Site occupancy and spatial co-occurrence of boreal small mammals are favoured by late-decay woody debris

Dwindling stocks of decaying coarse woody debris (CWD), as a result of forest management and growing interest for biofuels, may jeopardize the persistence of a broad spectrum of organisms such as small mammals. In this study, we quantified the effects of CWD in late-decay stages on the occupancy dynamics of small mammals in managed and unmanaged boreal forests. Probabilities of initial site occupancy, colonization, local extinction, and co-occurrence were modelled for five boreal small mammal species. Southern red-backed voles (Myodes gapperi Vigor) and southern bog lemmings (Synaptomys cooperi Baird) were more likely to occupy sites with high volumes of late-decay CWD early in the summer. The probability of local extinction for deer mice (Peromyscus maniculatus Wagner) slightly decreased with an increasing volume of late-decay CWD in harvested sites. Southern red-backed voles and meadow voles (Microtus pennsylvanicus Ord) co-occurred more often in old, uncut forests, as well as harvested sites with high volumes of late-decay CWD. These results suggest that cover provided by late-decay CWD benefited two small rodent species during early reproduction and increased persistence of deer mice later in the summer. Finally, we found that in addition to high live-tree basal areas, high late-decay CWD volume also favours local diversity of small mammals.