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

Abstract

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.

Bioenergy crops, biodiversity and ecosystem services in temperate agricultural landscapes—A review of synergies and trade‐offs

“…In addition, many studies used a coarse biodiversity measure, such as unspecified biodiversity, which risks failing to understand the underlying ecological mechanisms that drive biodiversity responses to land-use change (Duncan et al, 2015;Tscharntke et al, 2012). Finally, and importantly, we found only four studies evaluating both biodiversity and ecosystem services, three European studies based on indirect measurements (Gutzler et al, 2015;Schulze et al, 2016;van der Hilst et al, 2012) and one North American empirical study (Spiesman et al, 2019). As an example, Gutzler et al (2015) investigated a bioenergy scenario for Brandenburg, Germany, with 1G maize cultivation arable land, and its effect on landscape scenery, water quality, energy provisioning, climate regulation, soil erosion and farmland birds.…”

Diversity of Flower Visiting Insects in Dry Grasslands and Vineyards Close to the City of Vienna with Special Focus on Wild Bees.

“…Further differences between grasslands and flower strips for bee species were manifested regarding the structure of microhabitats. This include the effects of nesting behavior (availability of cavity including snail shells) or in general the flower-richness of the surrounding and landscape heterogeneity (Rundlöf et al, 2008;Spiesman, 2017). Cultivation of vine rows and associated flower strips destroy small cavities, necessary as nesting habitats for bees.…”

Deep learning for identifying bee species from images of wings and pinned specimens

“…One of the most challenging aspects of bee ecology and conservation is classifying or identifying individuals by species. With more than 20,000 species globally, researchers may find tens to several hundred bee species to identify in any given study [e.g., [1][2][3]. The identification process requires a high level of taxonomic expertise because many species share similar and sometimes highly variable features.…”