Factors affecting ecosystem recovery after placer mining in northwestern British Columbia

This research sought to determine the attributes affecting unassisted ecosystem recovery after placer mining. Ninety post-mining sites in 14 creek drainages east of Atlin Lake, British Columbia, were sampled to represent a range of times since disturbance (9 to 76 years). The six indicators utilized (vascular species richness, plant community similarity to undisturbed reference sites, summed plant cover, structural diversity, A-horizon depth, wildlife activity) exhibited different recovery trajectories and dependencies. Across all six indicators, the factors most important to ecosystem recovery were, in order of importance: time since disturbance, microsite relief, elevation, slope position, and soil texture. Without any reclamation, linear extrapolation indicates that a mean of 101 years would be needed for disturbed sites to return to mean undisturbed conditions. Classification and regression tree analysis identified thresholds of these factors that may promote or hinder recovery. These thresholds were used to refine recommendations for promoting ecosystem recovery after mining.