Early spring orchard pollinators spill over from resource‐rich adjacent forest patches

Abstract

Pollinator communities are more abundant and diverse in agricultural matrices with more natural habitat, although the reasons for these correlations remain unclear. It is possible that forest fragments and edges provide resources for pollinators in important early weeks of spring, after which time those insects can then ‘spill over’ into crops such as apple orchards during bloom. To explore how forest edges may feed and therefore promote flower visitor communities in adjacent agricultural habitats, we sampled springtime pollinators in nine orchards and their adjacent forest edge canopies and understories. We identified pollen consumed by pan‐trapped bees and flower flies to assess if pollinators ate pollen where they were caught, and if their diets similarly ‘spill over’ from forest to orchard. We further explored sex differences in habitat usage. Our spatially replicated sampling found that bee and flower fly abundance peaks first in the forest understorey, then in the forest canopy and finally in the orchard. Analysis of digestive tracts showed significant usage of forest canopy pollen throughout the spring, especially before apple bloom. Pollinators had often eaten pollen from a different habitat than the one in which they were caught, suggesting frequent movement between habitats. Digestive tract pollen is an underused but powerful avenue for ecological insight. In Andrena, which are important orchard pollinators and one of the most abundant wild bee taxa in this study, male bees were primarily found in the woods but not the orchards where conspecific females were later active. Synthesis and applications: Forested areas, especially forest canopy trees, provide large amounts of early spring resources that facilitate build‐up and spillover of wild pollinator populations into apple orchards during bloom. Forests also provide critical habitat for male bees, which were rarely found in orchards. Despite their importance for bee reproduction, the needs of male bees are usually not considered in conservation planning. Overall, our data indicate that ensuring there is adequate forest habitat adjacent to orchards can improve the long‐term sustainability of pollinator populations that provide essential crop pollination services.

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

“…Because these resources are unevenly distributed within the three‐dimensional space between the forest floor and the top of the canopy, pollinators also exhibit uneven distributions across this vertical gradient (Ramalho, 2004; Bawa et al ., 1985; Appanah, 1981; Bawa, 1990). However, given the logistical challenges of accessing the canopy, our understanding of pollinator diversity and ecology near the ground far exceeds what is known from the upper reaches of forests (Ulyshen, Soon & Hanula, 2010; Dorey, 2021; Urban‐Mead et al ., 2023). With this limitation in mind, we briefly summarize current knowledge about the importance of both floral and non‐floral (e.g.…”

“…For example, in eastern North American forests, 20–60% of tree species, depending on the forest type, rely on animals for pollination (Regal, 1982). In temperate systems, many genera of insect‐pollinated trees are recognized as important early‐spring resources (Bertrand et al ., 2019; Allen & Davies, 2022; Urban‐Mead et al ., 2023) and seed set in some tree species (e.g. Prunus serotina Ehrh.…”

“…The proportion of animal‐pollinated tree species does not fully capture the importance of trees to pollinators, however. Wind‐pollinated trees are also increasingly recognized as pollen sources for bees (Kraemer & Favi, 2005; Splitt et al ., 2021; Saunders, 2018; Urban‐Mead et al ., 2023; Fig. 2A), although the conditions under which such pollen is preferred or nutritionally beneficial remain largely unknown (Wood et al ., 2021; Roulston, Cane & Buchmann, 2000).…”

“…Diverse landscapes are thought to promote habitat complementarity, ensuring floral and nesting resource availability across the landscape and throughout the year (Mallinger et al ., 2016; Mandelik et al ., 2012; Nery et al ., 2018; Moquet et al ., 2018; Mola et al ., 2021; Maurer et al ., 2022). Because peak flowering often occurs at different times in forests in comparison to crops and other land uses, for instance, forests can help sustain pollinator populations during periods of flower scarcity elsewhere (Urban‐Mead et al ., 2023). Moreover, many forests provide floral resources, as well as non‐floral sugar sources such as honeydew (see Section IV), throughout the year, thus providing greater continuity in resource availability than is typical of many crops and other anthropogenic habitats (Lentini et al ., 2012; Ferreira et al ., 2022).…”

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

“…In particular, small solitary bees may be especially impacted by nutritional availability due to shorter foraging ranges, relatively short lifespans and lack of colony support (Roulston & Cane, 2002). Various early season species, such as some Bombus , Osmia and Andrena spp., do not rely as heavily on forb pollen and may more commonly utilise pollen from shrub or tree species (MacIvor et al, 2014; Persson et al, 2018; Urban‐Mean et al, 2023; Wood et al, 2022). In the present study, Osmia spp.…”