Seasonal prescribed burning impacts to northern Minnesota lowland brush ecosystem plant communities

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Seasonal prescribed burning impacts to northern Minnesota lowland brush ecosystem plant communities

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Minnesota lowland brush ecosystems provide critical habitat for wide variety of wildlife including over 80 Species of Greatest Conservation Need. These ecosystems depend on fire disturbance to inhibit woody plant encroachment and maintain the herbaceous plant community. Without fire, woody plants become dominant in the overstory, reduce herbaceous cover, and reduce the quality of habitat for wildlife that rely on spatial and structural diversity. Natural resource managers use prescribed burning to decrease woody plant density and enhance the herbaceous plant community in these ecosystems. Currently, the prescribed fire regime in lowland brush ecosystems is largely limited to the spring season, and research in other ecosystems has found that burn season can result in a wide range of impacts to burn severity and both woody and herbaceous plant communities. Understanding the impacts of burn season is critical for natural resource managers to effectively conduct prescribed burns to meet their management objectives. However, little research currently exists on the impacts of fire in lowland brush ecosystems, let alone burn season. The objective of our study was to determine whether season of prescribed burning led to significant differences in burn severity, changes in total woody plant density, changes in density of common woody species, and changes in herbaceous cover. In 2016, we established permanent sample plots at 4 study sites throughout northern Minnesota in order to monitor burn severity and response of vegetation. Each site was broken into 4 burn units including a spring, summer, fall, and a control where no burn was conducted. The results of this study focused on the impacts of burn season on burn severity and the plant community in the first growing season after the burns were conducted, and includes the results of four spring burns, two fall burns, and two summer burns. While we found that burn severity and plant community response differed among burn season treatments, our findings varied by spatial scale. Burns conducted in the spring burned more area those in fall or summer. Given that more area burned in spring compared to fall or summer, we examined the impacts of burn season at different scales to consider broad landscape scale impacts (burn unit scale) and direct fire impacts (plot scale). Burn unit scale included analysis of all permanent sample plots within each burn unit regardless of whether there was evidence of fire at the plot, and at the plot scale we included only on sample plots where evidence of fire was present. Additionally, we broke down the direct fire impacts at the plot scale to look at impacts on common woody plant species and species groups. At the burn unit scale, spring burns were the most severe, resulted in the highest amounts of topkilled woody stems, and the overall greatest reduction in woody plant density even though vigorous resprouting was likely occurring. At the plot scale, burn severity did not differ among burn seasons, but spring burns still resulted in an overall reduction in woody stems while fall and summer burns did not. Furthermore, woody species varied in their response to burn season with some species appearing to resprout prolifically and others not as much, while herbaceous cover did not change as a result of fire compared to the control units. Our results indicate that spring burns were the most successful at reducing woody stem density one year after burn. However, reduction in woody stem density may not be the only management objective. Our results also suggest that spring burns create a uniform understory of shrub regeneration, which may reduce heterogeneity on the landscape. Recent research suggests that high severity burns, which create a single cohort of regenerating woody shrubs, reduce habitat quality for the bird community (Zlonis et al., 2019). Thus, natural resource managers should view fire season as a tool for supporting a variety of outcomes in lowland brush ecosystems.


University of Minnesota M.S. thesis. July 2019. Major: Natural Resources Science and Management. Advisor: Rebecca Montgomery. 1 computer file (PDF); ix, 72 pages.

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Knosalla, Lori. (2019). Seasonal prescribed burning impacts to northern Minnesota lowland brush ecosystem plant communities. Retrieved from the University Digital Conservancy,

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