LAUSR

Abstract Site preparation for oil and gas extraction often requires the complete removal of vegetation and surface soil on the well pad. Although subsequent reclamation then attempts to restore vegetation and soil properties on the well pad, given the magnitude of the extraction disturbance, the potential to shift its successional trajectory is high. The objectives of this study were to: i) assess successional recovery of vegetation and soil on decommissioned and reclaimed well pads and compare it with reference forest of varied successional stages, and ii) identify which above- and below-ground properties were influenced by reclamation and are thus useful ecological indicators for recovery towards forest. We sampled 30 study units in Alberta’s boreal forest; each site included a reclaimed well pad and adjacent reference site, with well pads ranging from 7 to 48 years post-reclamation. We conducted multivariate statistical analysis using 62 ecological above- and below-ground properties (e.g., percent cover of plant species, soil bulk density) categorized by: site type (reclaimed vs reference), natural subregion, forest stage, forest type, and time since reclamation. By grouping sites by site type, forest type, forest stage, and time since last disturbance, there was a clear separation of sites, with only two reclaimed well pads (7%) resembling plant community composition of reference areas, and 18 well pads (60%) resembling treeless grasslands, two of which were > 35 years post disturbance, indicating an arrested recovery trajectory. The remaining 33% of well pads are likely on a trajectory towards recovery. We found that reclamation had a significant effect on soil bulk density (E = 0.35), soil pH (E = 0.24), noxious plant species (E = 2.33), canopy cover (E = −0.26), grass cover (E = 0.16), woody cover (E = −0.18), LFH depth (E = −0.15), introduced species richness (E = 0.26), and live tree basal area (E = −0.17) after controlling for forest stage and time since disturbance. Our results indicate well pad impacts can be long lasting and may remain for decades or more post reclamation, potentially arresting their recovery trajectory.