Farm Forestry New ZealandThe environmental benefits of forestry and wood use
Wink Sutton, New Zealand Tree Grower November 2006.
As all of us in the forestry sector know, maturing plantations are carbon sinks and remain as carbon reservoirs when harvesting begins, provided the plantation continues to be sustainably managed. Wood use is not only environmentally friendly but also very energy efficient. If the wood remains in a solid state, wood use increases the size of the carbon reservoir.
Because of its potential contribution for reducing control greenhouse gas, we might expect plantation investment to be encouraged and there would be a greater advocacy for an increased use of wood. Not so. The area of new plantings is now less than the area of plantations being converted to other land uses.
Wood versus steel and concrete
We have many apartments, stadiums, airports and commercial buildings being built of steel and concrete, with minimal amounts of wood. Both steel and concrete, or rather the cement content of concrete, require more energy for their manufacture than wood.
In addition to the energy required to manufacture both steel and cement the primary processes involved also add to atmospheric carbon dioxide.
Steel is made from iron that begins as iron oxide. On reduction, this produces iron and carbon dioxide. Cement is made in by heating clay and limestone together – limestone is a fossil carbon, calcium carbonate. In this process, which involves a kiln heated to 1500 °C, limestone is reduced to calcium oxide to form an aluminosilicate mixture. Carbon dioxide is a by-product and is released into the atmosphere. This carbon dioxide is not reabsorbed when cement is used in concrete – concrete is a mixture of calcium aluminate and calcium silicates.
The most important difference
Could the world reduce the release of fossil carbon dioxide by reducing the use of steel and concrete and increasing the use of wood? If we ignore that much less energy is required to process wood, a major question still remains.
Does wood, on burning or decay, become a greenhouse gas? By using more wood are we simply delaying the atmospheric release of carbon?
It is true that the carbon in wood eventually becomes atmospheric carbon dioxide and is identical to that from fossil fuels, metal oxides and limestone. However there is a very important difference. The carbon released from fossil fuels remains, for millions of years, a permanent addition to the atmosphere. Provided the wood comes from a sustainably managed forest an equivalent amount of carbon is removed from the atmosphere within a few years to grow more wood. The carbon from wood use should be treated differently from that of fossil fuels.
In other words, wood use recycles atmospheric carbon. The use of fossil fuel, together with the reduction of metal ores and the production of cement, permanently increases atmospheric carbon.
Advocacy for forestry and wood use would be more effective if wood use and plantation management was presented as a solution to the problem of increasing atmospheric carbon. Climate change spokesman for the NZFFA Denis Hocking notes that he has been pushing these arguments to the government, but the more pushing the better. New Zealand may have signed the Kyoto protocol to control greenhouse gasses but it is becoming obvious that the nation will be unlikely to hold greenhouse gas levels below those agreed for the first commitment period.
Wink Sutton is Patron of the NZFFA
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