Abstract
Intensive forest management has drastically reduced the amount and diversity of dead wood resulting in population decline of saproxylic species. Forestry practices can also disrupt spatiotemporal continuity of dead wood habitats. We studied the effects of stand- and landscape-level densities of host trees on the incidence (proportion of occupied trees) of saproxylic beetles inhabiting recently dead standing Scots pines, a common host-tree type both in natural and managed boreal forests. We compared the occurrence patterns of eight rare specialist and eight common generalist species. Saproxylic beetles were collected from a total of 315 trees in 67 forest stands, including both managed and natural forests, located in three regions which form a gradient in forest-use intensity. Species richness of the entire community at tree and stand level did not respond to the stand- and landscape-level host-tree density. The incidence of six common generalist species did not depend on the stand-level host-tree density, whereas the incidences of four rare specialist species increased with increasing host-tree density. Five out of eight rare specialist species were either significantly less common or absent from the region with the lowest landscape-level density of host trees. We conclude that rare specialist species living in recently dead pines are susceptible to changes in spatiotemporal dynamics of their host trees. To conserve rare early-successional species, it is necessary to ensure continuous input of dying trees by prolonging rotation times in mature forests, regenerating stands using seed-tree cutting and leaving as many permanent retention trees as possible.
Highlights
Dead-wood amount and diversity in many forest ecosystems worldwide are largely controlled by timber production
We conclude that rare specialist species living in recently dead pines are susceptible to changes in spatiotemporal dynamics of their host trees
We studied how the density and continuity of suitable host trees affects the occurrence of eight rare specialist and eight common generalist saproxylic beetles at the stand and landscape scales
Summary
Dead-wood amount and diversity in many forest ecosystems worldwide are largely controlled by timber production. In Fennoscandia, intensive forest management has reduced the amount and heterogeneity of dead wood in boreal forests (Ostlund et al 1997; Jonsson et al 2016) and has affected the spatiotemporal dynamics of dead wood (Stokland et al 2012). A large number of saproxylic species living on dying and dead trees has declined (Siitonen 2001). Loss of suitable host trees will first reduce the fraction of host trees that is occupied (Andren 1996; Hanski 2005). When the density of host trees declines below a speciesspecific threshold value, the extinction threshold, the metapopulation cannot persist in the long term (Hanski 1999). For a metapopulation living in a habitat network, there should be enough spatially connected habitats available both locally, at the stand scale, and at larger spatial scales (Hanski 1999)
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