diversity over time in all treatments. Treatment plots never attained the overall or native plant diversity of the reference sites, despite the relatively high cover of exotic plant species in the reference sites.
- A trade-off was evident between native plant cover and diversity. These results suggest that future research efforts need to be focused on establishing and maintaining native plant diversity in wetland restorations.
Summary of Key Findings from Retroactive Study
- Plant communities and soil properties are distinctively different among treatments. Plant community structure in the restored sites remains very different than in the reference sites.
- Reference sites had higher productivity, species richness, and in particular, exotic richness and cover than sod removal or solarization.
- Solarization sites had low richness and productivity (mostly grass), but high total cover. Soils approached reference conditions for most attributes except ecosystem respiration and PO43- availability, perhaps due to the high thatch cover.
- Sod removal sites had low species richness and cover, but similar native species richness and native cover to the reference sites. Soils had dramatically different functional, chemical, and physical properties when compared to reference sites.
- A tradeoff exists between native cover and diversity. It is important to keep this in mind when considering the factors for a ‘successful’ restoration.
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