Growing Biomass: Shrub Willow

Introduction of the Crop:

Shrub Willow; also known as Hybrid Willow, is related to nearly 150 willow species worldwide.  This specific species in the Upper Peninsula is mainly cross bred of native and European origins. The cross breeding of these species was done to have a better grasp on growth potential (speed of growth and strength of vegetative propagation) as well as genetic variability (to better protect biological diversity, productivity, and health).

The study and use of Shrub Willow in the United States is exceptionally limited, studied primarily in the State of New York and the State University of New York. However, Shrub Willows is being used in Skandia, Michigan with the establishment of an operational scale Shrub Willow plantation through Traxys Power and Michigan State University (Froese R. & Abbot Z., 2012). Once properly established on a site, this species is able to be harvested in three to four year periods for as many as seven to eight cycles.

Site Selection:

Shrub Willows have site requirements very similar to Hybrid Poplars with a pH range of 5-7 and similar organic matter requirements. However, they are more sensitive to site attributes and may require additional monitoring and manipulation depending on site management.

Site Preparation:

Similarly to Hybrid Poplar, Shrub Willow requires a lack of competition from other plants, either woody in nature or as herbaceous weeds. These competitors have the ability to siphon off nutrients and water that is present on site away from young, freshly established willows. Shrub Willows require herbicide application at the beginning of year one, two and potentially the third depending on weed vigor. Because this species is harvested on a three to four year rotation, the removed woody biomass contains a noticeably higher nutrient load than what would normally be harvested in a conventional sense (such as with Hybrid Poplar or natural stand management).  Even though harvests occur during ?leaf off? portions of the season, not all of the nutrients will be translocated to the root systems for storage (Volk, et al. 2004). This being said, the need to add nutrients to the site following harvest will see an increase in costs to the landowners. When planting Shrub Willow for the first time, densities of stems per acre are noticeably higher than most planting systems for woody vegetation (Hybrid Poplar 1,200 cuttings per acre? Shrub Willow 6,000 cuttings per acre). With densities this high, hand planting is not an option for any harvesting endeavor. The need for mechanical planting and modified agricultural equipment during harvesting to cut and chip the plants will play into higher start-up and harvesting costs for landowners.

End Result:

The managing of land for Shrub Willow provides many positive attributes to landowners. Plantations established on idle lands provide income that would not normally be present. Along with this, the utilization of Shrub Willow plantations by wildlife adds an aesthetic value for migratory birds, game species, and other non-target species. However, the main drawback with growing this crop in the Upper Peninsula is quite simple: the experience with Shrub Willow does not exist in the Midwest. Even though experimental plots are being established, the infrastructure is not present. Going further with this point, no market currently exists for Shrub Willow in the U.P. Nonetheless with future markets moving toward the utilization of biomass, the growth potential of Shrub Willow should not be ignored.

Pros:

  • Plantation grown
    • Tighter spacing in rows, relies on stump sprouts for future harvest
  • First harvest in third to fourth year
    • Harvest in  three to four year cutting cycles
  • Support seven to eight harvests over 25 year lifespan
  • Growth potential nearly as high as Hybrid Poplar

Cons:

  • Start-up costs very high
  • Very sensitive to site conditions
  • Requires fertilizer, herbicide application several years in a row, and after every harvest in some cases
  • Requires modified agriculture equipment for harvest
  • Market nonexistent for Shrub Willow (does not produce pole timber like hybrid poplar)

PDF Downloads

2004 Willow Biomass Crops Study