Optimizing Weed Control

The overall goal of this project was to assess whether noxious weeds managed in the boreal forest are significantly impacting boreal succession, using publicly available literature, available vegetation survey data and field experience of oil sands operations practitioners. Current regulations require control or eradication of noxious/prohibited noxious weeds, presently accomplished with herbicides and manual labour. This project explored whether, under certain conditions, there is a third alternative – utilizing successional processes and forest vegetation development to address some of the issues raised above. Objectives were to: (1) compile information on weed status and management programs for mining and in-situ oil sands operations; (2) determine risk factors for regulated weeds using (i) compilation of fact sheets, (ii) a retrospective case study on available data sets, and (iii) the development of a risk analysis framework; (3) determine whether current approach to weed management of regulated weed species is necessary in reclaimed sites or if other methods could be used; and (4) to identify whether there is enough evidence to reduce the number of weeds requiring active management in the boreal ecosystem.

Correlation analyses across six reclamation sites did not find strong evidence of a negative association between woody cover and noxious weeds (by group or by species) across multiple years of measurement. The only significant correlations were positive associations. This analysis was supported by changes in relative dominance favoring woody vegetation as individual sites aged. However, relative dominance of noxious weeds varied over time with no consistent trend amongst sites. These results suggest active noxious weed management may not be required, as species evaluated did not appear to hinder woody vegetation development; however, it should be noted that the analyses were not causal. Future studies are needed to: (i) confirm noxious species are not overtly competitive with woody vegetation recovery (or to identify specific thresholds that woody vegetation are able to tolerate) and (ii) examine longer term site recovery to confirm noxious species do consistently fall out of these sites. A risk analysis framework was developed based on these results and a currently available risk analysis tool. It was not useful for determining effects thresholds but has utility for its core purpose (to triage and prioritize invasive species in terms of management considerations).