Forest topsoil salvage and placement threshold depths for boreal forest revegetation as influenced by ecosite and substrate texture.

Forest topsoil is a critical source of native vegetative propagules and seeds for boreal forest land reclamation. However, optimal handling practices for this material and its interactions with underlying substrates remain poorly defined. This field study investigated effects of operational topsoil salvage and placement depths on native plant establishment, accounting for site conditions, substrate type, ecosite characteristics, and local climate. We evaluated varying salvage and placement depths across mineral and peat-mineral mix substrates. Shallow salvage (10 cm) maximized plant species richness, density, and canopy cover, particularly when derived from fine texture soils. Conversely, salvage depths greater than 30 cm significantly diluted the propagule bank and reduced plant establishment. Upon placement, deeper applications (10 cm) generally improved native vegetation metrics and helped suppress competitive, less desirable species originating from peat-mineral substrates. Very shallow placements (<5 cm) on sloping sandy substrates were highly susceptible to water erosion. Ultimately, to optimize native plant establishment, reclamation strategies must account for the complex interactions among handling depths, source ecosites, and placement substrates. When topsoil availability is not limiting, shallow salvage combined with deeper placement is recommended to maximize in-situ propagule viability, although further investigation is required to evaluate the efficacy of shallow placement depths at an operational field scale.