Honeybees play a crucial role in pollination, contributing significantly to the world’s food supply. Unmanaged forests are considered the native habitat of the Western honeybee, Apis mellifera, and are assumed to provide essential pollen and nectar sources. However, managed forests may not offer the same abundance of resources. A recent study by Rutschmann and colleagues in the Journal of Applied Ecology reveals how managed forests could be improved to better support honeybee foraging.
The researchers capitalised on a unique communication behaviour known as the waggle dance to investigate honeybee foraging in a deciduous forest region in southern Germany. Forager bees perform this dance to communicate the location, distance, and direction of food sources to their fellow bees.
The study analysed 2022 waggle dances from 12 honeybee colonies placed in the centre of landscapes with varying degrees of forest cover (50%–99% at a 2 km radius) from March to August 2019. This allowed them to identify foraging distances and habitat preferences throughout almost an entire foraging season. By linking dance information with colony weight recordings, the researchers could assess the role of landscape composition and the contribution of different habitat types to colony weight gain.
The study found that foraging distances generally increased with the amount of forest in the surrounding landscape, suggesting that food resources in the forest are less abundant. This effect was strongly dependent on the season and was more pronounced for pollen than for nectar foraging. Although colonies in forest-dominated landscapes had to fly further, forest cover did not significantly affect colony weight.
Compared to expectations based on the proportions of different habitats, colonies foraged more frequently in grassland and cropland than in deciduous and coniferous forests. Late summer was a particularly challenging period for pollen foraging in forests.
“Especially in late summer, the supply of pollen in the forest was not guaranteed or insufficient, besides this being an especially critical time for the bee colonies and their brood,” says Rutschmann in a press release. One of the main reasons for this, he says, is the tree species beech, which makes up more than 40 per cent of the tree population in the Steigerwald: “Beech forests are dark, there is not much growing on the ground. Hardly any plants can cope with the light conditions in beech forests after the canopy closes, so a diverse herb layer that would be so important for bees is missing,”
However, during a phase of colony weight gain in early summer, forests were used for nectar and honeydew foraging at levels close to expectation, emphasising the importance of forests as a complementary carbohydrate source during specific periods of the year. Rutschmann and colleagues write in their article that forest managers could help pollinators with some simple changes.
Therefore, if it is the goal to promote native wild populations of honeybees, other social bees and resources for managed honeybee colonies within managed forests, we recommend supplementation of forest stands by native insect-pollinated trees (e.g. willows, linden, maple, cherry, alder buckthorn, mountain ash and sweet or horse chestnut) and identifying and promoting forest-dwelling plant species of the herb and shrub layer, especially those that produce pollen in late summer. Moreover, pollinator-friendly management should focus on transitional structures with open areas (e.g. clearings and roadside corridors) in closed forest landscapes. At larger scales, we propose the creation of landscapes with a high diversity of different forest types and open habitats to foster pollinating insects.Rutschmann et al. 2023
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Rutschmann, B., Kohl, P.L. and Steffan-Dewenter, I. (2023) “Foraging distances, habitat preferences and seasonal colony performance of honeybees in Central European forest landscapes,” The Journal of Applied Ecology. Available at: https://doi.org/10.1111/1365-2664.14389