Facilitating native plant recovery on copper mine tailings in the semiarid grasslands of Southern Interior British Columbia

The semiarid grasslands of interior British Columbia (B.C.) are a unique ecosystem which provides an array of economic and ecological resources, but historic and current human and environmental pressures have led to their decline. Surface mining involves stripping the natural vegetation and topsoil, altering of natural topography, and deposition of waste materials (e.g. tailings and waste rock) at the landscape level. Restoration of natural soil processes and native vegetation communities on such sites is challenging because 1) the mine soils are often characterized by having adverse physiochemical properties such as high metals content, extreme pH, and low organic matter, 2) there are barriers to native seed acquisition and native species do not perform well on nutrient poor sites, and 3) seedling germination and establishment is limited in semiarid environments because of prevailing harsh climatic conditions. The primary objectives at the onset of mine reclamation are to ameliorate the physical and chemical properties of the soils (usually with an organic amendment) and establish a sustainable vegetative cover to prevent wind and water erosion of metals and other harmful contaminants (a process known as phytostabilization). Facilitation by nurse plants and cover crops has recently come to the forefront as a potentially promising practice for restoring natural communities on degraded sites in stressful environments. The objectives of this thesis were to 1) investigate the suitability of locally available organic soil amendments and native bunchgrasses (Pseudoroegneria spicata and Festuca campestris) for reclamation at the Historic Afton Tailings Storage Facility (TSF), near Kamloops, B.C., in a greenhouse study and 2) assess the facilitative effects of soil amendments, Artemesia tridentata nurse plants, and agronomic cover crops on various abiotic and biotic parameters relating to native grassland species establishment at the TSF. In the greenhouse, plants were grown in various ash-compost-wood chip combinations and were evaluated using a randomized complete block design with 13 treatments and 10 replicates. In the field, native plants were seeded in small (1.23 m2) study plots with cover crops and/or planted with nurse plants in amended tailings and assessed in a randomized complete block design with 8 treatments and 3 replicates. The results of the greenhouse study indicated that compost was the most effective amendment, as it effectively ameliorated tailings physiochemical properties and promoted significantly greater seedling production. Analysis of shoot tissue elemental concentrations after 90 d growth determined that both species were not suitable candidates for phytostabilization because they accumulated high amounts of molybdenum. Artemisia tridentata nurse plants appeared to exert some facilitative effects including shading which resulted in lower soil temperatures early in the growing season, but there was also some evidence that they competed for soil moisture. Nonetheless, plant species diversity was higher under nurse plants compared to in the open, which indicated that some facilitative mechanisms may be at play. Cover crops appeared to have a negative effect on native plant establishment which was likely because of their aggressive growth characteristics and increased competition for soil moisture. The findings of this study provide important considerations for mine restoration practices in B.C.’s semiarid grasslands.