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 for a novel successional trajectory is high. To address a lack of understanding of long-term successional trajectories of reclaimed oil and natural gas well sites in forested lands, we sampled plant community composition and soil attributes on 30 reclaimed and adjacent reference sites in Alberta’s boreal forest ranging from 7-48 years post-disturbance. Our three study objectives were to: i) measure above- and below-ground ecological properties to determine if certified reclaimed wellsites were on a positive successional trajectory for recovery, ii) determine which properties were significantly influenced post wellsite reclamation and were thus good ecological indicators for recovery, and iii) examine changes in plant trait composition among wellsite ages. We used a variety of multivariate statistical analyses (as described in results below) to achieve our three study objectives.
Results/Conclusions
Multi-response permutation procedures and non-metric multidimensional scaling illustrated separation between reclaimed and reference sites plant community compositions. When accounting for forest type, seral stage, and time since last disturbance, there was further separation of sites, with only two sites (7%) resembling community structure of reference sites, and 18 sites (60%) resembling treeless grasslands, two of which were >35 years post disturbance, indicating an arrested recovery trajectory. The remaining 33% of sites are likely on a positive trajectory towards recovery. We used a joint generalized estimating equation (JGEE) to determine if reclamation had a significant effect on soil bulk density and pH, noxious plant cover, canopy cover, grass cover, woody debris, LFH, introduced plant richness, and live tree basal area. Using perMANOVA and Gower dissimilarity index to measure multi-trait functional dissimilarity, we found an overall directional change in plant functional composition with time since reclamation towards that observed in reference sites, but while heading in the 'right' direction, reclaimed sites remained statistically significantly different from reference sites. Overall, our data indicate the anthropogenic disturbance impacts of well pads can be long lasting and may remain for half a century or more post reclamation, potentially flat lining the plant community and functional recovery trajectory of these reclaimed sites.