A survey of the saproxylic beetles (Coleoptera) in Dividalen, Troms county, northern Norway

The saproxylic beetle fauna in Dividalen (68.5-69 degree N), a tributary valley to Malselvdalen in the county Troms, has been investigated in the period 1993-1999 with nine different collecting methods. Dividalen is in the northern boreal forest region and has a mixture of pine (Pinus sylvestris L.) and different species of hardwoods, among which birch (Betula pubescens Ehr.) dominates. The collected material comprises more than 22.800 individuals (larvae, pupae and imagines) of 189 obligatorily saproxylic species. This constitutes more than 75% of all the saproxylic species found in the county. Twenty-four of the obligatorily saproxylic species found in Dividalen are redlisted in Norway. Fourteen species are reported for the first time from Troms county. A survey of the saproxylic beetles occurring in the inner parts of Troms gives the following grouping: a) northern species, i.e. absent in South Norway, b) ubiquitous species, i.e. species distributed throughout Norway and c) species with a gap in their distributions between South/Central Norway and Troms. Since a number of plant and animal species have a real break in their distribution between South/Central Norway and Troms (Finnmark), it is possible that several saproxylic species show the same pattern. We argue that the topography between Nordland county and Sweden gives a combination of factors which might contribute to these possible breaks.