Arid grassland bee communities: Associated environmental variables and responses to restoration

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In recent years restoration project efforts in arid grasslands of the Pacic Northwest have increased; however, little isknown about the bee communities in these areas or how restoration affects them. Native bees provide an essential ecosystemservice through pollination of crops and native plants and understanding their response to restoration is a high priority. Toaddress this issue, we conducted a three-year study in an arid bunchgrass prairie with three objectives: (1) describe the beecommunity of this unique grassland type and its temporal variability; (2) investigate environmental variables inuencing thecommunity; and (3) examine effects of restoration on the community. We identified 62 bee species and found strong seasonaland inter-annual variation in bee abundance, richness, diversity, and species composition. Unexpectedly, these temporaltrends did not correspond with patterns in floral resources; however, several variables were associated with variation inbee abundance, richness, and diversity among sites. Sites with high levels of litter cover had more bees, while sites withtaller vegetation or more blooming flowers had greater species richness but lower diversity. We found no detectable effectof restoration on bee abundance, richness, diversity, or composition. Species composition at native sites differed from those inactively and passively restored sites, which did not differ from each other. Restored sites also had fewer flowers and differingfloral composition relative to native sites. These results suggest that if grassland restoration is to benefit bees, efforts shouldfocus on both expanding floral resources and enhancing variables that influence nesting habitat.