Skip to main content
U.S. flag

An official website of the United States government

Spotted knapweed (Centaurea biebersteinii DC) response to forest wildfires on the Bitterroot National Forest, Montana

Formally Refereed

Abstract

The 2000 Bitterroot wildfires in Montana burned 124,250 ha of forest and rangelands on the Bitterroot National Forest. Because spotted knapweed (Centaurea biebersteinii DC) is common on the Bitterroot National Forest, there is a high potential of expanded knapweed populations following the wildfires. A stratified random sample was used to study forest vegetation development following the wildfires. A total of 283 plots in 71 stands were measured three times during the 5-year period after burning. Knapweed occurred on 19.4% of plots at 1 or 2 years postfire, 26.1% at 3 years, and 37.1% at 5 years. Occurrence at 5 years was higher on Douglas-fir [Pseudotsuga menziesii var. glauca (Beissn.) Franco] habitat types (56.0%) than on subalpine fir [Abies lasiocarpa (Hook.) Nutt.] habitat types (9.6%). Initially after the fire, occurrence and cover of knapweed were inversely correlated with forest floor burn severity; however, the rate of increase over time was higher at higher burn severities. Knapweed cover declined over time on plots with low burn severity and increased over time on plots with high burn severity. Knapweed was tallest on plots where it first occurred at year 3 and shortest where it first occurred at year 5. Collectively, these results suggest that vegetation recovery is important for reducing knapweed populations, especially on Douglas-fir habitat types.

Keywords

spotted knapweed, Centaurea biebersteinii DC, Bitterroot National Forest, wildfire, Douglas-fir, Pseudotsuga menziesii

Citation

Ferguson, Dennis E.; Craig, Christine L.; Schneider, Kate Zoe. 2007. Spotted knapweed (Centaurea biebersteinii DC) response to forest wildfires on the Bitterroot National Forest, Montana. Northwest Science. 81(2): 138-146.
https://www.fs.usda.gov/research/treesearch/61142