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.
