Can a species confined to primeval-like forests reach fragments of habitat in a managed landscape?

Abstract

The Swedish government has taken initiatives to intensify the conservational work at landscape scale. That is, to analyse different needs for biodiversity, and together with different actors, for example the forestry sector, find ways for long time conservation of the biodiversity.

Old growth, moist spruce forests constitute an important habitat for a substantial part of the species belonging to the taiga. One of them is the saproxylic beetle Pytho kolwensis, in Sweden considered as endangered. The larvae feed on cambium on newly fallen spruces for about five years. After 10-15 years the log can no longer provide food for the larvae and the adult beetles have to lay eggs in other spruce logs. The logs are typically large trunks of old spruces (> 200 yr.), a structure no longer produced in the managed forest landscape. This type of old forest is today only found as fragments and the species is known from only about 20 localities in Sweden.

Although the habitat today is rare, it is comparably easily restored. Given enough time a spruce stand of average productivity will eventually become suitable for P. kolwensis, as long as no large-scale disturbance takes place. The question is; will the adult beetles find these fragments of suitable forest stands in a landscape dominated by young managed stands, i.e. is the dispersal ability of the species sufficient?

In order to reach an answer to the question, 54 spruce logs were felled in 2010 at different distances, at most about one kilometre, from a forest stand with a strong population of P. kolwensis. Preferably large old spruces were chosen, but in some cases, no such were found. Hence felled trees were 72-326 yr. old with a breast height diameter of 23-55 cm. Some of the cut trees were in stands in close vicinity to the source stand. Other were situated in stands surrounded by open areas without trees, habitat that possibly is avoided by flying adult beetles.

The study is performed in the central part of Sweden and is run by the County administration of Västernorrlands län. The inventory of felled trees will continue until all logs have passed the suitable stage as habitat for kolwensis-larvae. On ECCB 2018 the first results are presented, showing that so far some of the nearest situated logs have been colonized. The presentation also embraces what type of logs that have been used by the species.