Are bumblebees limited by floral resource availability due to cattle grazing in boral forest pastures? : The effects of seasonality and cattle grazing on bumblebees in boral forest pastures
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Boreal forests provides a wide range of ecosystem services and goods that serve the Norwegian community. For centuries humans have utilized this resource in commercial sectors through timber production and traditional forest pastures for livestock. However, these long traditions of keeping livestock in forest pastures has been subject to change as a result of re-establishing carnivore populations and agricultural intensification. The relationship between flowering plants and their pollinators plays a central role in securing a harmonious and healthy ecosystem in forest pastures. To ensure a viable population of wild pollinators in Norway, the Norwegian government aims to further increase knowledge on how to safeguard and provide suitable pollinator habitats. In line with the request for a more carnivore compatible method for keeping livestock, the focus is directed to re-establish beef cattle (Bos taurus) in these forest pastures. These initiatives combined calls for effort to look at the effects of grazing on biodiversity, as there is a lack of previous research on the matter in boreal forest pastures. This study investigates the effect of cattle grazing on bumblebees and their floral resources in the boreal forest, by comparing observations from areas with and without cattle grazing during the peak flowering season. The main objective is to study the effect of season on variation in floral resources, how cattle presence affects resource availability and how this in turn might affect the bumblebee diversity. The study shows that although there is less total abundance of floral resources in areas with cattle, there is no significantly negative relationship between cattle presence and the abundance and richness of bumblebees. The timing of flowering varied between different plant species, some reaching their peak earlier in the season and some later. These findings suggest that the bumblebees were not limited by less available resources because of cattle grazing. The consequences of cattle grazing in forest pastures may there for not pose a negative effect on bumblebees with a low intensity grazing pressure. However, further in-debt research about other plant-pollinator interactions in the area is needed to be able to give a more accurate inference of the effects of grazing.