Plant-pollinator networks are enhanced in habitats managed for sagebrush restoration in western Colorado

Encroachment of pinyon pine and juniper spp. into sagebrush communities is widespread in the western United States and reduces shrub and herbaceous vegetation. Accordingly, managers often employ mechanical treatments targeting conifer tree removal as a restoration effort to promote sagebrush establishment. However, there is presently no information on how these restoration practices impact plant-pollinator networks. To evaluate effects of sagebrush restoration on pollination networks, we conducted a study across 30 sites in two National Conservation Area, Dominguez-Escalante and McInnis Canyons; we selected sites which were either conifer-encroached or post-restoration (treated with mastication). In each site, we netted bees and recorded plants they, and collections were done three times during the growing season (May, June and July). We used network analysis statistics to generate estimates of interaction frequency between bees and flowers in restored and non-restored habitats. Network analysis revealed evidence for positive effect of sagebrush restoration treatments on pollination networks and we observed higher connectivity in restored habitats. A diverse community of Osmia spp. and Lasioglossum spp. were found visiting flowers in both habitat types, but Megachile and Andrena spp. were more abundant and more likely to interact with flowers in restored habitats. By late in the growing season (July) few native flowers were present, and most bees were netted while interacting with noxious weed species in roadside habitats. We conclude that sagebrush restoration treatments are likely to expand plant-pollinator networks, but invasive species may provide important late-season habitat for native bee pollinators in conservation areas.