Tree retention in boreal pine forest

Sammanfattning: Tree retention forestry aims at increasing structural diversity in managed forests. In this study, I have investigated the influence of tree retention forestry on delivery of two ecosystem services (wood production and carbon sequestration) and dead wood (as a proxy for biodiversity). Furthermore, habitat requirements of lichens dependent on dead wood were investigated. The study was conducted in 15 Scots pine forest stands with five various tree retention levels, in which four categories of trees were retained at similar proportions: green living trees, girdled trees, high-cut stumps and cut trees left on the ground. Three additional stands were left untouched (control stands). This thesis consists of three studies. In the first, we investigated how tree retention influences the amount and diversity of dead wood and affects economic costs and revenues. In the second, we simulated outputs of merchantable wood, dead wood and carbon stock at stand and landscape scales. At landscape scale, we simulated the dead wood volumes and carbon stock during a 100-year forest rotation period, keeping landscape size and productivity constant while varying forest management type and amount of land dedicated to conservation (set-aside forests). In the third study, we investigated how dead wood types (low stumps, snags, logs), wood hardness, wood age and occurrence of fire scars influence the occurrence of dead wood-dependent lichens. We found that increased retention level leads to diminished incomes from wood production, decreased logging productivity, decreased level of dead wood destruction, and a higher volume and diversity of dead wood. Furthermore, increased retention level promotes carbon storage at the stand scale. The stand-scale simulations showed that different retention levels have a large influence on the long-term delivery of ecosystem services. However, if wood production was maintained at a constant-level among landscape-scale simulations, differences in the other outcomes were generally small. The lichen species composition differed significantly among the investigated substrates. Many species were highly associated with old and hard wood (i.e. kelo wood), a rare wood type in managed forest. The findings of this thesis could be used to guide future forest management plans.