Natural plant colonization of borrow pits in boreal forest highlands of eastern Canada

Plant colonization after gravel extraction for road construction is slow and is often considered to be primary succession. The goal of this study was to identify the plant communities that spontaneously colonized borrow pits located in boreal climate zones and to assess how environmental variables influenced this colonization process. It also helped identifying potential combinations of plants to use as well as environmental factors to improve to restore borrow pits. A total of 505 plots were inventoried in 117 borrow pits located in the boreal forest highlands 120 km northeast of Quebec City, Quebec, Canada (Parc national des Grands Jardins). Species cover was visually estimated for different plant communities within each borrow pit where slope and soil characteristics were also evaluated. We used multivariate analyses, including clustering, redundancy, and regression tree analyses. The borrow pits studied were undergoing primary succession processes decades after abandonment. The main pioneer species were bryophytes and lichens. Soil water content and soil physicochemistry had the greatest influence on the natural colonization of borrow pits. We observed that, based on the prevailing conditions, the bryophytes Polytrichum piliferum Hedw. and Niphotrichum canescens (Hedw.) Bednarek-Ochyra & Ochyra, lichens of the genus Stereocaulon , and the lichen Trapeliopsis granulosa (Hoffm.) Lumbsch could potentially act as nurse species and could initiate the restoration of borrow pits located in boreal forests.