Long-term effects of high and low intensity partial cutting on saproxylic beetle communities in aspen-dominated stands of the eastern boreal mixedwood forest

Natural disturbance-based management uses partial cutting to maintain stand structure, canopy cover and continued source of deadwood and been widely advocated to better maintain biodiversity in managed forest landscapes. We evaluated whether saproxylic (deadwood-dependent) beetle communities recovered after two decades in aspen stands that have regenerated from 1) clearcutting (CPRS), 2) clearcutting with a prescribed burn, 3) dispersed partial cuts where 2/3 of trees were removed, 4) dispersed partial cuts where 1/3 of trees were removed and 5) uncut stands (control). This study was part of the SAFE experiment (Sylviculture et Aménagement Forestiers Écosystemique) in the Lac Duparquet Teaching and Research Forest (FERLD) in the boreal mixedwood region of Western Quebec, Canada. We collected 301 saproxylic species (5902 beetles) in 2019 using IBL flight intercept traps and compared differences in catch rate, rarified species richness and composition among harvesting treatments. Twenty years post-harvest, saproxylic beetle abundance remained higher in uncut stands and 1/3 cut stands than in 2/3 cut stands, and clearcut stands with and without prescribed burning. Species richness was higher in uncut and partial cut stands than in clearcut stands. Our results suggest that clearcuts and partial cuts with little standing retention have persistent and lasting impacts on saproxylic insects for decades. These lasting impacts may be attributable to patterns of fungal biodiversity in response to cutting. Partial cuts with more standing retention will senesce and fall over longer time scales than stands with less or no retention thus maintaining continuity of relatively fresh deadwood for saproxylic insects.