Bioengineering with willow to mitigate the impact of permafrost along the Alaska Highway
In Yukon, much of the permafrost is less than a degree below freezing and sensitive to heat flow from the surface. Heat flow to permafrost results in excess soil water. The thaw – freeze cycle results in damage to highway infrastructure. Woody species have the ability to remove significant amounts of water from the soil through transpiration (water uptake through the roots and evaporation from the leaves). Willow (Salix spp.) is a water demanding crop which thrives in wet soils but not water logged soils. Depending on the climate, willow can transpire between 3 and 19 million litres per hectare per year. If willow were planted along highway right of ways, they likely would reduce summer soil water content and reduce the amount of freeze damage the following winter to highway infrastructure.
Willow produces vigorous juvenile growth because it is a pioneer species particularly when it is coppiced (cut back to ground level). Growth rates increase after coppicing as each original shoot produces 5 to 15 new shoots after coppicing. The more willow growth, the more water that is transpired. Coppicing willow in late fall – early winter would promote shoot growth and reduce over winter snow accumulation.
Willow cuttings are harvested when the buds are dormant and placed in cold (~2°C) storage or taken to the nursery for rooting. Cuttings should come from one year old wood for the process to be most successful. Part of the early work will be to determine the most effective method to get willow established on site.
Unfortunately, not all willow species or populations have the same growth habits in wet soils. This means the best source material also needs to be identified if a successful soil water mitigation approach is to be developed. Candidate willow populations will be identified and collected in the spring of 2011. They will be grown in a common garden trial. Growth will be assessed in the fall of 2011 and the selected populations collected in February 2012.
The first challenge in the trial is to get the populations to root and grow on site. Once this is achieved, geophysical assessments of the trial areas will be conducted to determine the efficacy of willow on mitigating permafrost degradation. This will be done in collaboration with Dr. Guy Dore of Laval.
Project Leader: Chris Hawkins, PhD, VP Research, Yukon Research Center, Yukon College
Collaborator: Dr. Guy Dore, Laval University
Collaborator: Paul Murchison, PEng, Department of Highways and Public Works, Government of Yukon
Woodmere Nursery, Telkwa, BC
Adlard Environmental, Charlie Lake, BC
Yukon Research Centre