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Growing Trees For Firewood

By Graham J Andrews

Published in Town and Country Farmer

Benjamin Franklin's prediction in the 1700s when he launched a new and more efficient wood heater, that ' ... our wood may grow as fast as we consume it, and our posterity may warm themselves at a moderate rate, without being obliged to fetch their fuel over the Atlantic' may have been a little too optimistic for present Australian conditions.

Firewood has become expensive, and is becoming scarce in some areas with the sources becoming further and further away from the major cities. In Canberra last winter firewood was selling for almost $100 a tonne; in Sydney and in Melbourne, for much more than that.

Wood fires, primarily as a source of heating, and sometimes as a source of cooking, have increased in popularity and usage in the past decade or so. This isn't really surprising, with the possibility of ever increasing oil prices in the years to come, when oil for heating could become exorbitant, and when even electricity could rise dramatically in price.

The development of new designs has led to efficient, clean and easy-to-use heaters. Wood as a cheaper source of energy has distinct advantages, but free firewood has even more attributes. Some firewood is collected from private land, or from clearing associated with other agricultural or forestry practices. Continual demand nevertheless may, in time, lead to a reduction or scarcity in supply from these sources.

Growing trees for firewood is therefore one option to overcome this scarcity of firewood in the years ahead. While growing a large number of trees for energy would not normally be feasible in an urban environment, there are nevertheless many thousands of farms and rural holdings where this can be easily achieved. Growing trees for commercial supplies has considerable merit just as it is more than feasible to grow them for your own small-scale domestic use. Trees are a renewable resource, and if they are properly managed, they can alleviate shortages of firewood, even if only as far as your own individual consumption is concerned.

While many farms have retained at least some trees, consideration has to be given to just how many more years these can be harvested. If the answer is an indefinite time, then it is unlikely that time will be spent planting trees solely for this purpose, but unfortunately many properties P-e devoid of trees - they are just endless plains of pasture or cereals with not a firewood tree to be seen - or harvested - anywhere. These are the properties that will benefit most from small plantations of firewood trees along with those desolate parts of most States.

Many huge areas were cleared of timber decades ago, leaving no real resources of firewood, and farmers or landholders throughout these areas should give serious consideration to not only establishing their own small scale plantings for domestic use but also the additional option of commercial-scale plantations.

The typical household in Australia uses between one and three tonnes of wood each year, but this amount of course depends on the climate, and whether or not a house is properly insulated; insulation alone can mean the difference each year of at least a tonne or more of firewood.

Yields of around 20 tonnes of wood (dried) per hectare per year are feasible with plantations. Trees used for firewood do not have to reach maturity before they are harvested, nor do their trunks have to be straight, or the diameters a minimum or even size. Trees with short holes, with knots, warps and splits are all useable because in fuel heaters it doesn't make any difference what they look like and whereas the need to split logs used to be a problem with some woods with difficult grains, smaller logs can be used just as successfully and may require no splitting; slow combustion heaters can take logs both large and small, small branches have their value too as kindling. All that is required is a good reliable chainsaw.

The trees can have several uses while they live - for honey production, or for fodder, or they may serve as windbreaks, or for roadway screening or a combination of these uses. Trees can be cultivated in small lots and can be planted and harvested on a short rotation - perhaps from five to ten years if they are properly managed and with domestic uses only in mind, smaller, fast-growing species are ideal.

They need not take up good agricultural land - that should be better used on a farm. Firewood trees can be grown on hills too steep for pastures, or they can be planted in areas that are too swampy for grazing. Trees for firewood can be planted initially as shelter belts, and in those out-of-the-way places on farms, the areas where tractors can't readily reach.

Since straight trunks and knot-free wood are not essential qualities for firewood, then we can look to other desirable characteristics. Ideally, trees fitting the requirements for firewood should:

• preferably have nitrogen-fixing ability, enabling them to grow satisfactorily in nitrogen-deficient soils. Acacias, being legumes, achieve this;
• show rapid growth. Again, many acacias, casuarinas and some fast growing eucalypts fit this category; and
• have the ability to coppice. Most eucalypts coppice readily if cut at the right time of the year.

The trees should have the ability to grow in degraded and deficient soils, as it is unlikely that farmers will devote their better land to firewood - a crop which, if used only for personal use, is not going to provide any financial returns. Legumes would be one answer. These trees (and in this family are included all the acacias, or wattles) provide their own nitrogen by means of nodulating rhizobium bacteria in their root system. Eventually, some of this nitrogen is made available to other plants in the vicinity. Wattles are hardy, resistant to many of the ills besetting other farm trees, and are fast growers. The wood burns cleanly and readily without much splatter and crackling.

Casuarinas too grow in impoverished soils, and are excellent for firewood. Although casuarinas are not legumes, they nevertheless use nitrogen-fixing bacteria, similar to those used by the legumes, and could be considered for planting in nitrogen-deficient soils.

The choice of species that coppice would provide fast growth with no re-planting after harvesting. Many eucalypts coppice time and time again without the need for replanting; the remaining stumps regenerate soon after cutting, from dormant buds. The new shoots grow vigorously because they are served by roots that fed the former much larger tree. Cutting young trees generally results in a number of new stems from the remaining stump.

Eucalypts will coppice many times before they have to be removed and replaced. The first crop can be harvested (depending on the species, climate and other factors affecting tree growth) within about seven or eight years; subsequent cuttings from coppiced growth, on five to six-year rotations.

Eucalypts can, depending on the particular species, as well as climatic conditions, reach six or seven metres in only six years, and contribute 20 to 25 tonnes of firewood per hectare each year.

Several diseases and pests are known to reduce the growth of eucalypts. To help prevent insect attack, there might be considerable merit in not planting monocultures of eucalypts, but in planting acacias first. Maybe the added advantage here is that the acacias will ultimately provide nitrogen to the soil and subsequently to the eucalypts. And being fast growers, they will provide an early crop of firewood until the eucalypts are large enough to become firewood. The acacias will also attract birds which will lessen insect predation on the young eucalypts. They'll even provide protection from strong winds.

Establishing the Trees

Seeds are cheap - a kilogram of eucalypt seeds may cost a couple of hundred dollars if bought, but that's enough for a million trees or more - more than will be needed for personal firewood needs! Thirty to fifty grams of seeds should be sufficient. Acacia seeds are much larger, with fewer per kilogram, but are much, much cheaper. The seeds can be planted directly into the prepared ground after necessary preparation to ensure germination, or young tree seedlings can be raised in nurseries and planted out later on. Plantings at the rate of about 2500 trees per hectare - about two by two metres - will provide a healthy sized plantation. Certainly establishing the young trees direct from seed rather than using established trees from a nursery has much merit, even accounting for some loss, merely be cause of the saving. Seeds can be purchased from native-seed suppliers, or from forestry offices, or can be collected locally.

The young trees will need protection from domestic animals and from wildlife that will find the shoots attractive. The trees will also need to be protected from fires, and here proper safeguards, such as reducing competition from long grass and establishing firebreaks around the perimeter of the plantation, will pay off. Eucalypts are not generally destroyed permanently by fire, but it would be ironic to have a firewood crop destroyed by the very purpose for which they are grown. Even if the tops of eucalypts are destroyed by heat, or if the trunks are burned, regrowth can occur shortly afterwards, either from the trunk, or from the lignotuber. Although trees such as eucalypts will regenerate in time, several years' supply of firewood can be lost prematurely in a bushfire.

So what species are suitable for planting for firewood? Often with this type of crop, it may at some time be a matter of 'what you can get', rather than 'what you really want' but consideration must be given at all times to ensuring that the trees suit the specific climatic conditions, soil type etc. Although woods like red box and yellow box are readily sought after, other species are often preferable for growing for a number of reasons, such as their fast growth rates, wide tolerance of rainfall, ability to withstand drought, and adaptation to a variety of soil types.

Eucalypts, casuarinas and acacias all have woods that are compact and heavy, and can be made to burn at a steady rate. Of the eucalypts, those that should be placed near the top of the list would include Eucalyptus globulus, E. grandis (although this species is affected by fire, and does not have the usual lignotuber from which it may regenerate), E. fastigata, E. carnaldulensis, E. saligna, E. obliqua, E. nitens, and perhaps E. muelleriana. These species are all fast growing trees, with high yields; all need reasonable rainfall.

Casuarinas are suitable, and give excellent firewood, just as do most of the larger wattles. Of the acacias, some of those that are suitable include A. melanoxylon, A. acurninata, A. dealbata, A. decurrens, A. elats and A. mearnsii. And of the casuarinas, the Casuarina cristata and C. cunninghamiana will fulfill their role admirably.