Mechanical site preparation and use of non-invasive cover crops influences early-successional forest vegetation composition of a reclaimed airstrip in the Boreal Forest

Abstract

Rebuilding native forest ecosystems after industrial disturbance is key to sustainable resource development. However, self-sustaining forests do not always result from current reclamation practices, mostly due to grass-driven arrested succession. Here we assessed the interactive effects of soil treatment and cover cropping on forest succession in a recently reclaimed airstrip in western Canada. Three surface soil treatment techniques were applied in five block replicates following asphalt removal, soil decompaction, site recontouring and topsoil placement with dozers: no surface treatment (smooth), discing with agricultural disc harrows (disc), or plowing with a RipPlow™ (plow). Within each soil treatment, subplots were then either seeded with Secale cereale (fall rye), a non-invasive annual grass, or left without a cover crop. In the first 5 years after treatment, soil treatment had a much greater impact on the vegetation than cover cropping. Plowing favored tree growth while both plowing and discing treatments supported natural regeneration of seed-banking shrub species and native forb cover when compared to the smooth treatment. The smooth treatment favored grass species (mostly non-native), presumably by allowing them to spread horizontally though it also encouraged higher rates of establishment of wind-dispersed Salix species. In general, the discing soil treatment had intermediate effects on tree growth and vegetation community composition. Secale cereale suppressed non-native weeds during the early stages and disappeared towards the end of the experiment, without hindering the establishment of desirable woody species. We conclude that increasing soil surface variability through the plow treatment tested in the present investigation, and potentially aided by the addition of a non-invasive cover crop, represent a combination of reclamation strategies to promote forest development in heavily disturbed industrial sites.