This paper presents early results on the response of six non-native invasive plant species to eight wildfires on six National Forests (NFs) in the northern Rocky Mountains, USA. Stratified random sampling was used to choose 224 stands based on burn severity, habitat type series, slope steepness, stand height, and stand density. Data for this report are from 219 stands (875 plots) that have repeated measures 1 to 7 years post-fire. Six invasive plant species are abundant enough to analyze for early indications of response to burning. Spotted knapweed occurrence is highest on Douglas-fir and ponderosa pine habitat types on the Bitterroot NF. Canada thistle occurs on most of the sampled wildfires but at low occurrences and percent plot coverage. Bull thistle has rapid increases on the Bitterroot, Flathead, Kootenai, and Malheur NFs, generally with increasing occurrence at higher burn severities, but average percent coverage is low. Orange hawkweed has low occurrences (<5 percent) and never more than 1 percent coverage on a plot. Meadow hawkweed has its highest occurrence on the Bitterroot NF in low burn severities on Douglas-fir and ponderosa pine habitat types. Prickly lettuce is found on most NFs, the highest occurrences being on the Malheur and Panhandle NFs, with increasing occurrence at higher burn severities; however, average percent cover of prickly lettuce is low. Populations of the six species (especially spotted knapweed, bull thistle, and prickly lettuce) need continued monitoring to determine if occurrence and cover continue to change.
Ferguson, Dennis E.; Craig, Christine L. 2010. Response of six non-native invasive plant species to wildfires in the northern Rocky Mountains, USA. Res. Pap. RMRS-RP-78 Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 12 p.