Drivers of vegetation regrowth on logging roads in the boreal forest: Implications for restoration of woodland caribou habitat

The worldwide increase in anthropogenic disturbances imposed by the expansion of land use practices has important effects on vegetation dynamics and animal communities. The North American boreal forest is no exception to this global trend, and there are growing concerns regarding the persistence of linear anthropogenic features across Canada because of their negative impacts on wildlife and, particularly, on threatened species such as the boreal caribou. While many recent studies have investigated the state and distribution of regeneration on seismic lines in the western part of the country, few studies have characterized the natural regrowth of logging roads, the main type of anthropogenic linear features found in eastern Canada. As seismic lines and logging roads are structurally different, results from seismic line studies may not be easily generalized to logging roads. In this study, we therefore 1) assessed the influence of different characteristics on vegetation regrowth composition and 2) determined which environmental drivers may compromise natural regrowth on logging roads. We tested these questions using data collected from 56 1-km long road segments distributed in three different regions across Québec’s boreal forest (eastern Canada). We used a canonical correspondence analysis to characterize the species composition of vegetation regrowth on logging roads and used mixed regression models to assess the influence of different biotic and abiotic variables on regrowth establishment. The number of growing degree-days and the proportion of coniferous stands in the surroundings of a road segment explained most of the variation in species composition of the vegetation on roads. Regrowth composition on roads was distributed along a gradient shifting from a high number of alder stems (in the region with a higher number of degree-days) and a smaller proportion of coniferous stands (surrounding the road segment) to a higher number of coniferous stems in regions experiencing less growing degree-days where road segments were surrounded by a greater proportion of coniferous stands. Soil compaction was the most important variable impeding the establishment of vegetation on logging roads. A greater proportion of wetlands surrounding the road segment also contributed to poor regrowth. Our results underline the slow rate of passive regeneration of logging roads and the importance of road surface decommissioning, which should include tree planting, in the context of woodland caribou habitat restoration.