2017-2019 SW ND Patch-burn Grazing Pollinator Study - Butterfly data

Our study compared how sheep versus cattle herbivory affected floral resources and butterfly abundance across low-diversity, former Conservation Reserve Program (CRP) pastures managed with patch-burn grazing—a management practice that seeks to create heterogeneity by allowing grazers and fire to interact spatially and temporally. We conducted research in six, 65-ha pastures, with three pastures grazed by sheep and three grazed by cattle. Animals grazed pastures from May until September. Each pasture was divided into quarters, delineated by a 20’ fire break disked to mineral soil, however, only the exterior of the pasture was fenced allowing for livestock movement across the entire management unit. We sampled butterflies from late-May to mid-August of 2017-2019 with three sampling periods per season to quantify butterfly community composition and individual species’ densities. There were 12, 100 m butterfly transects per pasture, three in each burn unit, for a total of 72 butterfly transects. We conducted LTDS surveys by walking 100 m transects at an approximate rate of 10 m · min-1 and recorded all butterfly species on either side of the transect, as well as the perpendicular distance from the transect. After each butterfly survey (i.e., three times per season), we counted all flowering ramets within 1 m of either side of the transect to quantify how different grazers affected floral resources. Additionally, once per season, we recorded vegetation structural characteristics and vegetation composition along each transect. We collected vegetation data every 10 m on both sides of the 100 m transect for 20 sampling points per transect. We measured vegetation structure (visual obstruction) with a Robel pole marked in 0.25 dm increments (Robel et al. 1970) with four visual obstruction readings at each point. The observer also recorded the tallest standing live and standing dead vegetation at each sampling point. Finally, we assessed vegetation composition by species, and percent cover of standing litter, ground litter, and bare ground at each sampling point using a 0.5 m2 frame and the Daubenmire (1959) cover classification (0-5%, 5-25%, 25-50%, 50-75%, 75-95%, 95-100%) and measured litter depth inside each corner of the 0.5 m2 frame.