Small mammal responses to coarse woody debris distribution at different spatial scales in managed and unmanaged boreal forests

Dead wood such as stumps and logs found on the forest floor is a key structural element that is used by a broad spectrum of organisms and contributes to soil nutrient cycling. The complexity of the forest floor in the boreal forest is largely dependent on coarse woody debris (CWD), but actual forestry practices may compromise the future recruitment of this resource. The main goal of our study was to determine the effects of CWD on small mammals in stands of varying green-tree retention levels. Since small mammals are associated with microhabitat components at multiple spatial scales, our secondary goal was to assess the effects of scale on small mammal relationship with CWD. Five trapping sessions were conducted in the boreal forest of western Québec, Canada during the summers of 2009 and 2010 in four managed forest blocks. Each block was composed of 12 independent trapping grids equally distributed in three treatments: clearcuts (0% green-tree retention), partial cuts (30% green-tree retention) and controls (undisturbed). We live-trapped small rodents and used pitfall traps for shrews in trapping sub-grids (fine-scale; 50 m) nested in larger grids (stand-scale; 300 m). Southern red-backed vole (Myodes gapperi) and deer mouse (Peromyscus maniculatus) abundances were positively associated with sites with high volumes of well decayed CWD in all treatments, at the fine-scale. Southern bog lemming (Synaptomys cooperi) abundance was positively associated with well decayed CWD, at both scales, but mainly in clearcut areas. Masked shrew (Sorex cinereus) abundance increased with high volumes of well decayed CWD in clearcuts but only at the stand-scale. In contrast, meadow voles were more abundant in sites with high volumes of well decayed CWD in controls than in sites with small volumes at the stand-scale. Patches of partial cuts with high volumes of well decayed CWD were characterized by high abundances of red-backed voles and this clearly indicates that volume and decay of CWD are important drivers that can mitigate the impacts of tree removal. We found different scale-dependent responses of small mammals to volumes of well decayed CWD, which indicates that associations were found at the individual as well as at the population level. We suggest that partial cuts composed of regularly distributed patches of high volumes of CWD (⩾11.4 m3 in patches of 0.03 ha) might have a high potential to maintain red-backed voles, a species associated with mature forests.

► Boreal small mammals are positively associated with well decayed CWD, considering two spatial scales.
► Abundance of small mammals depends mainly on CWD on late decay classes.
► Patches of partial cuts with high volumes of well decayed CWD offer high quality microhabitats for red-backed voles.
► High volumes of well decayed CWD can mitigate the negative impacts of tree removal.
► Availability of CWD has the potential to explain variations in the responses of small mammals to sylvicultural operations.