Invasiveness and Impact of 48 Exotic Plant Species in Native Grasslands
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.
|Quantifying "apparent" impact and distinguishing impact from invasiveness in multispecies plant invasions||(publication)|
Forest Service Partners