Större svartbagge Upis ceramboides i norra Hälsingland : förekomst, substratkrav och effekter av skogsbrukets naturvårdsåtgärder

Sammanfattning: Many wood living insects are considered threatened by modern forestry due to the reduction in amount of dead wood. During the last decade various methods have been used to enhance the quantity of dead wood in managed forests. However little is known how and if these methods are aiding saproxylic insects. The threatened tenebrionid beetle, Upis ceramboides, is already extinct in southern Sweden. It develops in white rotted dead birch (Betula spp) and requires sun-exposed sites. The species is probably favoured by the effect of logging if the right methods are used. The aim of the study was to study the biology, habitat associations and distribution pattern of the species to be able to evaluate the conservation strategies. The study took place in a 200 km2 area in northern Hälsingland, north central Sweden. Three stand-types, unburned clear-cut (24 areas), burned clear-cut (four areas) and forest (three areas) were investigated. Three unburned clear-cuts and one burned clear-cut were each investigated carefully with transects of a 2500 m2 area. The forest areas were totally investigated (2500 m2 each). Variables reflecting habitat quality were measured and related to occurrence of U. ceramboides. The species was uncommon in the studied landscape and occurred only in seven unburned and one burned clear-cut. Totally 79 larvae were found, only on birches, while two adults were found on willow (Salix caprea). The species occurred mostly in sun-exposed, thin, moderately decayed wood with little contact to the ground. The larval substrate had been colonised by several different white rot fungi. Within clear-cuts the species often had an aggregated occurrence. There was a significant positive correlation between the proportion of inhabited birch-substrates and bark area (m2) per transect. Several larvae, of different sizes, could be observed in the same birch-substrate. There was a positive significant correlation between the larvae head-capsule size and the decay stage of the wood. Birchwood is suitable for larval development for about five years. To favour the species it is important to create suitable substrates in areas where U. ceramboides is present today and in close vicinity of existing populations. It is also important to keep the deadwood undamaged during all production steps. Other deciduous trees with thick bark that are probably used as hiding and overwintering places for U. ceramboides should also be saved.