Regional Strategies for Restoring Native Prairies

A multi-site, long-term, collaborative research project funded by the Priscilla Bullit Collins Trust of The Nature Conservancy

Principal Investigators: Tom Kaye, Institute for Applied Ecology;
Peter Dunwiddie, The Nature Conservancy

Project Director: Amanda Stanley, Institute for Applied Ecology

Want more information or would like to get involved? Email Amanda!

Summary

Invasive plants, especially non-native perennial grasses, pose one of the most critical threats to protected prairies in the Willamette/Puget/Georgia ecoregion. These prairies are among the most endangered ecosystems in North America, and support many imperiled species. Invasive species reduce native diversity and alter vegetation structure, fire regimes, soil characteristics, and faunal diversity. Our current knowledge regarding the effectiveness of techniques for controlling many herbaceous invasives, especially in sites that retain a significant component of native vegetation, is largely anecdotal or based on results from only a few site-specific studies.

Progress has been hampered by several problems. Funding for prairie restoration has been directed primarily towards on-the-ground actions, with very little devoted to developing the scientific understanding that underpins successful adaptive management. Most studies have been of relatively short duration, and involve only single treatments. Few have employed combinations of treatments, an approach that is likely to produce more effective, synergistic effects, as suggested by results from studies in other systems. We have examined these approaches in a comprehensive manner across a geographic range of sites, and over a time period sufficient to evaluate longer-term system restoration. Our project is designed to address these issues using a comprehensive, multi-site collaboration of scientists and land managers.

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Research Objectives

• Evaluate and improve strategies for controlling the abundance of invasive non-native herbaceous weeds, while maintaining or enhancing the abundance and diversity of native plant species.

• Develop an approach to generalize these results so that they can be applied by land managers engaged in prairie stewardship throughout the region.

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Research Approach

At 11 sites in prairie habitats in Oregon, Washington, and British Columbia (see Research Sites, below), we have identical experimental blocks to test different restoration methods.  Experiments began in 2005 and are planned through 2010. Each block consists of twenty 5 x 5 meter plots: 4 replicates of each of 5 treatments combinations.  Each plot is split in half and native seed was added to one half in fall 2006.  In addition to these small replicated experiments, at many of the sites we also have a larger, unreplicated treatment area (typically 100 x 100 meters) to test how one specific treatment combination works at larger scales. 

Our treatment combinations were developed at a workshop at the start of the study in 2005 which included managers and scientists.  The treatments include combinations of Poast, a grass-specific herbicide, to reduce dominant exotic grasses; spring or fall mowing, to reduce thatch, and reduce seed production and stored reserves of exotic grasses; burning, to reduce thatch and moss and prepare seed-beds for germination; and post-burn application of glyphosate (a broad-spectrum herbicide), to reduce broad-leaf weeds that typically resprout quickly after fire.  The five treatments are:

Native seed was added in the fall/winter of 2006 after the burn and glyphosate treatment to one half of each plot, including controls.  Native species added were Festuca roemeri, Danthonia spicata or californica, Achillea millefolium, Eriophyllum lanatum, Lomatium utriculatum or nudicaule, Plectritis congesta, and Ranunculus occidentalis.

Data on plant communities (percent cover of all vascular plant species) is collected every spring.  Other data collected include soil nutrients, soil moisture, plant biomass, and light interception.

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Research Sites

Our research is conducted at 11 sites in Oregon, Washington, and British Columbia. All sites are generally categorized as upland prairie or oak savannah in the Willamette Valley/Puget Trough/Georgia Basin Ecoregion. Our research plots are found at:

• Pigeon Butte, Finley Wildlife Refuge, OR (USFWS)
• Bellfountain Road, Finley Wildlife Refuge, OR (USFWS)
• Ft. Hoskins, OR (Benton County)
• Scatter creek, WA (WDFW)
• Mima mounds, WA (WDNR)
• Glacial Heritage, WA (WDNR)
• Morgan Property, WA (TNC)
• South Weir Prairie, Ft. Lewis, WA (US Army)
• Triangle Prairie, Ft. Lewis, WA (US Army)
• Smith Priaire, Whidbey Island, WA (AuSable Institute)
• Cowichan Preserve, BC, Canada (Nature Conservancy of Canada)

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Collaborators and Partners

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