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Firewood

        

Firewood is a renewable resource that was, until the onset of coal mining in the 19th century, the primary source of fuel in Britain.  In many countries of the developing world, and in the more remote, colder parts of Europe, North America, Asia and Australasia, firewood remains an essential source of energy for heating and cooking.  In Sweden, the burning of wood in power stations is used to produce a significant amount of the nation's electricity, though much of their firewood is imported from Baltic countries where labour is less expensive.

Although the use of firewood was restricted to rural areas of Britain throughout the 20th century, in recent years, firewood has been making something of a comeback.  Typically, this is because of economic factors, since recent large increases in the price of natural gas and oil have made the felling, processing and transporting of firewood more economically viable.  Previously, the market for firewood was restricted and suppliers struggled to make a profit after taking the labour and machinery costs into account.

 The future reliance on firewood is likely to increase for a number of reasons:

  • The resource is renewable provided the consumption rate is controlled to sustainable levels.
  • Fossil fuels (natural gas, oil and coal) are non-renewable and will become more expensive as the rate of production declines, unless other sources of fuel adequately replace them.
  • The increasing use of woodburning stoves and improvements in their safety and efficiency.  It is not against the law to burn firewood in smokeless zones provided well seasoned timber is burnt in an efficient stove since this produces negligible amounts of smoke.
  • The environmental benefits - the growth and burning (or decay) of the same mass of wood is carbon neutral.  This is not true when the felling, processing and transport of firewood is factored in, but when compared to the intensive production of agricultural crops for biofuels, the carbon dioxide emissions are very small.
  • The protection and sustainable use of ecosystems and the natural resources we acquire from them will become increasingly important to us.  The appropriate management of woodlands has additional benefits to wildlife conservation and helps to lessen the impact of storms and flooding events, which are expected to become more frequent and severe as a result of climate change.
  • Government grants that encourage efforts to protect the natural environment, including ones targeted towards the sustainable production and use of biomass, are likely to increase.
  • The market for softwood timber planted in upland areas of Britain throughout the second half of the 20th century was severely limited following the decision to produce all our paper from almost 100% recycled material.  An alternative market for the thinnings from these conifer plantations is likely to be biomass production.

A number of general points about using firewood for heating (and cooking) should be noted:

  • Always burn well seasoned firewood (ideally air-dried for at least 12 months).  The burning of freshly felled ('green') timber produces less heat, more smoke and tar deposits in the chimney.
  • Ideally burn hardwood timber since it is typically more dense than softwood timber.  More heat is therefore released from a given volume of hardwood timber when compared to the same volume of softwood timber.
  • Always compare the price of firewood by volume and not by mass.  If you buy a tonne (1000kg) of green timber, you will have bought anything from 250kg to 650kg of water!  However, if bought by volume the price should reflect the density of the wood, e.g. the density of dry oak timber is ~750kg per cubic metre compared to most coniferous species, poplars and willows, which range from ~350kg to 600kg per cubic metre.
  • The burning properties of each species are also important (see table below).  The best species is probably ash because of its low moisture content, but there are many native trees and shrubs that make good to excellent firewood.  There are also several non-native species such as sycamore and rhododendron that can be utilised as firewood when they are removed from native woodlands in order to improve their ecological value.
  • Always burn firewood in a woodburning stove or wood cooker.  The modern stoves are more than 70% efficient, compared to only 30% efficiency with an open fire.  The size of the log is also important since wood is a poor conductor of heat.  A log diameter greater than 10cm or 4in reduces the efficiency, particularly in smaller stoves.  Larger pieces of firewood require splitting, the ease of which depends on the species and dimensions of the log.

At current prices, the price (per unit of energy) of firewood is cheaper than natural gas or heating oil.  In order to keep the cost as low as possible, firewood should be bought from a local supplier, since transport costs represent a significant proportion of the total.  Alternatively, access to your own firewood resource can help to reduce the cost of heating your home to a low level.

Although it is not practical for everyone to utilise firewood for heating, an increasing number of small woodlands are owned by individuals.  The reasons for private ownership include for tax purposes, conservation and recreation.  The production of timber products is often not even considered, but with a limited amount of training and machinery, producing firewood for personal use at least is entirely possible.

A number of general points about producing firewood from your own woodland should be noted:

  • The production of firewood is best carried out using the coppice system (or coppice with standards) - a felling licence is not required to cut coppice poles with a diameter at breast height (1.3m from the ground) of 15cm or less.
  • A well stocked mixed broadleaved coppice woodland should produce approximately 3 tonnes of air-dried wood per hectare per year.
  • An average three bedroomed house would need 7-9 tonnes of air-dried wood to provide all the heating requirements.  The area of coppice woodland would need to be at least 3 hectares in order to be self-sufficient in firewood.
  • The most efficient way to manage coppice woodland is to cut all coppice stools in a particular area (known as a coupe).  This ensures that all the stools have a sufficient amount of sunlight in order to grow back rapidly after being cut.
  • The 3 hectares of coppice woodland ideally should be divided into 10 coupes of 0.3 hectares.  If one coupe is felled in turn each year, i.e. on a 10 year rotation, each coupe will produce approximately 9 tonnes of air-dried wood over those 10 years (enough for one year's heating requirements).
  • The 10 year rotation should ideally produce coppice poles that are approximately 6m in length and 70-100mm in diameter in order to maximise the handling and burning efficiency.  The regrowth of the poles obviously depends on the species, the local climate conditions and whether it is matched to the underlying soil type.
  • If a smaller area of coppice is available, the yield per unit area can be increased through the use of faster-growing species such as alder, poplars and willows (provided climate and soil conditions are suitable).  Producing firewood from an area less than 1 hectare becomes more difficult because shading from surrounding or edge trees is greater with smaller areas.  Larger coupes have a larger area to edge ratio than smaller coupes (especially if the shape is roughly square) - this reduces the cost per unit area when fencing against deer or rabbit browsing.
  • The coppice should be cut in the dormant season from late autumn to late winter.  This ensures there is the least quantity of water within the coppice poles, which reduces the time taken to season the firewood to a minimum.  Cutting in the dormant season also appears to result in better survival of stools, quicker initial regrowth of shoots and a greater number of new shoots.
  • It is not necessary to store firewood under cover but it does reduce the time taken to season the wood if it is stored in an open-sided shed or barn.  The coppice poles can be stacked to dry in the woodland if there is no risk of theft.  Ideally, 10% of the cut timber should be left as deadwood piles, but this can include all the smaller side branches and tops - these can be stacked around the cut stools in order to provide protection against mammal browsing.

The burning properties of each species should be considered when planting a new coppice or restoring a neglected area of woodland back to well managed coppice.  The following table lists the native species that are suitable for firewood production - the best firewood is produced from the species at the top end of the table.  A few non-native species that can be used as firewood are listed at the bottom of the table.

Species

Burning Speed

Comments

 Ash

Good

 Low moisture content when green - little seasoning needed

Beech

Good

Season for a year; excellent deadwood species

Hornbeam

Good

Season for a year; more common in southern Britain

Hawthorn

Good

Season for a year; thorns make handling more difficult

Crab apple

Good

Gives off pleasant smell - useful for cooking

Oak

Good

Season for a year; excellent for keeping fire lit overnight

Field maple

Good

Season for a year; grows better on more fertile soils

Elm

Good

Season for a year but often found dead and ready to burn

Hazel

Good

Good coppice species; important for wildlife conservation

Birch

Fast

Burn with slow burners such as wild cherry

Wild cherry

Slow

Burn with fast burners such as birch; pleasant smell

Blackthorn

Slow

Season for a year; burn with fast burners such as birch

Rowan

Slow

Burn with fast burners such as birch; attractive berries 

Holly

Slow

Burn with fast burners such as birch and alder

Yew

Slow

Very dense timber and slow growing

Alder

Fast

Burn with slow burners such as wild cherry

Poplars

Fast

High moisture content - season for a year

 Willows

Fast

High moisture content - season for a year

Lime

Slow

Good coppice species; burn with fast burners such as birch

Rhododendron

Good

Very invasive non-native species on acidic soils - eradicate

Sycamore

Fast

Invasive in ancient woodlands - eradicate

Sweet chestnut

Fast

Not invasive but gradually remove and replace with hazel

Conifers

Fast

Season for a year - pine, spruce, cypress burn
quickly; Douglas fir, larch burn slower

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Derbyshire, DE73 7JZ
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