Occurrence patterns of dead wood and wood-dependent lichens in managed boreal forest landscapes
Abstract: Dead wood is a key resource for biodiversity, on which thousands of forest organisms are dependent. Because of current forest management, there has been a large-scale change in dead wood amounts and qualities, and consequently, many wood-dependent species are threatened. The general aim of this thesis is to increase our understanding of habitat requirements and occurrence patterns of wood-dependent lichens in managed, boreal forest landscapes. We surveyed dead wood and wood-dependent lichens in three study landscapes of managed boreal forest in southern Sweden. The observed occurrence patterns of dead wood in the studied landscapes are to a large extent attributable to management practices, with clear-felling as the main driver of dead wood input. Harvesting forest biomass for bio-fuel production will cause wood-dependent lichens species to decline. Coarse woody debris is important for wood-dependent lichens, but stumps, snags and logs host different species assemblages. Snags are rare in managed forest landscapes and increasing the landscape-scale amount of them would benefit wood-dependent lichens. The previously neglected dead wood type of dead branches on living trees make up a large portion of all dead wood available to wood-dependent species in managed boreal forests. Fine woody debris, including both branches on the ground and dead branches attached to living trees, was, however, found to have a low relative importance for wood-dependent lichens. We modeled species abundance in relation to characteristics of dead wood objects and forest stands, and estimated the landscape-scale abundance of wood-dependent lichens. Young managed forests <60 years of age held the largest populations of these species, because such stands contain more coarse woody debris per hectare than older forests or forested mires, and they occupy a much larger total area. Keeping parts of the landscape outside the forestry system is probably necessary to maintain the landscape-scale persistence of dead wood types that are rarely created within standard management regimes. To conserve the most threatened wood-dependent species, it is necessary to find ways to create and maintain dead wood types and qualities that are currently rare in managed boreal forest landscapes.
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