HOLOCENE FOREST ENVIRONMENTS IN SOUTHERN SWEDEN AND WOOD LIVING INSECTS

Many insect species that today are threatened and thus are included in national red lists in Europe are wood living animals. The main reason is that many of their habitats and food substrates are diminishing, this trend has been accelerating during the last century. The structure of forest ecosystems, such as openness, is also considered to be an important factor for survival. This is probably the case for a number of species with their northernmost geographical range, e.g. southern Scandinavia, where they are dependent on a certain amount of sun exposure. Within nature conservation there is fluently a discussion weather many of the presently rare wood living insects are relicts from undisturbed primeval forests or if the species have survived in semiopen forest environments during the Holocene. The latter opinion often propose grazing and browsing by megaherbivores as the major impact on woodlands, before the semiopen to open cultural landscape maintained by Man. Unfortunately, Holocene palaeoecological research have so far focused relatively little on changes in forest structures and the role of insects in particular. I here present the first results based on multidisciplinary studies, including analyses of pollen, macroscopic plant remains and subfossil insects. Peat columns have so far been obtained and sampled from twelve small bogs in southern Sweden. The results suggest a mosaic structure of different types of woodlands rather than closed primeval forests before the agricultural introduction around 6000 years ago. The major disturbance factor seems to have been fire, even where deciduous trees were dominating. There are no indications (e.g. plant indicators, dung beetles) for intense grazing or browsing during the first half of the Holocene, except from the earliest part. During late Holocene particularly grazing was an important disturbance in the woodlands, together with fires. A relatively high number of saproxylic beetles that today are regionally extinct or very rare were recorded from the main part of the Holocene, except from the last centuries when the biodiversity declined.