Energy forestry
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Energy forestry is a form of forestry in which a fast-growing species of tree or woody shrub is grown specifically to provide bio-fuel for heating.
The advantages to using grown fuels as against fossils fuels such as coal, natural gas and oil is that while they are growing they absorb the equivalent in carbon dioxide, an important greenhouse gas that will later be released in their burning, whereas by burning fossil fuels we are increasing atmospheric carbon by burning carbon that was added to the carbon sink in a time when the Earth would have had a very different climate, and this is a prime cause of global warming.
The main way in which energy forestry is carried out is by dedicating areas to the cultivation of appropriate species, and typically the species chose is the Common Osier or Basket willow, Salix viminalis. This species is selected for its broad acceptance of climate and soil conditions, relative insusceptibility (from year two onwards) to pests and diseases, ease of propagation and speed of vegetative growth.
Willow's high production is maintained by short rotation periods, about three to five years. After each harvest the established root system and the nutrients stored in the roots and stumps guarantee vigorous growth for the shoots.
Willow plantation is established with stem cuttings about 20 cm long, which should be soaked in water for about two days before planting just like any other tree plants. During the establishment year the plantation is susceptible to drought and weeds, and that is why irrigation and efficient weed control must be taken care of.
Planting density is about 18.000 cuttings per hectare. Planting starts immediately after preparing the land and taking care of weed control. The high moisture of the soil in the spring and the amount of sunshine in the early summer will stimulate root penetration and shoot development.
The most efficient planting machines plant four rows at a time. It takes about an hour to plant a hectare.
Production during the establishment year is low, usually less than 1000 kg per hectare. After the first summer the shoots are cut and the actual production period starts after the establishment year.
When the plantation is properly established, it is possible to gain annual yield of about 9.000-12.000 kg dry matter per hectare. This is equivalent to the energy content of 3,7-4,9 tons of heating oil. It is possible to repeat harvesting a plantation without re-establishing it for about 25-35 years.
During the establishment year the dry matter production is low. The first few years after the establishment are part of the establishment phase. During subsequent rotations annual yield will be better than at the start. As a pioneer species, the yield of the willow may decrease after the third growing rotation.
Willow plantation is harvested in winter after leaf fall, when the soil is frozen. When the shoots are harvested as whole stems they are easy to storage. Scheduling subsequent operations is also more flexible. The stems can be dried for combustion in a pile outdoors; the moisture content of the wood will decrease to about 30 % on average until the next autumn.
The most efficient harvesters are heavy self-powered machines, which cut and chip the shoots on a loading platform. Direct chipping reduces costs considerably, since a separate chipping in the store will be excluded. Some chipping harvesters can be attached to an existing tractor. It takes about 3 hours to harvest a hectare with it.
Energy forest that is ready for harvesting has about 40.000 - 50.000 kg dry matter per hectare. The shoots are 5-6 meters high and have a diameter of about 3-5 cm at breast height. That amount of dry matter equals to about 110-135 cubic meters solid volume.
The price of dry willow as a heating fuel is currently around 45 Euro per tonne in most of Europe.
This is not a relatively high-return crop, but it is low-maintenance, is a way of utilising difficult fields, and can be combined with the production of material for wicker work, and is and environmentally friendly type of farming as little or nothing in the way of pesticides and treatments are usually necessary.
Grants may also be available in some jurisdictions to further this type of land-use.
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