Edgewood College Madison, Wisconsin, United States
Abstract: Restoration and management of oak woodlands in the Upper Midwest often involves the removal of invasive shrubs to open the understory and promote regeneration of native understory vegetation. Prescribed burning is frequently used in combination with shrub removal to limit regrowth of woody invaders and favor fire-adapted understory forbs and graminoids. While hand-clearing of woody shrubs has long been used for mechanical removal of woody invasive plants, the use of forestry mowers has become increasingly common, particularly on larger restoration sites. However, little is known about the differential effects of hand-clearing and forestry mowing on native and non-native understory vegetation, and even less is known about how these methods impact the efficacy of using prescribed fire to promote restoration of forest understory communities. Forestry mowing results in the accumulation of course woody debris, whereas hand clearing typically involves complete removal of the cut shrubs. The differences in litter quality and quantity therefore can differ greatly between the two clearing methods and differentially affect understory plant regeneration. This study aims to compare these two shrub-removal methods and consider how each, with and without prescribed burning, might impact regrowth of native and non-native understory vegetation. Five sites were selected at the UW-Madison Arboretum’s Lost City Forest in spring of 2021. At each site, five 20x20-m plots were established. Pre-treatment vegetation sampling was conducted in summer 2021. In fall of 2021, two plots at each site were hand cleared, two were cleared using a forestry mower, and one was left uncleared as a control plot. One hand-cleared and one mowed plot at each site were randomly selected to be burned in spring of 2022. Post-treatment vegetation sampling was conducted in summer 2022. Initial results suggest that while the percent cover of non-native invasive shrubs was significantly reduced by both clearing methods, the number of new non-native seedlings (especially common buckthorn, Rhamnus cathartica) significantly increased in both the hand-cleared and mowed plots compared to the control plots. There was little effect of burning on percent cover or seedling recruitment. Mowed plots showed a greater reduction in non-native vegetation than hand-cleared plots, but native vegetation increased much more in hand-cleared plots compared to mowed plots.
