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Bees need more trees

A bee at its nest. Photo.
A red mason bee at its nest. The new study shows that trees could be just as important as flowers for bees' survival. Photo: Melanie Karlsson

There is an increasing awareness that pollinating insects need flowers rich in pollen and nectar. A new study shows that trees can be just as important for survival – at least for the red mason bee, and probably for other wild bees too.

Researchers have investigated the types of habitats and flowers in the agricultural landscape that benefit the reproduction of the red mason bee – a common solitary bee found in southern Sweden, which is active early in the year. A noticeable finding is that a general availability of trees in the landscape increases the reproduction of bees.

Oak is a favourite

“We noticed that an increased quantity of trees benefited the bees. In part, this can be explained by the fact that the bees mainly collected pollen from oak, especially early in the season, but also because wooded areas could provide nesting habitats for bees”, says Johanna Yourstone, doctoral student at the Department of Biology at Lund University in Sweden and principal author of the study, which was published in Biological Conservation.

In the study, the researchers were also able to show that the bees preferred oak pollen compared to their second largest source of pollen in early spring – maple. The greater the availability of oak, the more oak pollen collected by the bees. Maple, on the other hand, was mainly collected when there was low availability of oak in the area.

Pollen from buttercups

In addition to trees, the researchers observed that the presence of buttercups and oilseed rape benefitted the bees. The bees collected a great deal of pollen from buttercups during the latter part of their lives, which most likely explains the positive effect of buttercups on reproduction. By contrast, the bees did not collect much pollen from oilseed rape, leading the researchers to believe that oilseed rape was primarily important as a source of nectar.

According to Johanna Yourstone, this study confirms past experiences regarding the importance of different types of resources being available to bees and that the resources need to be available over time as well. 

The article "Effects of crop and non-crop resources and competition: High importance of trees and oilseed rape for solitary bee reproduction" has been published online in Biological Conservation.