Planting trees in soils above non-acid-generating wastes of a boreal gold mine

Abstract

Tree planting is a useful means of integrating reclaimed mine sites into natural forested landscapes. The main objective of this study was to evaluate the effect of soil thickness and nature on the establishment and metal accumulation of trees planted in low sulfur mine wastes under boreal conditions. Two field experiments were conducted to evaluate survival, growth, and nutrient and trace metal concentrations of several trees, including 2 fast-growing species (Pinus banksiana, Larix laricina, Populus maximowiczii × P. balsamifera, P. × canadensis × P. maximowiczii, and Salix viminalis), planted in soils (topsoil or subsoil, 50 or 20 cm thick) above waste rock and thickened tailings, respectively. As expected, tree growth increased (×2) in the topsoil compared to the subsoil above waste rock, despite mineral fertilization. Tree growth also decreased in thin topsoils, concomitantly with a decrease in foliar N concentrations, but soil thickness had no effect on tree survival. The basket willow appeared well adapted and multi-purpose for mine-waste revegetation over the short term since its survival remained maximal whatever the nature (topsoil or subsoil) or thickness (50 versus 20 cm) of the soil layer or waste type (waste rock versus tailings). The tamarack showed good survival and growth on both waste types (except in subsoil alone). By contrast, the survival (waste rock) and growth (thin soils above tailings) of hybrid poplars was poor under the tested conditions. On these non-acid-generating wastes with low total trace metal concentrations, none of the tree species accumulated trace metals from soil in their foliage, but basket willow survival should be followed over the longer term to check for deleterious effects of Zn accumulation.