Willow Rings, Poplars Offer A Clean Energy Alternative

“This biobaler will handle stems up to six inches in diameter, so it will actually take down fairly nice-size aspen as well.”

– BILL SCHROEDER

Good King Wenceslas may have called for his servant to “bring me pine logs hither” to fend off the winter’s chill, but for common folk in the Middle Ages, the fuel of choice was more likely bundles of coppice wood.

Coppicing, or the practice of cutting off trees close to the ground then harvesting the new growth in rotations lasting anywhere from seven to 20 years, had the advantage of easier harvesting than sawing up and splitting logs from mature trees.

Cut from broad-leafed tree and brush species, coppice wood was one of the few “forever” renewable fuel sources developed by mankind with the added benefit of providing varying levels of cover for wildlife. But the ancient European practice fell out of favour in the decades after the Second World War due to the availability of cheap fossil fuels and the decline of folk crafts.

The modern version of coppice wood harvesting could operate in a similar fashion, right here in Manitoba, according to Bill Schroeder, a research manager specializing in agroforestry at AAFC Indian Head.

But instead of slicing off the willow, ash or poplar shoots with a sharp knife and tying them into small bundles like medieval villagers, farmers on the Prairies could convert brush and shrubs heretofore thought of as a nuisance into valuable heating fuel with a heavy-duty brush baler, and at the same time improve wildlife habitat by encouraging lush regrowth for everything from ducks to deer.

That would increase the value of the “willow rings” that surround Prairie potholes and wetlands, and give farmers a reason to not drain, bulldoze or disc them out of the landscape, he said.

“Why are we losing a lot of our wet lands ?” asked Schroeder, in a presentation at the Manitoba Conservation Districts Association annual convention held recently in Brandon.

“I think one of the reasons is that the benefits to a landowner of retaining them are

not really apparent. In many cases, the landowner sees the wetlands benefiting the general public, but not really himself.”

Up until about a century ago, willow rings around potholes were controlled naturally by grazing herds of bison or by Prairie fires. By comparing old and new aerial photos, it is apparent that willow rings are increasing, and there are now more than there were 100 years ago, he said.

However, much of the growth is decadent, meaning that 40 per cent of it is old, dead wood that needs to be cleared out so that new growth can flourish.

A project recently undertaken near Elkhorn, Man., tried

out the WB-55 biobaler developed by the Anderson Group in Quebec.

The 13,000-pound machine pulled by a heavily armoured, 180-hp tractor with logging tires, shreds the willows with hydraulic-powered rotating knives moving at 2,000 r. p. m. s, and then spits them out in neat 1.2X1.5-m, 500-kg bales at a rate of 6.8 tonnes per hour.

Out of 1.83 hectares of willow rings harvested, yield was 143 bales, each weighing about 340 kg, with a moisture content of 28 per cent. Out of three willow rings of varying sizes, nearly 50 tonnes of biomass were harvested in total.

The machine sells for $125,000, plus the cost of armour plating to protect the tractor’s underbelly.

“This biobaler will handle stems up to six inches in diameter, so it will actually take down fairly nice-size aspen as well,” said Schroeder, adding that it could be used to roll up other pasture-encroaching species such as wolf willows, snowberry or caragana shrubs gone wild.

If the bales are allowed to dry to 20 per cent moisture and then burned in a high-efficiency European-designed boiler, three bales – or roughly one tonne of biomass – have a BTU value equal to 400 litres of heating fuel.

Leftover ash, which as a side benefit contains valuable fertilizer nutrients, was only 1.65 per cent, he added.

The violent shredding action of the biobaler did not seem to hinder regrowth. The following spring, the willows were seen to have bounced back quickly.

One problem that Schroeder foresaw – common to all bulky, biomass energy sources – is the relatively low energy density of the bales which makes them only practical for use as a local resource.

For that reason, the bales would need to be used no farther than 30 kilometres from the source, or else the diesel fuel expended in baling up the willows and trucking them away would exceed their value as heating fuel.

Likewise with pelletizing. Because the process is so energy intensive, it tips the input-output balance into negative territory.

“For a landowner with a shop and a house, a hectare of willow rings would be enough to meet his heating requirements for two years,” said Schroeder. [email protected]

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