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Conclusions

Landscape variables
In Östergötland County, the presence of T. depsarium was positively correlated with the amount of protected areas within 500 meters despite that not all of the areas contained the beetles preferred habitat. If this is true, this means that several small or a part of a larger protected area is beneficial for this species. Another landscape variable showing a strong correlation with beetle occurrence was amount of clear-cuts within 1000 meters from the pheromone trap.

This might seem contradictory to the negative influence from forestry in general, but often there are forgotten pine logs or smaller parts of logs with low economic value left in the open sun. Before the logs become too shadowed by regenerating forest, these logs provide useful, but temporary, breeding substrates for the opportunistic T. depsarium.

Distribution
T. depsarium was not evenly distributed in the landscape, but rather concentrated to a few areas, indicating isolated populations. Many of these isolated populations were thought to be small and therefore prone to extinction.

A majority of the sites in Östergötland had no beetles, despite no difference in pine log availability between empty sites and occupied sites. This further supports the idea of isolated populations of T. depsarium in the landscape. A continuous threat to this species is not only a decreasing mean age of the trees in Swedish forests due to forestry, but also an increasing densification of the forests when forest fires are excluded. This densification includes also nature reserves and other protected areas, which are meant to be refuges for threatened species.

Conservation implications
The problem with denser and darker forests has been recognised, and prescribed fires are carried out to promote fire dependent species. Although fire is the most natural way to open up the forests and making them warmer for demanding species, selective cutting and an active forestry are also important for more open forests. A prerequisite for a good effect from an active forestry is that at least some larger parts of pine logs are saved on the clear-cuts for conservation together with some seed trees of pine that are left even if they are felled by wind.


Responsible for this page: Agneta Johansson
Last updated: 05/11/15