Insect conservation in boreal forests

Abstract

Loss of tropical forests is the greatest threat to insect diversity globally, as tropical forests harbour the majority of all insect species and the destruction of tropical forests continues at the high annual rate of 0.5–1% (FAO 2001; Pimm 2001; Hanski 2005). The current estimate of globally extinct or threatened species of insects, a mere 0.07% of all insect species (IUCN 2004), does not imply a great threat to insects, but almost certainly this figure reflects more lack of knowledge rather than lack of real threat. A recent analysis of the past and current occurrences of Helictopleurini (Scarabaeidae) dung beetles in Madagascar suggested that forest loss has caused the apparent extinction of nearly half of the described species (Hanski et al. 2007). This result is strikingly consistent with the prediction stemming from the species-area relationship, as only about 10% of the original forest cover remains in Madagascar. Habitat loss is equally high or even higher in many other biomes. Mediterranean forests, woodlands and scrub, temperate steppe and woodland, and temperate broadleaf and mixed forests had lost more than 50% of their potential area before 1950 (MA 2005). The additional projected loss from 1990 to 2050 is greater than 10% of the potential area for tropical and sub-tropical moist broadleaf forests, for tropical and sub-tropical dry broadleaf forests, tropical and sub-tropical grasslands, savannas and shrublands, tropical and sub-tropical coniferous forests, as well as for montane grasslands and shrublands (MA 2005). At the regional scale, the area lost already exceeds 80% for 10s of the world’s 810 ecoregions, and is close to 100% for some of them (Hoekstra et al. 2005). In striking contrast, both the past and projected conversion of boreal forests is minimal, a few percent of their potential area (MA 2005). This may appear to cause little concern about biodiversity of insects and other taxa in boreal forests, but unfortunately such a conclusion is unwarranted. In the global assessments of habitat loss (MA 2005), no distinction is made between natural and managed forests. Extraction of timber and other forest products is compatible with maintenance of biodiversity if the intensity of resource use is not very high and if forest cover is mostly maintained. For instance, slash-and-burn agriculture as practiced in boreal forests in northern Europe in the 17 and 18th century affected large areas, but not the entire forested landscape, because of relatively low human population density and because much of the land is unsuitable even for this form of cultivation, and hence the overall and large-scale impact on insect diversity was probably minor. In northern Europe, and increasingly in other boreal parts of the world, the situation has changed dramatically in the past decades with forestry becoming highly industrialised. I take as an example Finland, which I know best and where industrial forestry is probably more advanced than anywhere else in the boreal forest region in the world. Nonetheless, similar considerations apply to elsewhere in northern Europe and parts of North America. Forestry has become so advanced technologically and in terms of the infrastructure that the ever-diminishing work force can manage the entire area of 20 million ha of forested land in Finland, practically down to the level of single big trees. With around 140,000 km of forest roads, or on average 0.7 km for every square km of forested land, practically the entire forested land is within the reach of I. Hanski (&) Department of Biological and Environmental Sciences, University of Helsinki, P.O. Box 65, Helsinki FI-00014, Finland e-mail: ilkka.hanski@helsinki.fi