Energy independent farming (Part one): Wood Biomass Energy

In this series of articles we explore options to produce on-farm green energy in the form of fuel, heat and electricity to reduce one of the largest costs of a farm business as well as to work towards ending farm dependence on fossil fuels

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Tree planting, Northumberland County, 1930
(Image: http://www.northumberlandcounty.ca/)

Before the green revolution extended into Ontario and traditional rotations were supplanted with more intensive cash crops, most farms here in eastern Ontario kept woodlots. Once the harvest season was over and the frost rolled in, woodlots provided off-season work for farmers, a source of firewood for heating, lumber for building, and even as a cashcrop for sale to sawmills or papermills during the boom years of the Canadian lumber trade.

While many such woodlots were merely selectively cut native forest, as early as the 1910s the government of Ontario began subsidizing and encouraging the establishment of tree plantations on farmland to prevent erosion and desertification. Such tree plantations could be established on land otherwise unsuitable for farming, and provided higher yield and higher quality lumber than unmanaged woodlots and were often used in multigenerational rotation with pastures after clearcutting. This system had very significant benefits - both economically as on off-season supply of income and ecologically in preventing dessication of both farmland and riparian land, as noted by an Ontario Department of Agriculture report on reforestation in 1908:

"The policy of putting these lands under forest management has many arguments in its favour. It will pay as a financial investment; assist in insuring a wood supply; protect the headwaters of streams; provide breeding ground for wild game, provide object lessons in forestry, and prevent citizens from developing under conditions which can end only in failure."

However, times have changed. Farmers no longer primarily rely on wood for heat given the affordability and availability of fossil fuel heating, they no longer fell trees for their own building lumber given the quality and availability of bought lumber and the increasing popularity of non-wood structures on farms, and the lumber trade has slowly died, with prices being too low to interest most farmers. Tree plantations, which take 2-3 decades before any return can be realized, are now mostly the domain of dedicated logging businesses or are established as permanent windbreaks with no direct value returned to farmers.

A 140MW generating station in Vaasa, Finland powered by
a mix of forestry waste and dedicated energy wood produced
by farmers (Image: http://www.power-technology.com/)

The same is not true elsewhere in the world. In northern Europe and the British isles, tree plantations are making a comeback in an unexpected form - energy wood. With increasing interest in renewable fuels many former fossil fuel generating stations are being converted to "biomass" generating stations which are fuelled by wood chips.

In Europe, however, farmland is a precious and limited resource. Turning over farmland to a crop which will only yield once every 20-30 years is infeasible given the price received by farmers for chipped wood fuel. European farmers have instead had to refine woodlot management techniques that produce significant amounts of woody biomass on a short rotation. These techniques, now known as Short Rotation Forestry (SRF) and Short Rotation Coppice (SRC), mainly supply large generating facilities in Europe. Eslewhere in the world, the mixing of tree plantations of cropland, known as Agroforestry is a popular system for the production of energy wood. Here in Canada though these techniques are mainly of interest for the on-farm generation of heat and/or electricity, especially here in Ontario given the economically lucrative Feed in Tariff system.

Short Rotation Forestry

7 year old hybrid white willow
(Image: http://silvanusforestry.com/)

While traditional tree plantations take up to 30 years to yield a harvestable amount of lumber, in recent years there has been developments of hybridized fast-growing tree species that can reach maturity in as little as 5-10 years. While such trees don't yield useful lumber for sale to sawmills, they can produce high yield woody biomass on a short rotation enough rotation to be a profitable farm crop for farmers. While the most popular species for this system are hybrid birch and hybrid poplar, which are harvested at 8-12 years of age, shorter growth hybrid willow can also be used for round wood production, harvestable in as little as 5 years. Such plantations can also yield valuable crops for farmers; white willow bark is a valuable natural pain relief tea which retails for up to $8.80/lb, birch can yield birch syrup which retails for up to $250/L, and poplar remains the most common tree for sale to the pulp and paper industry.

Short Rotation Coppice

Coppice sprouting from a willow stool
(Image: http://www.willowbasketmaker.com/)

"Coppicing" refers to a traditional English woodlot management technique used on some types of fast-growing trees of felling a tree, and then leaving its stump in the ground to sprout new smaller trunks which can then be later harvested during winter up to 10 times before the stump must be removed and the tree replanted. Traditionally SRC was used to harvest willow and hazel for basket-weaving, with dozens of farms in the UK still producing traditional coppice products today. However since coppice can be harvested once every 2-4 years, allowing for an incredibly short rotation without replanting after every cutting, SRC has also become the dominate form of wood energy production in the British Isles and the Nordic countries. The most common tree used for this purpose is hybrid willow planted in double rows, though hazel and hybrid poplar are also used planted in single rows.

While the woody biomass produced in SRC far outyields SRF to the acre, harvest is a challenge. Harvest of coppice is a tedious task that can only be done in the short period between complete leaf loss (and thus beginning of dormancy) for the tree and the first major snowfall, typically November to early December. While small plantations can get away with hand harvest, larger plantations use a variety of different mechanized harvest systems:

New Holland forage harvester with 130FB
coppice header (Image: www.wnif.co.uk)

Chip harvesting: The most widely used system, this one-pass harvest has the highest productivity and is preferable for the largest plantations. Essentially a modified forage harvester is used to cut the coppice into wood chips while harvesting, both smaller pull-type models and headers for self-propelled forage harvesters are available. While the most productive in the field, this method has a drawback. The wood chips have above 50% moisture content at harvest, and if left to store in open heaps will ferment and develop bacteria which can lead to losses of over 28% of the fuel value of the wood. In order to maintain the value of the chips long-term it is essential to build indoor storage facilities, preferably ventilated, and even then the chip will lose heating value moreso than other harvest methods stored outdoors. Additionally the chip system is more useful in shorter rotations (2-3 years) than longer ones, as larger coppice will lead to more frequent jamming of the harvester.

Salixab coppice billet harvester
(Image: http://agroenergie.ca/)

Billet harvesting: Using a modified sugarcane harvester, these self-propelled systems cut the coppice into 20cm or 10cm long logs. These "billets" store much better than wood chip, with fuel value losses of as low as 3% after a year's outdoor drying. However the billet harvest system is an expensive investment compared to other harvesting machines, and harvests less acres/hour than chip harvesters. Another drawback is the need for a second harvesting step: once the billets are dried and ready to be used, they have to be chipped using a stationary wood chipper. Additionally the system still loses some fuel value to fermentation compared to whole stem harvesting.

Anderson BioBaler
(Image: http://www.landwirt.com/)

Whole stem harvesting: These harvesters simply cut the coppice at the base and bundle the whole stem for later processing. While their productivity per acre is much lower than the other two systems, whole stem bundles have zero loss in fuel value even when stored outdoors in uncovered heaps for periods of over a year. As with the billet system, the bundles must be chipped before use. While not as productive for larger plantations this system is recommended for smaller plantations due to the ease of storage. There are three different styles of machine for whole stem harvesting; the first is the BioBaler, manufactured in Québec, which relies on using a 200hp+ tractor mounted with a ram to knock down the coppice and feed it into the trailed baler which produces round bales of coppice stems.

NB Stemster Mk III Harvester
(Image: http://www.nordicbiomass.dk/)

The second is a trailed harvester which can be hauled by a 75hp tractor manufactured in Denmark that cuts the coppice and lays it into a trailer, this trailer can then eject the pile of willow once full. Though the BioBaler system is the more productive of the two, the high-power tractor requirement may be a barrier to most interested producers, and the equipment to shred the biobales will need to be larger (and more costly) than a smaller wood chipper sufficient for the Danish system. The Danish system is also preferable for those doing longer rotations (3+ years) as it can handle thicker coppice than other
harvesters. Another similar piece of equipment is Weremczuk Aronia Cutter

Weremczuk Aronia Cutter
(Image: http://aroniaharvest.com/)

manufactured in Poland for an 80hp tractor. This machine is designed for the clearcutting of aronia berry plantation, which coppice readily and need to be re-cut every several years to continue producing. Unlike the Danish harvester which collects the coppice into a trailer, the aronia cutter knocks it into strait lines beside the rows. From there it has to be collected using a front loader or by hand. The aronia cutter may be more suitable to those who intend to do wide row spacing for co-use as pasture or for those who intend to store their coppice in the field and use it as needed, the heaps of whole stems will store outdoors with no loss in fuel value.

Naava Grip 1500 25-E Feller-Buncher
(Image: http://www.canadianbiomassmagazine.ca/)

The third is an energy header feller-buncher, attached to either tractor-mounted forestry arms or dedicated log wagons, are designed to grab, cut, and move coppice as whole stems. This is the least productive harvest system in terms of acres/hour, but it is also the cheapest, with a tractor mounted feller-buncher coming in at around $9,000, and with other headers these machines can be useful for other farm tasks as well. Also, like the Danish trailed harvester, these felling heads can accomodate thicker coppice from longer rotations.

Agroforestry

Ginseng among a tree plantation in Maryland
(Image: http://www.hardingsginsengfarm.com/)

Both SRF and SRC systems can be integrated with field crop production for mixed-use farming known as "agroforestry" instead of dedicating land to biomass production alone. Tree plantation strips within a field provide natural windbreaks that generate economic value while preventing erosion, particularly important for those of us with erosion prone sandy or muck soils. Tree plantations also provide shade to crops which require it, which would otherwise require costly artificial netting. Agroforestry may be of particular interest to ginseng producers due to the shade produced and the fact that ginseng is produced on a similar rotation length to SRC and SRF.

Another use for coppice plantations is as pasture for sheep. In England, traditional coppice plantations for basketry are usually stocked with sheep to "clean" the plantation of any grassy overgrowth before harvest. And the coppice is of benefit to the pasture too - in poorly drained or compacted clay and muck soils the deep tree roots can help improve the productivity of pasture. As well, nitrogen fixation by the pasture and manure from the sheep acts as a natural fertilizer to a plantation. Establishing an enclosed wide-row coppice plantation stocked with sheep can help add value to otherwise low-productivity land.

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While tree plantations are a major source of on-farm bioenergy, they are not the only one. In later articles we will explore agricultural byproducts for energy use as well as dedicated energy crops, and how to turn all of it into environmentally-friendly cost-savings and even cash profit for your farm.