Divergent Pathways of Successional Recovery for In Situ Oil Sands Exploration Drilling Pads on Wooded Moderate-Rich Fens in Alberta, Canada

Peatlands in northern Alberta, Canada, are being rapidly impacted by oil sands activities, with potentially long-term consequences for their recovery. In situ oil sands extraction requires exploration of oil resources on a dense network of drilling pads across the landscape. This study examined the recovery of wooded moderate-rich (WMR) fens 10 years after abandonment of these sites with minimal restorative measures. Bryophyte and vascular plant diversity, site microtopography, and water chemistry were assessed on drilling pads and in adjacent areas of undisturbed reference habitat. WMR fens affected by drilling activities were divided a priori into two groups based on strongly divergent trends in their successional development. One group represented the majority of WMR fens observed on the land base; at these sites hummock-forming mosses including minerotrophic Sphagnum species were infrequent and tree recruitment was almost absent. The other group was dominated by Sphagnum species, had Picea mariana and Larix laricina recruitment, and appeared to recover more quickly. Both groups had high abundance of wetland sedges, notably Carex aquatilis. Further, drilling pads belonging to the first group had a high water table, limited elevated microsites, and had surface flooding over a portion of the growing season, in contrast to Sphagnum-dominated sites. Development of the aquatic, bryophyte-poor wetland type is comparable to early stages of wetland succession and these systems will recover relatively slowly, likely from decades to more than a century. Restoring part of the vertical distribution of micro-habitats before abandonment of these pads could stimulate the successional recovery of vegetation.