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Growing woody biomass

Coppice cropping has been used in Sweden since the 1970s to produce biomass, and it’s now gaining attention elsewhere in Europe and in places like the United States, New Zealand, and Canada. Intensive willow coppice cropping seems like an efficient way to produce a consistent supply of purpose-grown fibre. As for any crop, however, there’s a lot to learn about best management practices to achieve its economical production. 

To this end, the Canadian Wood Fibre Centre (CWFC), part of the Canadian Forest Service, began a long-term project in 2005 to evaluate the potential of willow and other woody biomass as intensively managed crops on moderate- to high-quality agricultural land under Canadian growing conditions. “We have a national network of sites that covers most of Canada,” says Derek Sidders, CWFC regional coordinator. “It’s primarily in the areas that have the best potential for this land management to take place—Quebec, Ontario, and the Prairie provinces. We’ve planted demonstration sites across the agricultural range in these provinces to demonstrate the different management options and to look at the input costs and production.”

In addition to the coppice system, which Sidders calls “concentrated biomass,” the project is evaluating two other systems: an afforestation regime and a hybrid arrangement of modified concentrated biomass and afforestation. The aim is to compare the productivity and economic efficiency of the methods, as well as of different species and clones, in the various regions of Canada so that producers can use that information to make informed decisions.  The choice of design could also depend on the final use objectives, says Sidders. 

The concentrated biomass system produces a lot of juvenile wood, with a high ratio of bark to white wood, which could be used for bioenergy and possibly pharmaceuticals or food extracts. In this system, willow or hybrid poplar are grown at very high densities of about 14,800 to 15,600 plants/ha and harvested every three or four years for a total of five to seven harvests. Afforestation, in contrast, involves growing hybrid poplar or aspen at lower stand densities that approximate natural densities of about 1,100 plants/ha, says Sidders. Although there is only a single harvest of trees after 15 to 20 years, the larger stems and branches give more output value options such as carbon sequestration and primary forest products, as well as bioenergy. 

The hybrid combination, which is Sidders’ own invention, is designed to maximize the use of space and allow for some short-term revenue under an afforestation scenario. In this system, hybrid poplar is grown with four times the number of trees as in afforestation, that is, with an extra row of trees between each row in the afforestation scenario in both directions. After five years of growth, every other row is harvested. The remaining trees are left to grow for another 10 to 15 years before the final harvest. 

Looking at production efficiencies
This type of study is not for the hasty or impatient. One full cycle of about 20 years will be necessary to fully understand and compare the various methods—their productivity, economics, and market applications. So the CWFC works with various long-term site partners who are interested in the project and its outcome.

One of the study sites is located at the University of Guelph, Guelph Turfgrass Institute (GTI) in Ontario. Here, Sidders works with Dr. Naresh Thevathasan, who is the agroforestry research and development manager and an adjunct environmental biology professor. “This is the largest installation for this type of biomass research, with these types of management regimes, in Ontario,” remarks Thevathasan.

So far, the researchers have planted several sets of experimental blocks of different ages and types of production. "The plants all originate from vegetative cuttings,” explains Sidders. “We take one-year-old branches and stems, cut them into pieces, and that’s what we plant in the ground.” The cuttings are about 25 cm long and are planted vertically, with the buds facing upward and 20 to 23 cm of the cutting belowground.

Although the afforestation design is not harvested over the short term, the concentrated design is harvested regularly, with the first occurring after the first year of growth to stimulate the production of multiple stems. There-after, it’s harvested on a three-year rotation. “We cut the whole stems down to about 10 cm from the ground, and they regenerate from there.  That’s called coppice management,” says Sidders. “We’ll cut them and they’ll regrow from the stumps probably five to seven times before they lose their vitality.”

At GTI, the first blocks of concentrated and afforestation biomass were planted in 2005. Willow and poplar in the concentrated design were coppiced after one year of growth and now have up to 250,000 stems/ha, depending on the clone. In September 2009, these plants had three years of growth on four-year-old root systems. They will be coppiced for the second time in late fall of 2009, after the leaves drop and the trees enter dormancy. 

Newer blocks of all three designs were planted in late May and early June of 2009. By early September, some clones were already more than 1 m in height; these should grow another 40 cm before the first hard frost, likely in mid-October. The concentrated biomass will be coppiced in late fall at dormancy, using a sickle bar mower to cut the small, first-year stems.

“Our biggest challenge now is developing harvest technology that gives us the ability to be able to harvest chips, lengths, or bales, to make it easy for us to handle the plants,” says Sidders. The difficulty is in adapting harvest equipment so that it’s flexible enough to work with both willow and the thicker-stemmed poplar (in concentrated design), it can function in Canadian conditions such as light snow cover, and it’s suitable for localized agricultural areas, rather than huge industrial plantations as in Sweden that might better afford large six-figure equipment price tags.

Current harvesting equipment options include balers and modified combine-type systems. The combine-type system looks like a corn harvester, but cuts the material with a saw blade, chips it, and then shoots it into a following chip van. Because the chips are harvested green, they need to be either piled in a field to dry or processed in a dryer. The baler system cuts the biomass and wraps it into a cylinder, like a large hay bale. The bales can be left to dry in the field and then transported to a pellet plant or other facility and ground before use.

Thus far, it’s difficult to tell if the economics are quite there for this type of biomass production.  Currently, the CWFC estimates establishment costs at $8,000 to 12,000/ha for the concentrated design, which is about five to eight times the price of afforestation, says Sidders. The intensive site preparation and weed control in the first year of production are costly, requiring large initial investment. “We’re forecasting and validating the cost and productivity trajectories every year, based on the growth response. Our costs start high, but they are realistic. They’re pro-rated based on an operational scale, with full planting costs, all costs related to land, including land rental, and all the other liabilities all the way through the system, including equipment costs and supervision. If anyone says they are able to produce and recover the concentrated biomass for under $100/tonne, then you have to be skeptical.” 

The catch is that current chip prices are at least half that cost, and fossil energy prices are now low, although they likely won’t stay that way. Both the Globe and Mail and New York Times reported in August 2009 that natural gas prices reached a seven-year low that was actually below the cost of production. This type of situation makes it difficult for almost any type of bioenergy to compete with fossil energy.

However, the productivity of woody crops is still to be determined over the whole lifespan of an operation. For concentrated biomass, annual production is conservatively estimated by the CWFC study at 6 to 12 oven dried tonnes/ha thus far. Establishment costs are high, but productivity can increase over the first several harvests while management costs decrease. So those who plow the crop under before it reaches its full lifespan will not receive the full return on investment. In future, the crop’s value will also depend on the cost of carbon emissions and the value of carbon sequestration.

Still, Sidders does not expect woody crops to replace forestry residue biomass, but rather to act as a supplement. “It’ll only be economical in combination with other wood sources or other fibre sources,” he says. “If you’ve got a power plant up in the Hearst area, or Kirkland Lake, or Thunder Bay, for example, there’s cheaper access to wood fibre through the residues and waste material either at the forest or the mill.” But large energy users in agricultural areas have minimal access to forestry biomass without transporting it large distances. The economics may be such that an investment in woody cropping to supplement forestry biomass and reduce fossil fuel use makes sense. “If you’ve got a power plant going up somewhere, you grow it right beside it; you don’t grow it 100 km away,” says Sidders. “This is just an addition to the other sources of cellulosic biomass, including some agricultural crops.”

November 30, 1999  By Heather Hager


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