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.