Feed the bees and shade the streams: riparian shrubs planted for restoration provide forage for native bees

Abstract

With evidence of pollinator declines and an increasing focus on restoration, interest is growing in investigating floral resources for native bees. Although native bees forage on shrubs, few studies have explored the pollinator communities of native shrubs and none have examined shrub-pollinator interactions in riparian areas of the northwestern United States. Life history traits of shrubs may make them particularly important resources for bees, especially in early spring-a key point in the lifecycle of many bee species. We conducted extensive hand-net surveys over 2 years in a large riparian restoration project in the Pacific Northwest to understand bee-flowering plant interactions with the aim of guiding future restoration efforts. Although forb blooming stem abundance and richness were higher than that of shrubs in spring, 57% of bees observed foraging were on willow (Salix spp.), a commonly planted riparian shrub. Season-long, bee community composition on shrubs differed from that of forbs. Bee species diversity was highest on wax currant (Ribes cereum) and willow in early spring (April) and on black hawthorn (Crataegus douglasii) and mallow ninebark (Physocarpus malvaceus) later (i.e., June -July). Some bees showed a strong preference for wax currant and black hawthorn, both of which are more resistant to ungulate herbivory than other shrubs. Our results suggest that riparian restoration practitioners could consider using shrubs that provide forage to a diverse community of pollinators and improve stream health by shading and stabilizing banks. Planting bee-friendly shrubs can help accomplish multiple restoration goals and leverage limited restoration funding.

Attraction of Bees to Native and Introduced Willows (Salix spp.)

“…It has been previously suggested that planting willows near fruit and berry crops is an effective way to increase fruit production via increased pollination [14,51]. Both native and introduced willows may be strategically planted near agricultural fields along with pollinator-dependent crops to provide essential nutrient resources for bees prior to the mass flowering of agricultural crops.…”

“…For example, willows support a high density of breeding bird communities by providing services such as nesting, food, and stopover sites [13]. Willows are considered an ecosystem "foundation species", due to the high number of insects they bolster [14]. Furthermore, willow short rotation coppice (SRC) plantations reduce the negative consequences of habitat fragmentation with the provision of food and shelter for a high proportion of animals that move from adjacent habitats into the plantations [15].…”

Phenologically Targeted Grazing: A Potential Sustainable Strategy for Native Bees in Semiarid Rangelands

“…Data from all five transects were combined, creating a single dataset for each site. As in other pollinator studies (e.g., Roof et al, 2018 ;Graham et al 2021 ;Mitchell et al 2021 ), we defined blooming stems as individual flowers or clusters of flowers arranged on a stem.…”

Restoring Riparian Ecosystems During the UN-Decade on Ecosystem Restoration: A Global Perspective

“…(Rood et al 2003;Golet et al 2011). The faunal diversity can indicate the success of riparian ecosystem restoration (Golet et al 2008 and2011;Gollan et al 2011;Wortley et al 2013;Mitchell et al 2021); however, a few studies have shown that not all species can be taken into account. For example, using prey availability was not successful in the evaluation of the restoration programme at lower Colorado River (Rubin et al 2019).…”