Plantation of trees in soil layers for the reclamation of non-acid generating wastes of a boreal gold mine

1 Marie Guittonny-Larcheveque, The Research Institute in Mines and Environment - UQAT

The occurring of mines in Canadian boreal forests implies that mine revegetation strategies should aim at establishing trees as an attempt to restore disturbed habitats. But tree growth is frequently impeded on mine wastes. The use of soil layers above the wastes increases tree plantation success. Our main objective was to evaluate the effect of the thickness and quality of soil layers on the establishment and phytostabilisation ability of trees planted in non acid-generating mine wastes under boreal conditions. Two field experiments were conducted to evaluate survival, growth, and nutrient and trace metal concentrations of multispecies plantations, including fast growing willow and poplars, planted in soil layers above waste rocks and thickened tailings, respectively. The basket willow appeared well adapted and multi-purpose for mine wastes revegetation in the short-term since its survival remained maximal whatever the quality (topsoil or mineral soil) or the thickness (50 vs 20 cm) of the soil layer and the waste type (waste rock vs tailings). Hybrid poplars lacked survival (waste rocks) or growth (thin covers above tailings) performances in the tested conditions. On waste rocks, tree growth increased (x2) in the topsoil compared to the mineral soil layer, despite mineral fertilization. On tailings, tree growth generally decreased in thin topsoil layers, concomitantly to a decrease in foliar N concentrations. On these non acid-generating wastes, tree species did not accumulate trace metals except Zn (x2 soil) in willow leaves.