In Southern Sweden, wood-living beetles that use oak trees are a species-rich and threatened animal group in modern forestry and agriculture. According to new research from the University of Gothenburg, it was revealed that management with conservation thinning could be an effective way to promote these beetles in the long term.
With the modernization of traditional forestry in the 20th century, many of the forests in the southern and middle parts of Sweden became denser and darker than they had been before. For many species in sunlit and open woodland with oak trees as their habitat, this process has meant an increased risk of extinction.
Oskar Gran from the Department of Biological and Environmental Science said that these insects represent a large part of the biodiversity that humans have committed to preserving by law and through international agreements. In addition to being beautiful and fascinating, they also play an essential role in stabilizing forest ecosystems.
Gran researched in the Sweden Oak Project at the University of Gothenburg, a long-term research project evaluating management alternatives for overgrown oak forests in southern Sweden.
There are 25 pairs of forest sites that the Oak Project was studying. In each pair one site is allowed to develop freely, and one is actively managed through conservation thinning. In the thinned area, about a quarter of the tree biomass is harvested for the benefit of oak trees and certain groups of organisms. Then, they followed up with the results of the two management alternatives.
Nature conservation lacks long-term, experimental evaluation of different management alternatives. That makes studies such as those within the Oak Project very important as a way of finding out of the study's conservation measures are correct.
Wood-inhabiting beetles are a species-rich animal group with about 400 types on the Swedish Red List of threatened and near threatened species. In the new study, Oskar Gran and his team evaluated how management has impacted wood-inhabiting beetles connected with oak trees.
Gran emphasized that they previously knew that they responded positively to the thinning immediately after the management intervention. But the new study revealed that the effect has continued and even been strengthened after ten years.
The number of wood-inhibiting beetle species connected with oaks has even increased by one third compared with the forest areas that have remained untouched. Gran maintained that this result surprised them because they expected that regrowth after thinning would have been detrimental to the animal group. Also, the researchers encountered several of species that were only in the conservation-thinned areas and not in the untouched ones.
