Browsing by Subject "prescribed fire"

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    The Effect Of Season Of Prescribed Fire On Richness And Abundance Of Breeding Bird Species And Vegetation Structure In Minnesota Lowland Brush Ecosystems
    (2019-05) Hawkinson, Annie
    Lowland brush ecosystems provide critical habitat for diverse breeding bird communities in the western Great Lakes region of the United States. These ecosystems are disturbance-dependent and historically experienced fires occurring throughout plant growing and dormant seasons. Disturbance in brushland landscapes influences woody vegetation structure, which can increase in extent, density, and height without frequent or effective disturbance events. Woody vegetation structure has been shown to be important for breeding bird communities in upland and forest systems, but this has not been studied in lowland brush ecosystems. Additionally, there are few studies on how bird communities and lowland brush vegetation structure respond to fire. Currently, lowland brush ecosystems in the Upper Midwest are predominately burned during spring months when plants are dormant. This may not mimic historical fire effects because before fire-suppression and control, fires occurred throughout snow free seasons, including summer and fall. In forests and grasslands, plant and bird species have been shown to respond distinctly to different seasons of fire, with the response of bird species being related to changes in vegetation structure and its role in nesting and foraging. No studies on season of fire have been done in lowland brush ecosystems. We assessed baseline models relating bird species richness, bird total abundance, and abundance of frequently detected bird species to woody vegetation structure in lowland brush ecosystems. Frequently detected bird species included golden-winged warbler (Vermivora chrysoptera), sedge wren (Cistothorus platensis), and veery (Catharus fuscescens) which are Minnesota Species in Greatest Conservation Need. We then used a Before-After-Control-Impact experimental design to evaluate the magnitude in change in response to spring, summer, and fall fire treatments of the same bird and vegetation variables. This allowed us to determine vegetation characteristics that are important to breeding birds and how the responses of birds and plants relate to season of fire. Stem height and stem height diversity, which was a measure of vertical structural diversity, were related to the most frequently detected bird species and bird species richness. Although these vegetation variables did not respond significantly to spring, summer, and fall fire treatments compared to controls, they exhibited decreasing trends after fires. Additionally, changes in stem height were nearly statistically significant. Veery and yellow warbler (Setophaga petechia) decreased in abundance after summer (veery) and spring and fall (yellow warbler) season treatments and were related to stem height in baseline explanatory models. We posit that these species decreased in abundance due to decreases in stem height. In contrast, chestnut-sided warblers (Setophaga pensylvanica) increased in abundance after spring and fall fires. This species was also related to stem height and the number of woody plant species. Therefore, chestnut-sided warblers may have been responded to additional changes in vegetation from fire and notably, chestnut-sided and yellow warblers exhibited opposite responses to the same fire seasons even though these species exhibit similar life history traits. Bird total abundance increased after summer and fall fires, the 2 seasons when prescribed fires are not typically conducted in the Upper Midwest. In our explanatory baseline models, the null model best explained bird total abundance and so although we were unable to relate this response to vegetation measurements, we suggest this response be considered in future management. Based on our results and the mix of responses to spring, summer, and fall fire seasons, conducting prescribed fires during different seasons may support different breeding bird species. The overall breeding bird community may also benefit, especially if prescribed fire is implemented during the summer when plants are growing. Adding summer burns to disturbance management-regimes that are often restricted to the spring in lowland brush ecosystems may also provide managers with larger burn-windows.
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    Long-term effects of prescribed fire on vegetation structure, dynamics, and tree growth in red pine (Pinus resinosa Ait.) forests in north central Minnesota.
    (2016-05) Scherer, Sawyer
    Prescribed fire is increasingly being viewed as a valuable tool for mitigating the ecological consequences of long-term fire suppression within fire-adapted forest ecosystems. While the use of burning treatments in northern temperate conifer forests has at times received considerable attention, the long-term (>10 years) effects on forest structure and development have not been quantified. We describe the persistence of prescribed fire effects in a mature red pine (Pinus resinosa Ait.)-dominated forest in northern Minnesota, USA over a ~50 year period, as well as the relative roles of fire season and frequency in affecting individual tree and stand-level structural responses. Burning treatments were applied on 0.4 ha compartments arranged in a randomized block design with four blocks. Burning treatments crossed fire season (dormant, summer) and frequency (annual, biennial, and periodic), and include an unburned control for comparison. Treatments were applied from 1960 to 1970, with no further management interventions occurring since. Data were collected periodically from 1960 to 2014. Forest structural development trajectories were significantly altered by the application of fire treatments. Our results indicate that the effects of burning treatments on structural dynamics are not ephemeral, but rather alter stand development trajectories in the long-term. Further, burning altered shrub layer dynamics and community composition both in the short- and long-term. Both season and frequency of burning were important drivers of the response of the understory, with frequent summer season burns having the largest impact, including the greatest control of hazel brush.The persistent nature of these effects highlights their potential as a tool for long-lasting structural alterations in treated stands without compromising overstory tree growth and vigor. The lack of red pine recruitment throughout the duration of the study suggests that prescribed fire alone cannot regenerate this species, and that further alteration to overstory and seedbed conditions would be needed to secure new cohorts of this species.
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    Seasonal prescribed burning impacts to northern Minnesota lowland brush ecosystem plant communities
    (2019-07) Knosalla, Lori
    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.
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    Secretive Marshbird Response to Invasive Wetland Plant Management in the Prairie Pothole Region of Minnesota
    (2021-05) Hill, Nina
    Marshbirds are difficult to survey due their secretive nature and association with dense wetland vegetation. Recently developed standardized survey protocols are used to monitor patterns of abundance, primarily at large spatial scales, but also can be used to assess marshbird response to management. We estimated abundances of 5 species of marshbirds (American bittern [Botaurus lentiginosus], least bittern [Ixobrychus exilis], pied-billed grebe [Podilymbus podiceps], sora [Porzana carolina], and Virginia rail [Rallus limicola]) in relation to vegetation management techniques of Prairie Pothole wetlands. In northwestern Minnesota, management in autumn 2105 included herbicide application to wide-spread cattail (Typha spp.) mats with the goal to break up dense vegetation patches and restore wetlands to hemi-marsh conditions. In a before-after, control-impact study design we conducted standardized call-broadcast surveys for marshbirds during breeding seasons 2015 – 2018. We observed that American bittern, pied-billed grebe, sora, and Virginia rail abundances initially decreased, and then increased at 2nd and 3rd seasons post-treatment at sites where herbicides had been applied. In west-central Minnesota, long-term vegetation management included varying frequencies of multiple control methods. Using a habitat-informed detection probability we transformed bird counts to densities to compare abundances of marshbirds across survey locations surrounded by variable amounts of suitable habitat. We compared abundances of marshbirds among categories of wetlands with management histories of low frequency of prescribed fire, high frequency of prescribed fire, and high frequency of prescribed fire and grazing. Fire and grazing as applied in the system we studied did not appear to influence Prairie Pothole Region wetland characteristics enough to result in changes in marshbird abundance, but abundance of marshbirds was related to characteristics of individual wetlands that did not appear to respond to fire and grazing. Pied-billed grebe abundance was positively associated with higher areas of open water, soras were more abundant in wetlands with high ratios of open water to emergent vegetation, and Virginia rails were more abundant in wetlands with scrub-shrub wetland cover types.