Living snow fences with shrub willows
Blowing snow is a problem on Minnesota roadways and can lead to increased accidents, travel time, salt applications, plowing, and overall high snow removal costs.
Living snow fences (LSFs) are shrubs, trees or plants that form a wind barrier disrupting the wind, causing snow to be deposited on the upwind and downwind sides of the planting. LSFs have been shown to be economically viable solutions for mitigating blowing snow on roadways. The Minnesota Department of Transportation (MnDOT) has identified close to 1,200 miles on MN roadways where blowing snow is a problem. Of these problem areas, 20 miles have been addressed by landowner adoption of LSFs. To encourage wider adoption of LSFs, MnDOT offers incentive payments and assistance for landowners. One plant that has been shown to be effective are shrub willows.
Science, design and placement
Typically snow drifts will collect 10 times the height of the planting on the downwind side. Therefore a 10 foot willow could cause drifting downwind up to 100 feet. Use a proper set back based on winter climate data for the potential snow transport to the site that can be determined with the Climate Design Tool.
A setback range of 100 to 200 feet from the highway right of way is common. Determine the proper width and number of rows to be planted. Extend planting length of the LSF further out on one end may be required to mitigate drifting problems around the end (edge affect). This edge affect planting extension is determined by the Climate Design Tool.
Downwind draft length is function of the capacity/transport ratio. Capacity is primarily driven by height. Fast growing willows can have massive snow catching capacity and reduced drift length shortly after planting.
Shrub willows can provide multiple benefits for humans and the environment. Willows can be cut and used for bioenergy, and decorative florals (pussy willow, etc.) or multiple products. Nurseries usually sell willows as bare root stock or sticks for larger plantings. The recommended source of planting stock is Double A Willow who supplies cuttings of cultivars developed for rapid growth, plant form favorable to LSFs, and pest resistance. These sticks are 8 to 12 inches long.
Shrub willow stems can be cut from native willows in your area or purchased as sticks or bare root plants from nurseries or Soil and Water Conservation District Offices.
Shrub willows planted for a living snow fence are typically planted in a single row at one foot plant spacing or an offset double row at two foot plant spacing with 20 inches between rows. Spacing is usually 2.5 feet between rows and 2 feet apart within the row. Barefoot plants and sticks can be planted with a pull behind tree planter or by hand. Soil preparation and weed control is critical to the survival and rapid growth of young willows. Perennial weeds or grass may be treated before and after tillage with systemic herbicides. Weeds may need to be controlled for the first two years. Biodegradable fabric weed mats can slow weed growth around the seedling but needs to be cut in an X pattern (around the willow) so it does not girdle the willows.
Cutting or coppicing on a regular basis (every 2 to 5 years) can revitalize the plants but is not required.
Willow snow fence research practices and findings
(2013 – 2016 Waseca, MN)
- Willows were coppiced (cut at the base) after the first growing season to generate multiple stems. This is a standard practice for growing willows.
- Willows in the LSF demonstration had average heights of approximately 1 m (3.3 ft) one growing season after coppice. The average optical porosity (the percentage of open space) in willows was 89%. (50% porosity is optimum which could be reached the 2nd year) Height and porosity are both important predictors of the snow trapping effectiveness of snow fences.
- All willow varieties and planting arrangements (2 and 4 rows) were observed to be capturing snow after one growing season post-coppice (2014-2015 winter). The average amount of snow caught by the willows was around 2.5 metric tons per linear meter of snow fence.
- Four-row arrangements tended to catch about 20% more snow than two-row arrangements during the 2014-2015 winter. This was likely due to lower porosity values (i.e., denser shrubs) in the four-row arrangements.
- No significant difference in snow capture was found among the three willow varieties used in the experiment. All varieties produced multiple, small-diameter stems and had similar porosity values. This suggests that multiple willow varieties/species adapted to similar growing conditions could be incorporated into LSFs.
- Based on climatological models, the snow storage capacity of the willow LSFs one growing season post- coppice did not yet exceed the average amount of blowing snow at the study site. However, willow growth models predicted that after the following growing season (2nd growing season) they would be able to exceed the average amount of blowing snow. Therefore, the willow LSF could potentially trap all of the blowing snow before it reaches the road.
- In the variety experiment, all willow varieties exceeded the growth of the traditional LSF species (American Cranberry, Gray Dogwood).
- One native willow, Salix petiolaris, had similar growth to the top performing bioenergy willows, “Fish Creek” and “Oneonta.” This suggests that native willow shrubs may be just as suitable as bioenergy willows for LSFs.
- Extension Agroforestry (Willow LSF research project)
- Snow control tools LSF Design Tool
- MnDOT Living Snow Fence
- Living snow fence: Function and benefits (fact sheet)
- Specialty Forest Products Nebraska Forest Service
- Decorative willows retail nurseries
- The willow project at SUNY-ESF
- Living snow fences show potential for large storage capacity and reduced drift length shortly after planting (1.20 MB PDF)
- KSTP Story on the Hybrid Willow Research at the University of Minnesota
- Roads and Bridges article on Hybrid Willow Research at the University of Minnesota
Gary Wyatt, firstname.lastname@example.org
Diomy Zamora, email@example.com
Mike Reichenbach, firstname.lastname@example.org
Dean Current, email@example.com
Eric Ogdahl, University of Minnesota, Research Assistant
Tim Volk, State University of New York (SUNY)
Justin Heavey, State University of New York (SUNY)
Dan Gullickson, MN Department of Transportation
Gregg Johnson, University of Minnesota, Agronomist, Waseca