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Invasiveness and Impact of 48 Exotic Plant Species in Native Grasslands

Photo of Location of sites in western Montana sampled to determine the invasiveness and impact of 48 exotic plants in the bluebunch wheatgrass habitat type.  USDA Forest ServiceLocation of sites in western Montana sampled to determine the invasiveness and impact of 48 exotic plants in the bluebunch wheatgrass habitat type. USDA Forest ServiceSnapshot : This study quantified and ranked invasiveness and impact for 48 exotic plant species based on surveys over 20,000 square kilometers (12,427 square miles) of grasslands in western Montana. These data provide a valuable tool for managers to determine the relative impacts of invaders for prioritizing exotic plants for control in the bluebunch wheatgrass habitat type.

Principal Investigators(s) :
Pearson, Dean E. Ortega, Yvette K.
Research Location : Montana
Research Station : Rocky Mountain Research Station (RMRS)
Year : 2015
Highlight ID : 830

Summary

Forest Service scientists quantified and ranked invasiveness and impact of 48 exotic plants based on surveys in the bluebunch wheatgrass habitat type in western Montana. Their 31 sites spanned 20,000 square kilometers of grasslands. (Each site was one hectare, or 2.47 acres.) The research results provide valuable data for managers when prioritizing exotic plants for control in the bluebunch wheatgrass habitat type. They calculated invasiveness scores as the product of a species' range (number of plots occupied) and local abundance (mean percent cover per plot). Impacts were measured as reductions in native plant cover associated with increasing abundance of each invader while controlling for the abundance of other exotic plants within the grassland.

An average of 13 exotic species inhabited each grassland, and the average total exotic cover per grassland was 25 percent. Twenty-five percent of the total identified flora was exotic plants. Of the 48 invaders, 11 showed significant impacts on native plants, five of which are classified as noxious weeds by the state of Montana: spotted knapweed, St. John’s wort, Dalmatian toadflax, Canada thistle, and oxeye daisy. The highest impact invader was cheatgrass, which is currently listed as a regulated plant but not a noxious weed in Montana.

These data are specific to the bluebunch wheatgrass habitat type; the same invaders might have greater or lesser impacts in other community types.

Forest Service Partners

External Partners

  • Bitterroot National Forest
  • Bureau of Land Management
  • Confederated Salish and Kootenai Tribes
  • Lee Metcalf National Wildlife Refuge
  • MPG Ranch
  • Missoula Open Space
  • Montana Department of Natural Resources and Conservation
  • Montana Fish, Wildlife and Parks
  • National Bison Range
  • Plum Creek
  • Rimel Ranch

Strategic
Program Areas

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