Substrate comparison for short-term success of a multispecies tree plantation in thickened tailings of a boreal gold mine

Abstract

Tree planting can accelerate the conversion of mine sites into forests after closure, thereby decreasing environmental impacts on forested landscapes. However, few studies have investigated tree planting to reclaim metalliferous mine tailings. To mitigate the restrictions to tree growth associated with mine tailings, soils and amendments can be used. A 2-year field experiment was conducted in low-sulphur thickened tailings of a gold mine under boreal conditions. We aimed to select the best substrate to establish multispecies plantations. We compared the effects of (1) increasing the topsoil volume and thickness, (2) amending tailings and overburden with greenwaste compost, and (3) direct planting in the tailings on the establishment of Larix laricina (Du Roi) K. Koch, Pinus banksiana Lamb., Salix viminalis L., and P. × canadensis Moench × P. maximowiczii A. Henry. Trees did not survive the first winter when planted directly in tailings, but compost addition to tailings increased survival through substrate structure improvement. However, survival and growth remained lower for three species planted in the compost and tailings mixture compared to soil treatments. Tree roots did not colonize tailings underlying the compost and tailings mixture, whereas roots were present in tailings underlying soil layers. In overburden amended with compost, survival and growth rates were similar to those for trees planted in topsoil of the same thickness. Adding compost to tailings or mineral soil improved the P nutrition of trees, which appeared a limiting nutrient in this study. Tree growth was influenced by topsoil thickness (50 vs. 20 cm) rather than volume (20 cm layer vs. 20 cm deep planting holes); trees grown in the thicker topsoil showed the highest N nutrition and aerial growth.