Effect of fire, herbicide, and mowing on invasive smooth brome grass and re-establishment of a sand prairie

Background/Question/Methods Control of invasive species is essential for the success of any restoration project.  Smooth brome (Bromus inermis) is a grass native to Eurasia that is now nearly ubiquitous in North America and is frequently encountered in sites targeted for prairie restoration.  However, the lack of published information comparing the success of control methods leaves land managers to rely on word of mouth and anecdotal evidence for decision-making.  To help fill this void, we are studying the efficacy of fire, herbicide (2% glyphosate), mowing, and a fire + herbicide combination for controlling smooth brome and re-establishing a sand prairie community in southwestern Wisconsin.  Seven treatments (two frequencies each of fire, herbicide and mowing, and a single combination), a seed only control and full control were replicated 8 times in a randomized block design (2m x 2m plots). Plot treatments were applied in May and June and all but full control plots were seeded with a 21-species seed mix appropriate to the site in early July.  We utilized both qualitative (Daubenmire cover) and quantitative (point frame) sampling methods to compare the effectiveness of the treatments.  Light availability and litter depth data were also collected. Results/Conclusions The first fall following treatment, Smooth brome cover was reduced significantly by all control methods, but more so by the herbicide and combination treatments.  Light availability at ground level was significantly higher in herbicide and combination plots compared to all others.  By the end of the third growing season following treatment, brome cover remained low in the herbicide and combination plots, but had recovered in the remaining treatment plots and was not significantly different from the controls.  Seeded species had become established in 45 of the 56 treated and seeded plots, but presence of seeded species was significantly greater than the seeded control only in the combination plots. Although other problematic exotic species were present, they did not appear to increase in abundance during the study period. During the first year of restoration, herbicide, either alone or in combination with fire, appears to be the most successful method for control of smooth brome. The combination treatment may be the most beneficial for initial prairie development, perhaps as the result of both increased light availability and decreased litter depth. Although closely spaced repeat treatments (years 1 and 2) did not yield significantly different results, follow-up treatments may be necessary in the long-term to achieve reduced brome cover.