Data from: Harvesting effects on wild bee communities in bioenergy grasslands depend on nesting guild

Conversion of annual crops to native perennial grasslands for bioenergy
production may help conserve wild bees by enhancing nest and food
resources. However, bee response to the disturbance of biomass harvesting
may depend on their nesting location, thus their vulnerability to nest
destruction, and the response of the forb community on which they forage.
Moreover, because bees have long foraging ranges, effects of local
harvesting may depend on the amount of natural habitat in the surrounding
landscape. We performed a large-scale one- and two-year experiment in
Michigan and Wisconsin, USA, respectively, to examine how grassland
harvesting, landscape context, and study year affect the forb community,
above- and belowground-nesting bee species richness, community
composition, trap nest emergence, and visitation rate. In Wisconsin,
harvesting increased forb richness, cover, and evenness compared to
unharvested control sites. Harvesting negatively affected
aboveground-nesting bee richness and emergence from trap nests, possibly
because of nest destruction during the previous harvest. By contrast,
harvesting positively affected belowground-nesting bee richness, possibly
because of the greater food resource availability and reduced thatch
allowing greater access to nesting sites in the soil. Harvesting also
affected bee community composition, reflecting the increase in
belowground-nesting species at harvested sites. Despite harvesting effects
on forb and bee communities, there was no effect on flower visitation
rate, indicating little effect on pollination function. We did not find a
harvest by landscape context interaction, which, in combination with the
negative harvesting effect on trap nest emergence, suggests that
harvesting can affect local population growth rather than simply affecting
forager aggregation in different resource environments. For bees, there
was no harvest by study year interaction, indicating a consistent response
over a short timescale. Similarly, in Michigan, belowground-nesting
species also responded positively to harvesting, which was more pronounced
in sandier soils that are preferred for nesting. However, other components
of the Michigan bee and forb communities were not significantly affected
by biomass harvesting. Overall, our study demonstrates that harvesting
grasslands can positively affect the 80% of bee species that nest
belowground by enhancing nest and/or forage resources, but that conserving
aboveground-nesters may require leaving some area unharvested.