A comparison of three methods to estimate species richness of saproxylic beetles (Coleoptera) in logs and high stumps of Norway spruce

Abstract

AbstractThe amount of dead wood in forests has decreased owing to modern forest practices, and many species associated with this habitat are currently threatened. In Sweden during the last decade, naturally downed logs have been retained and, at clearcuts, high stumps have been artificially created to maintain saproxylic (dead wood dependent) insects. We tested how much these types of dead wood are used by sampling saproxylic beetles in dead wood of Norway spruce (Picea abies (L.) Karst.; Pinaceae) in managed forests in central Sweden. To analyse how surveys should be conducted in these kinds of studies, we compared three methods over an entire growing season. We found that the relationship between the type of dead wood and species richness was statistically significant when we used bark sieving and emergence traps, but not when we used window traps. It is impossible to ascertain whether beetles collected with window traps are related to the type of dead wood on which they are found and, therefore, such traps are less useful in studies of specific substrates. The yield from sieving was highest in spring and autumn, whereas species richness in window trap samples peaked in June and July and that in emergence traps peaked from May to July. With emergence traps we collected, on average, about twice the number of species over the whole season as we did by sieving on a single occasion in the spring. Both emergence trapping and sieving reveal what is present in individual pieces of dead wood, but these methods sample partly different faunas. We found fewer species on artificially created high stumps (on clearcuts); however, these stumps seem to be useful for some red-listed species.