Population dynamics of the spruce bark beetle Ips typographus in forest conservation areas and the interaction with biodiversity and natural enemies

Abstract: Biodiversity is rapidly decreasing and in need of more conservation efforts. However, the tree-killing European spruce bark beetle, Ips typographus (L.), has made forest conservation controversial by affecting conservation areas and possibly adjoining managed forests, yet is still a keystone species leaving decaying wood promoting biodiversity. To improve our understanding of the influence of conservation areas, this study investigated the difference in population dynamics of the spruce bark beetle, abundance of natural enemies and species richness of arthropods, including their association to one another and differences in the environment, compared between managed forests, woodland key-habitats and nature reserves during an outbreak in southern Sweden. Bark samples were collected from standing trees in the different managements, and in each bark sample all arthropod species and information of the spruce bark beetle’s population dynamics were recorded. Additionally, environmental data of local and regional landscape was obtained though remote sensing. The results showed that the conservation areas included in this study had e.g., higher spruce volumes and drier ground compared to managed forests and consequently had an environment theoretically more prone to attacks. Despite this, in particular nature reserves, did not have higher attack density, offspring production or reproductive success of spruce bark beetles, compared to managed forests. Under similar population pressure, even lower rates than managed forests. Furthermore, nature reserves possessed higher species richness per m2 bark compared to managed forests, and generally higher abundance of natural enemies per m2 bark compared to the other two managements. This suggests that nature reserves are able to allow natural ecological processes and maintain vital ecosystem functioning among spruce bark beetles and their natural enemies, resulting in high biodiversity and a natural control with possibly relatively high spruce bark beetle mortality. However, the influence of woodland key-habitats is more unclear and remains to be addressed.