Impacts of summer versus winter logging on understory vegetation in the Chequamegon-Nicolet National Forest

In seasonal climates the timing of logging operations can be adjusted to avoid the major growing periods of understory plants and seedlings. We evaluated the understory vegetation at five pairs of hardwood-dominated sites in northern Wisconsin, U.S.A. where one site in each pair was logged during winter and the other during summer. All sites were dominated by sugar maple (Acer saccharum) and basswood (Tilia americana), with varying amounts of other native tree species. Most (84%) of the 247 vascular plant species recorded during the study are indigenous to the region. Winter-logged sites supported significantly higher numbers and percent cover of ecologically vulnerable native plant species as defined by independently established coefficients of conservatism. These differences between winter-logged and summer-logged sites suggest that winter logging may have fewer negative impacts than summer logging on vulnerable plant species and, in the long run, may help maintain plant biodiversity in managed forests of this region. In both types of sites, understory plant richness and diversity were significantly higher near logging roads, due largely to higher numbers of alien species and early successional native plants. Away from roads, neither species richness nor diversity differed between winter-logged and summer-logged sites. Studies that fail to account for differences in species composition and studies that fail to include samples of access roads or skid trails are likely to ignore important impacts of logging activities.