Influence of Prescribed Burning on Abundance of Native versus Non-Native Thistles

Neuhart, C. and N. H. Troelstrup, Jr.

Non-native thistles, such as the Canada Thistle, are recognized to have an unfavorable impact on the native vegetation and wildlife community in grassland habitats. There have been efforts to control these invading thistles, such as the use of manual labor, insects, herbicides, and fire. This study examined the effect of prescribed burning on the abundance of native and non-native thistles at the Oak Lake Field Station. Three replicate sampling plots (5m x 5m) were defined within areas most recently burned in 2006, 2005, 2004, 2001, 1998, and 35+ years. Stem counts were made biweekly from late-May until mid-August. In the 2005, 2004, and 2001 treatment areas, there were 0 thistles found throughout the entire summer. For the 2006 plots, the maximum amount of native thistles counted was 2, yet the maximum amount of invasive thistles counted was 39. However, in the 1998 and 35+ years sites, there were extreme amounts of invasive thistles found, reaching up to 171 in a single plot. There were no native thistles counted in these 2 sites. There was a strong correlation between abundance of natives/invasives and years since last prescribed burn. According to the data collected, the amount of invasive thistles increased as the years since last burn increased, with the exception of the 2006 site. The abundance of native thistles was incredibly small compared to the abundance of invasives. As the years since last burn decreased, the amount of natives increased. In conclusion, it was determined that prescribed burning is successful in reducing the abundance of invasive thistles. (Presentation pdf)