Investigation of ecosystem legacy-based mine reclamation techniques : effects of soil transfers, forest connectivity and plant–soil feedbacks on soil food web recovery and plant establishment

Primary successional post-mining landscapes present physical, chemical and biological barriers to terrestrial ecosystem recovery. I investigated if legacies of the pre-disturbance ecosystem can be applied to help overcome these barriers, leveraging the processes that guide succession following natural disturbances. In a three-year field experiment at the Mount Polley Mine, Canada and in a greenhouse experiment using tailings, overburden and forest soil from the mine, I tested if (1) adding small volumes of forest soil to the seedling rooting zone during planting and (2) spatial connectivity with undisturbed forest would improve soil food web recovery and plant establishment. Soil additions improved seedling growth and/or nutrition in the greenhouse and field, corresponding with greater root colonization by microbial mutualists. In the field, soil additions increased soil faunal diversity and caused bacterial community shifts consistent with advancing succession, with greater benefits in lower quality soils. Sterilized greenhouse controls revealed that a later successional conifer benefited primarily from the biological inoculum, while an early successional shrub benefited more from the improved soil physiochemical conditions. Greater proximity to undisturbed forest increased plant diversity and shifted soil microbial communities, showing that retained patches of intact ecosystems can counteract dispersal limitations. Short-distance belowground connectivity with undisturbed forest improved plant diversity and mycorrhizal fungal community establishment but decreased seedling growth compared to areas “disconnected” with trenches. Field-testing of soil additions and spatial connectivity in conjunction with site preparation showed that application of ecosystem legacies can have additive benefits with reclamation methods targeting soil physical improvements. In a second greenhouse experiment, I tested if plants establishing in mine reclamation materials regenerate soil microbial legacies that facilitate successional advancement. I found negative feedbacks due to fungal pathogen accumulation promoted turnover of an early successional shrub, while formation of distinct mycorrhizal fungal communities selectively promoted establishment and stability of compatible later successional tree species. This reinforces that reclamation plant species selection can influence long-term plant community assembly. Ecosystem legacy-based mine reclamation methods could be used operationally to simultaneously enhance dispersal and establishment of native plants and soil organisms, which, over the long-term, is anticipated to have positive feedbacks on ecosystem recovery.Forestry, Faculty ofGraduat