title: Numerical responses of saproxylic beetles to rapid increases in dead wood availability following geometrid moth outbreaks in sub-arctic mountain birch forest.
abstract: Saproxylic insects play an important part in decomposing dead wood in healthy forest ecosystems, but little is known about their role in the aftermath of large-scale forest mortality caused by pest insect outbreaks. We used window traps to study short-term changes in the abundance and community structure of saproxylic beetles following extensive mortality of mountain birch in sub-arctic northern Norway caused by an outbreak of geometrid moths. Three to five years after the outbreak, the proportion of obligate saproxylic individuals in the beetle community was roughly 10% higher in forest damaged by the outbreak than in undamaged forest. This was mainly due to two early-successional saproxylic beetle species. Facultative saproxylic beetles showed no consistent differences between damaged and undamaged forest. These findings would suggest a weak numerical response of the saproxylic beetle community to the dead wood left by the outbreak. We suggest that species-specific preferences for certain wood decay stages may limit the number of saproxylic species that respond numerically to an outbreak at a particular time, and that increases in responding species may be constrained by limitations to the amount of dead wood that can be exploited within a given timeframe (i.e. satiation effects). Low diversity of beetle species or slow development of larvae in our cold sub-arctic study region may also limit numerical responses. Our study suggests that saproxylic beetles, owing to weak numerical responses, may so far have played a minor role in decomposing the vast quantities of dead wood left by the moth outbreak.
authors.affiliation: Department of Arctic and Marine Biology, University of Tromsø, Tromsø, Norway.
authors.forename: Ole Petter Laksforsmo
authors.initials: OP
authors.lastname: Vindstad
authors.affiliation: Department of Ecology, Leuphana University Lüneburg, Lüneburg, Germany.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Schultze
authors.affiliation: Norwegian Institute for Nature Research, Fram Centre, Tromsø, Norway.
authors.forename: Jane Uhd
authors.initials: JU
authors.lastname: Jepsen
authors.affiliation: Norwegian Institute for Nature Research, Fram Centre, Tromsø, Norway.
authors.forename: Martin
authors.initials: M
authors.lastname: Biuw
authors.affiliation: Department of Arctic and Marine Biology, University of Tromsø, Tromsø, Norway.
authors.forename: Lauri
authors.initials: L
authors.lastname: Kapari
authors.affiliation: Norwegian University of Life Sciences, Department of Ecology and Natural Resource Management, Aas, Norway.
authors.forename: Anne
authors.initials: A
authors.lastname: Sverdrup-Thygeson
authors.affiliation: Department of Arctic and Marine Biology, University of Tromsø, Tromsø, Norway.
authors.forename: Rolf Anker
authors.initials: RA
authors.lastname: Ims
mesh_terms: D000818:Animals; D001110:Arctic Regions; D029662:Betula; D001517:Coleoptera; D017753:Ecosystem; D065928:Forests; D005843:Geography; D009036:Moths; D009664:Norway; D011156:Population Density; D014934:Wood