Restoration of Centennial Wetlands, Sherwook Park, Alberta: Weed Community Composition and Management

Abstract

Centennial Wetlands is a wetland complex located in Sherwood Park, Alberta that consists of multiple natural and constructed cells incorporated into the municipal storm water management system.  In 2012-2013, a new basin was constructed as part of this complex in compensation for a wetland that had been destroyed during development of a new transit and recycling facility nearby.  As part of this construction, an extensive upland area was created between the new basin and a nearby remnant forest.  Municipal environmental managers were interested in examining weed abundance and community composition, and potential non-chemical weed control methods, for the site.  To this end, I established a total of 9 weed sampling and control plots in each of two areas at the site.  These included 3 replicates in each area of control (no treatment), mow, and solarization, for a total of 18 plots.  Sampling was down in all plots during establishment of the study (July 2015) to estimate overall plant community composition and weed abundance.  Sampling was repeated in October 2015, and again in August 2016 to examine changes in weed abundance and community composition in response to treatments.  Mean weed coverage was approximately 39% at project initiation, and seven weed species were present at the site.  Weed cover was reduced by mowing in the first season, but had started to rebound by the end of the second growing season.  Solarization was more effective at reducing weed cover, but I did not track response of the plant communities after removing the plastic sheeting used during the experiment.  However, the effects of this approach are also expected to be transitory, based on other studies.  I recommend that solarization be used to open space for planting and/or seeding native species, and for planting shrubs through the plastic to encourage strong establishment success and enhanced competitive ability.  In addition, although not as effective at reducing weed populations, mowing could be combined with seeding and/or planting at sufficient densities to increase the likelihood of establishment of native species at the site.  It may be necessary to protect these plantings/seedlings from local wildlife, as some species – such as Canada geese – can negatively affect young vegetation and prevent establishment.  Overall, I recommend that municipal staff involved in this project pursue a more coordinated planning and implementation approach to ensure the Centennial Wetlands restoration project is cost-effective and successful.