Effects of the seasonal availability of freshly cut logs and tree species on the early response of saproxylic insects in boreal forest

Abstract

Deadwood left on site after logging can be colonized by many saproxylic insects including xylophagous species that can damage the wood. This study aims to estimate the risks resulting from the storage of logs at the edge of balsam fir-white birch stands. We used taxonomic richness, as well as visitation and colonization rates of saproxylic insects to determine how their use of freshly cut logs varies with the seasonal availability of logs and the tree species. During the summer of 2019, balsam fir, black spruce, and paper birch logs were experimentally cut at three different periods and were placed in four harvested sites located in the Forêt Montmorency experimental forest in eastern Quebec, Canada. Visitation and colonization rates were assessed using trunk-window traps and log dissection, respectively. A total of 854 saproxylic insects belonging to 53 genera were captured over the three months of sampling. The logs were colonized by xylophagous species within one month after tree death. These xylophagous insects belonged mainly to the species Urocerus prob. albicornis, and Monochamus prob. scutellatus. Colonization rates of logs by Monochamus prob. scutellatus were higher from mid-July to mid-September than earlier during the season. These xylophagous species also responded to tree species, with higher abundance on conifers than on white birch both in terms of visitation and colonization rates. Furthermore, there was no evidence of colonization on paper birch. Our results suggest that a prompt harvesting of conifer logs between mid-July and mid-September on harvested sites will minimize damage to freshly cut logs.