In the Yukon Territory, transmission rights‐of‐way (ROWs) are managed using brushing and mowing techniques alone. When cut, target species such as Populus tremuloides Michx. and Salix spp. grow rapidly shortening maintenance cycles. Long‐term vegetation control may be improved by integrating herbicide application. However, prior to implementation, the dissipation and toxicity of herbicides in northern latitudes needed to be assessed. The dissipation of Garlon XRT (triclopyr) and Arsenal Powerline (imazapyr) in soils was assessed at five ROW locations representative of the main ecoregion types where ROWs occur within the Yukon Territory. Soils from four sites were collected at 1, 30, and 365 d after treatment to determine persistence of herbicides for each of three application methods (backpack spraying, cut stump, and point injection). Increased sampling intervals were added to better determine the dissipation rate of each herbicide in Yukon Territory soils. Soil dissipation data were linked to a series of standardized toxicity tests, including three soil invertebrates (Enchytreaus crypticus, Folsmia candida, and Oppia nitens). Additionally, the dissipation of both herbicides from the target species Salix glauca L. was assessed at one site. Herbicide residues persisted in soils for longer than 365 d after treatment and longer than 30 d after treatment in S. glauca. However, concentrations were below the concentration that would affect 25% of the invertebrate species tested. Weight of evidence and toxic exposure ratios were used to characterize the risks associated with herbicide application in northern latitudes and provided both qualitative and quantitative means to communicate the results to the public. Core Ideas Herbicide use may improve vegetation management along rights‐of‐way in the Yukon. Triclopyr is a good alternative due to a mobile‐phase DT50 of 1 d after treatment. Imazapyr presented no unacceptable risk to the soil invertebrates tested. Risk characterization indicated triclopyr and imazapyr are acceptable in northern latitudes. Triclopyr presents less risk due to fast dissipation and low risk to soil invertebrates.

Effective bioremediation of hydrocarbons requires innovative approaches to minimize phosphate precipitation in soils of different buffering capacities. Understanding the mechanisms underlying sustained stimulation of bacterial activity remains a key challenge for optimizing bioremediationparticularly in northern regions. Positron emission tomography (PET) can trace microbial activity within the naturally occurring soil structure of intact soils. Here, we use PET to test two hypotheses: (1) optimizing phosphate bioavailability in soil will outperform a generic biostimulatory solution in promoting hydrocarbon remediation and (2) oligotrophic biostimulation will be more effective than eutrophic approaches. In so doing, we highlight the key bacterial taxa that underlie aerobic and anaerobic hydrocarbon degradation in subarctic soils. In particular, we showed that (i) optimized phosphate bioavailability outperformed generic biostimulatory solutions in promoting hydrocarbon degradation, (ii) oligotrophic biostimulation is more effective than eutrophic approaches, and (iii) optimized biostimulatory solutions stimulated specific soil regions and bacterial consortia. The knowledge gleaned from this study will be crucial in developing field-scale biodegradation treatments for sustained stimulation of bacterial activity in northern regions.