Abstract
Hedgerows, flowering strips, and natural areas that are adjacent to agricultural land have been shown to benefit crop production, via the provision of insect pollinators that pollinate crops. However, we do not yet know the extent to which bee habitat in the form of urban gardens might contribute to pollination services in surrounding crops. We explored whether gardens might provision pollinators to adjacent agricultural areas by sampling bees from gardens in the Portland, Oregon metropolitan area, and estimating typical foraging distances in the context of commercial- and residential-scale pollination-dependent crops up to 1000 m from garden study sites. We estimate that garden bees could forage outside of the garden in which they were collected, and that when pollination-dependent crops (commercial-scale or residential-scale) are nearby, 30–50% of the garden bee community could potentially provide pollination services to adjacent crops, if urban bees readily cross boundaries and forage among habitat types. Urban gardens might thus be well-positioned to provision neighboring farms and food gardens with pollination services, or could serve as a refuge for pollinators when forage is scarce or crop management practices are inhospitable. The actual capacity of gardens to serve as a refuge for pollinators from agricultural fields depends upon the extent to which bees forage across habitat types. However, relatively little is known about the degree to which bees move among habitat patches in heterogeneous landscapes. We thus propose a research agenda that can document the extent to which gardens contribute to pollinator health and pollination services at the interface of urban, peri-urban, and rural landscapes. In particular, more data is needed on how landscape context impedes or promotes garden bee movement between habitat types.
Highlights
Multiple, interacting stressors have been identified as drivers of global bee decline [1,2,3,4,5,6,7,8,9]
We considered the extent of pollination-dependent agricultural land surrounding garden study sites, by comparing the percent of each garden bee community estimated to typically forage up to 250 m, 500 m, and 1000 m from a central foraging point, to the land area planted to pollination-dependent agriculture in buffers with radii of 250 m, 500 m, and 1000 m
Post hoc study, we explored the possibility of pollination service flow between urban, residential gardens, and adjacent agriculture
Summary
Multiple, interacting stressors (e.g., habitat loss and fragmentation, pesticide exposure and the spread of pathogens) have been identified as drivers of global bee decline [1,2,3,4,5,6,7,8,9]. In particular, appear at the nexus of many of these stressors, leading to homogenization of wild bee communities and an increased reliance on managed species for pollination services [10], even though managed bees appear less suitable for achieving high fruit sets in many systems [11]. Recent research has demonstrated that wild pollination services can be enhanced through the retention or restoration of small fragments of natural habitat situated within broader agricultural landscapes [6,7,12,13,14]. Ponisio and colleagues [14] hypothesize that, while agricultural landscapes act as an “ecological filter” through which only a restricted group of generalist pollinator taxa can pass, diverse and mature bee habitat fragments act as refugia that result in greater spatial heterogeneity in bee communities, and more robust pollination service to agriculture [12]. The growing importance of the peri-urban zone to pollinator-dependent crop yield is acute in the Pacific Northwest, where, since the mid-1990s, some cities have experienced a 45% expansion of the area planted for highbush blueberry, a highly-pollinator dependent crop [19]
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