Department of Physics, Chemistry and Biology (IFM)

At a landscape level, old or dead trees are one habitat type that is decreasing in frequency. When trees grow old the internal woody tissues often get colonised by fungi. With time the tissue rots, birds can split up the tissue and insect larvae consume the softened wood. The hollows that are formed in the process become filled with residual woody debris and get mixed over the years with insect fragments, dead leaves, bird and mammal remains. This flour and saw-dust like material is called wood mould. Hollows take time to form and are more abundant in old and large trees. A wide range of invertebrates, mammals and birds are dependant on tree hollows as they provide larval feeding resources, resting or nesting places.

In southern Sweden, mixed deciduous forests are rapidly decreasing in favour of species poor coniferous forests. Clear-cutting forests, agricultural lands and overgrown pastures and meadows are habitat poor, fragmented landscapes which are negative for many species, especially for those using old hollow trees. Saproxylic invertebrate species use hollows with wood mould to a great extent and as a result of the reduced habitat availability in Europe many of the species have become threatened. These severe negative impacts on the saproxylic fauna, and the time-delay in natural development of their microhabitat, suggest that management action is justified.

One intervention to increase the amount and spatial distribution of microhabitat is to artificially create them. A successful way is to fill wooden boxes with substrates that imitates, or quickly develops into, wood mould. Although the short-term success of attracting saproxylic beetles to this kind of boxes has been documented, the knowledge of the succession of species over a longer time span remains unknown. The artificial wood mould in the boxes should decrease over time, due to larval consumption and fungal activity. Therefore the species richness and abundance would also decrease.

The overall aim with this study was to investigate the succession of saproxylic species in artificial habitats in the form of wooden boxes. A number of specific questions were addressed. 1) How has the species composition changed during a duration of six years? 2) How has the composition of the categories tree-hollow species, nest species or wood rot species changed? 3) Does the initial composition of artificial substrates affect the colonization of saproxylic beetle species or tree hollow species, nest species and wood rot species? 4) How does the distance from a dispersal source affect the saproxylic beetle species composition in the boxes?  5) How does the saproxylic beetle composition in the boxes compare to the composition in living hollow oaks in the region (see full article for results and discussion for this aim)?