Forests are critically important to global pollinator diversity and enhance pollination in adjacent crops

Abstract

Although the importance of natural habitats to pollinator diversity is widely recognized, the value of forests to pollinating insects has been largely overlooked in many parts of the world. In this review, we (i) establish the importance of forests to global pollinator diversity, (ii) explore the relationship between forest cover and pollinator diversity in mixed‐use landscapes, and (iii) highlight the contributions of forest‐associated pollinators to pollination in adjacent crops. The literature shows unambiguously that native forests support a large number of forest‐dependent species and are thus critically important to global pollinator diversity. Many pollinator taxa require or benefit greatly from resources that are restricted to forests, such as floral resources provided by forest plants (including wind‐pollinated trees), dead wood for nesting, tree resins, and various non‐floral sugar sources (e.g. honeydew). Although landscape‐scale studies generally support the conclusion that forests enhance pollinator diversity, findings are often complicated by spatial scale, focal taxa, landscape context, temporal context, forest type, disturbance history, and external stressors. While some forest loss can be beneficial to pollinators by enhancing habitat complementarity, too much can result in the near‐elimination of forest‐associated species. There is strong evidence from studies of multiple crop types that forest cover can substantially increase yields in adjacent habitats, at least within the foraging ranges of the pollinators involved. The literature also suggests that forests may have enhanced importance to pollinators in the future given their role in mitigating the negative effects of pesticides and climate change. Many questions remain about the amount and configuration of forest cover required to promote the diversity of forest‐associated pollinators and their services within forests and in neighbouring habitats. However, it is clear from the current body of knowledge that any effort to preserve native woody habitats, including the protection of individual trees, will benefit pollinating insects and help maintain the critical services they provide.

Host and floral communities shape parasite prevalence and reproduction in intensively managed forests

“…While management practices that restore pollinator communities in some working landscapes (especially agriculture) are well‐established (e.g., Kremen et al, 2019), our understanding of how to manage intensively managed forests for pollinators lags behind (Rivers, Galbraith, et al, 2018). This is likely because, until recently, forests were not seen as providing suitable habitat for bees (Rivers & Betts, 2021; Ulyshen et al, 2023). Our study and others have shown that intensively managed forests can support diverse and abundant bee and flowering plant communities (Rivers & Betts, 2021; Zitomer et al, 2023), and that management to enhance floral diversity may be able to bolster the utility of these forests for bee conservation.…”

Social but not solitary bee abundance tracks pollen protein accumulation in forest canopy gaps

“…Temporal mismatch between floral nutritional availability and native bee foraging activity (Figure 1) can decouple ecological networks and result in species loss (Kudo & Ida, 2013; Ogilvie & Forrest, 2017), as bees must be able to access floral protein sources (pollen) for brood provisioning in order to maximise fitness. For example, there is increasing recognition of the importance of resources from canopy trees and spring ephemerals (Ulyshen et al, 2023), particularly for early emerging bees such as queen bumblebees (Mola, Hemberger, et al, 2021), but early season forest plants may be declining hence adding stress to critical bee life stages (Mola, Richardson, et al, 2021). These temporal shifts in both floral bloom and bee activity periods are highly species‐specific and poorly understood (Solga et al, 2014).…”

Factors driving bumble bee (Hymenoptera: Apidae: Bombus) and butterfly (Lepidoptera: Rhopalocera) use of sheared shrubland and young forest communities of the western Great Lakes

“…are larval host plants for hundreds of caterpillar species (Narango et al 2020). In summary, the greatest pollinator diversity is supported by a healthy forested-landscape with a balance of age classes to support varying species specific and life cycle needs (Ulyshen et al 2023).…”