, 2009) and thus we assumed that aspens surveyed on clearcuts

reflect the species composition of the harvested forest. Tree retention has only been practiced large-scale for 15–20 years in Northern Europe, thus the choice of time span. We addressed five questions: (1) Is species richness higher on trees exposed for 10–16 years than on trees exposed for 0–4 years, as predicted from the intermediate disturbance hypothesis? (2) Are red-listed species more common on aspens exposed for 0–4 years, as expected based on conservation strategies which stress the importance of aspens in old-growth forests for lichen preservation? (3) Do sensitivity to light, photobiont and dispersal mode of species differ between clearcuts and young forests? We expected

an increase in lichens adapted to open environments and a decrease in lichens sensitive to light, Gefitinib in vivo a decrease in cyanolichens since many of them are reported as old-growth specialists, and an increase in spore-dispersed species since they are considered easily dispersed; (4) Are there species characteristic of clearcuts and young forests, respectively? We expected to identify such species due to assumed differences in life history traits and species ecology; and (5) How large is the regional species pool of lichens growing on aspen, and how many species are found on the 720 aspens find more surveyed here? A total pool of about 90 lichen species has been estimated for boreal Sweden (Gustafsson and Ahlén, 1996), and since our study area was confined to a limited part of the region, we predicted a somewhat lower number. Due to the large number of trees, our forecast was that a substantial part of the species pool should be included in our sample. The study was conducted in an area including the eastern part of Jämtland and western part of Västernorrland counties (Fig. 1) in central Sweden, in the middle and Northern boreal zones (Ahti et al., 1968). The western part of Jämtland was omitted since it has a distinct humid climate and an oceanic lichen flora (Ahlner, 1948). Estimated mean GPX6 precipitation

in the area is 600–800 mm/year whereof 30–40% is as snow. The average temperature in January ranges from −10 °C to −8 °C and in July from 13 °C to 15 °C (Raab and Vedin, 1995). Within the study area, all suitable stands on land owned by the forest company SCA were visited in the field. A suitable stand was clear-felled 0–4 or 10–16 years earlier, and had at least 30 retained, living aspens (diameter at breast height >10 cm). Twenty stands that fulfilled these criteria were found, with an additional four stands on private land, and leading to a total of 12 stands in each age-class (Table 1). A clearcut (0–4 years) was characterized by an open stand with both solitary and aggregated retention trees. The young forest (10–16 years) had larger variation in vegetation height, but the average tree height was still considerably lower than in an old forest.