Decadal effects of emulating natural disturbances in forest management on saproxylic beetle assemblages

Prescribed burning and retention forestry are used to bring the biological legacies of forest harvesting closer to those of natural disturbances. Although widely used, the effects of these methods on species assemblages in the longer term are still relatively unknown. In 2000, we established a large-scale replicated field experiment to explore the effects of prescribed burning and tree retention (four levels: 0, ten and 50 m3 ha− 1 and unharvested control) on saproxylic beetles. Assemblages were monitored over 10 post-treatment years. Our results showed that species richness of predators was increased by burning of the forest stand. Early- and late-stage xylophagous species increased in the first post-harvest year. Increased logging intensity led to a decrease in mycetophagous, early-stage xylophagous and predator species richness over the ten year period. In the burned unharvested stands, the total species richness remained high after ten years, but decreased to the pre-treatment level in the stands with retention trees, and to even lower levels in the clear-cuts. Furthermore, the saproxylic beetle assemblages in the burned unharvested stands differed from the assemblages in any of the harvested stands. Burning increased pyrophilous and rare and red-listed (RRL) species richness. Over the ten year period, the richness of those species collapsed in the harvested stands, but increased in the burned unharvested stands. Our results emphasize the difference in tree stand legacies between logging and natural disturbance, but also indicates that prescribed burning and retention forestry have the potential to alleviate the negative effects of forest management on biodiversity in the longer term.