Habitat restoration benefits wild bees: A meta‐analysis

Abstract

Pollinator conservation is of increasing interest in the light of managed honeybee (Apis mellifera) declines, and declines in some species of wild bees. Much work has gone into understanding the effects of habitat enhancements in agricultural systems on wild bee abundance, richness and pollination services. However, the effects of ecological restoration targeting “natural” ecological endpoints (e.g. restoring former agricultural fields to historic vegetation types or improving degraded natural lands) on wild bees have received relatively little attention, despite their potential importance for countering habitat loss. We conducted a meta‐analysis to evaluate the effects of ecological restoration on wild bee abundance and richness, focusing on unmanaged bee communities in lands restored and managed to increase habitat availability and quality. Specifically, we assessed bee abundance and/or richness across studies comparing restored vs. unrestored treatments and studies investigating effects of specific habitat restoration techniques, such as burning, grazing, invasive plant removal and seeding. We analysed 28 studies that met our selection criteria: these represented 11 habitat types and 7 restoration techniques. Nearly all restorations associated with these studies were performed without explicit consideration of habitat needs for bees or other pollinators. The majority of restorations targeted plant community goals, which could potentially have ancillary benefits for bees. Restoration had overall positive effects on wild bee abundance and richness across multiple habitat types. Specific restoration actions, tested independently, also tended to have positive effects on wild bee richness and abundance. Synthesis and applications. We found strong evidence that ecological restoration advances wild bee conservation. This is important given that habitat loss is recognized as a leading factor in pollinator decline. Pollinator responses to land management are rarely evaluated in non‐agricultural settings and so support for wild bees may be an underappreciated benefit of botanically focused management. Future restoration projects that explicitly consider the needs of wild bees could be more effective at providing nesting, foraging and other habitat resources. We encourage land managers to design and evaluate restoration projects with the habitat needs of wild bee species in mind.

Native plant abundance, diversity, and richness increases in prairie restoration with field inoculation density of native mycorrhizal amendments

“…Positive feedback between native plants and native AM fungi can amplify these benefits over time (Koziol & Bever ). Amending native AM fungi in restorations can improve native establishment, and greater native establishment can in turn improve habitat quality for wildlife (Debinski & Babbit ; Tonietto & Larkin ).…”

Habitat enhancements rescue bee body size from the negative effects of landscape simplification

“…Recent studies have confirmed that habitat enhancements are most effective in simple, agriculturally dominated landscapes where they result in a high contrast between the local availability of floral resources and those available in the broader landscape (Scheper et al, 2015). Increases in pollinator abundance in response to on-farm habitat enhancements have been documented in the US and Europe (Scheper et al, 2015;Tonietto & Larkin, 2018;Williams et al, 2015), yet the mechanisms driving these improvements at the population level have not been determined. Behavioural responses may drive the observed increase in abundance through increased attraction of bees from surrounding habitats or alternatively, population responses may occur due to increased fitness of bees subsidized by the floral resources provided by habitat enhancements (Senapathi et al, 2015).…”

Assessing the risk of bias in choice of search sources for environmental meta‐analyses

“…Thirty articles from 22 journals out of 28 139 unique records retrieved by the searches for meta‐analyses met all the eligibility criteria (flow diagram: Appendix S3; list of eligible articles: Appendix S4; list of articles excluded at full text and unobtainable records: Appendix S5), resulting in 137 eligible meta‐analyses (ie, 137 overall mean effect sizes without duplication of primary studies between meta‐analyses presented in the 30 articles, 32‐61 hence retaining independence of individual effect sizes). These 30 eligible meta‐analytical articles conducted diverse searches in addition to the single‐platform search in WoS (Figure 3).…”