Summary1. Priority effects have been hypothesized to have long-lasting impact on community structure in natural ecosystems. Long-term studies of priority effects in natural ecosystems are however sparse, especially in terrestrial ecosystems. 2. Wood decay is a slow process involving a high diversity of insect and fungus species. Species interactions that drive change in communities of insects and fungi during wood decay are poorly understood because of a lack of sufficient long-term studies. 3. In this paper, we followed the colonization and succession of wood-living insects and fungi on cut trees during 15 years, from tree death and onwards, in a boreal forest landscape. We test the long-term priority effects hypothesis that the identity and abundance of species that colonize first affect the colonization success of later-arriving species. We also hypothesize that species interact in both facilitative and inhibitory ways, which ultimately affect habitat quality for a red-listed late-succession beetle species. 4. Possible causal associations between species were explored by path analysis. The results indicate that one bark beetle species, Hylurgops palliatus, and one wood-borer species, Monochamus sutor, which colonized the wood during the first year after cutting, influenced the occurrence of a rare, wood-living beetle, Peltis grossa, that started to emerge from the stumps about 10 years later. The positive effects of Hylurgops palliatus and negative effects of M. sutor were largely mediated through the wood-decaying fungus species Fomitopsis pinicola. 5. The study shows that variable priority effects may have long-lasting impact on community assembly in decaying wood. The study also exemplifies new possibilities for managing populations of threatened species by exploring links between early, well-understood species guilds and late, more poorly understood species guilds.

Intensive forest management has led to a population decline in many species, including those dependent on dead wood. Many lichens are known to depend on dead wood, but their habitat requirements have been little studied. In this study we investigated the habitat requirements of wood dependent lichens on coarse dead wood (diameter [10 cm) of Scots pine Pinus sylvestris in managed boreal forests in central Sweden. Twenty-one wood dependent lichen species were recorded, of which eleven were confined to old (estimated to be [120 years old) and hard dead wood. Almost all of this wood has emanated from kelo trees, i.e. decorticated and resin-impregnated standing pine trees that died long time ago. We found four red-listed species, of which two were exclusive and two highly associated with old and hard wood. Lichen species composition differed significantly among dead wood types (low stumps, snags, logs), wood hardness, wood age and occurrence of fire scars. Snags had higher number of species per dead wood area than logs and low stumps, and old snags had higher number of species per dead wood area than young ones. Since wood from kelo trees harbours a specialized lichen flora, conservation of wood dependent lichens requires management strategies ensuring the future presence of this wood type. Besides preserving available kelo wood, the formation of this substratum should be supported by setting aside P. sylvestris forests and subject these to prescribed burnings as well as to allow wild fires in some of these forests.

Including both economic costs and biological benefits of sites in systematic reserve selection greatly increases cost-efficiency. Nevertheless, limited funding generally forces conservation planners to choose which data to focus the most resources on; therefore, the relative importance of different types of data must be carefully assessed. We investigated the relative importance of including information about costs and benefits for 3 different commonly used conservation goals: 2 in which biological benefits were measured per site (species number and conservation value scores) and 1 in which benefits were measured on the basis of site complementarity (total species number in the reserve network). For each goal, we used site-selection models with data on benefits only, costs only, and benefits and costs together, and we compared the efficiency of each model. Costs were more important to include than benefits for the goals in which benefits were measured per site. By contrast, for the complementarity-based goal, benefits were more important to include. To understand this pattern, we compared the variability in benefits and in costs for each goal. By comparing the best and the worst possible selection of sites with regard to costs alone and benefits alone for each conservation goal, we introduced a simple and consistent variability measure that is applicable to all kinds of reserve-selection situations. In our study, benefit variability depended strongly on how the conservation goal was formulated and was largest for the complementarity-based conservation goal. We argue that from a cost-efficiency point of view, most resources should be spent on collecting the most variable type of data for the conservation goal at hand.

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