Navigating nuance in native bee responses to grassland restoration management: A multi-ecoregional approach in the Great Plains

Abstract

Habitat fragmentation due to agricultural intensification leads to losses of biodiversity and ecosystem services such as pollination. Wild bee declines pose a serious threat to pollination stability and are expected to be most severe in agricultural landscapes, providing the impetus for grassland restoration efforts like the Conservation Reserve Program (CRP) to establish pollinator habitat via forb-enhanced plantings. One form of management not applied to CRP forb-enhanced plantings is grazing. Given historical adaptation of Great Plains ecosystems to large grazers such as bison, it is possible that grazing-induced benefits to pollinators and forb communities have been overlooked. Few studies have examined the effects of restoration management on grassland native bees. Specifically, there is need to a) assess the effects of restoration plantings on native bees throughout Great Plains ecoregions, and b) examine how associated management practices, such as grazing, affect bee communities. This study is the first of its kind to assess bee and forb responses to grazing and restoration plantings across multiple ecoregions of the Great Plains. We surveyed native bee and forb communities on 108 CRP fields throughout the sand, short-, mixed-, and tall-grass prairie ecoregions of Kansas. CRP fields were either a) forbenhanced or primarily grass-planted and b) not grazed or grazed at low-intensity. Overall, we found that floral cover was the most important predictor of bee responses. Forb-enhanced restorations did not differ in floral cover or richness, but still had positive effects on native bees. Bee community responses to grazing were mostly positive with one exception: bee diversity decreased on mixed-grass, grazed fields. Additionally, bee communities responded to grazing only after grazing had ceased. Our findings provide novel insight into bee community responses to land management on restored grasslands in a predominantly agricultural Great Plains landscape.