Trees make food for their growth by photosynthesis.  Leaves absorb carbon and oxygen in the form of carbon dioxide.  Inside the chloroplast in the cells, the chlorophyll molecules (the plant’s green pigment) use energy from the sun to make the hydrogen from water combine with the carbon and oxygen to form soluble carbohydrate – sugars.  The sugars can then be made into starch for storage.  Much of this starch is converted into cellulose – the building material for the cells which make up the wood.  Cellulose molecules are made up of long chains of carbon and hydrogen atoms and this is why wood is full of carbon.  For as long as that wood is intact, whether as growing trees, timber in buildings and furniture, fibres in paper and books, etc., then that carbon remains locked away in the structure of the wood.

Trees need energy to grow.  This energy is released from the food made by photosynthesis in a process of respiration.  Some of the food is combined with oxygen and the reaction releases stored energy for growth.  Respiration uses between a quarter and a half of the food produced in photosynthesis.  Respiration uses oxygen and releases energy, carbon dioxide and water.  This is the reverse of the photosynthesis which collects the sun’s energy, combines it with carbon dioxide and water and releases oxygen.

The combined effect of photosynthesis and respiration is that trees absorb more carbon dioxide from the atmosphere than they release.

Trees store or 'lock up' carbon by their natural processes 

Thus, carbon is effectively ‘locked up’ or ‘sequestered’ by growing trees and will only return to the atmosphere when the tree dies, decays or is cut down and burnt.  Products made from wood retain much of the ‘locked up’ carbon within their structure.

It is calculated that the forests of the world hold a carbon stock of over 1,200 billion tonnes, almost double the amount of carbon present as carbon dioxide in the atmosphere.

For more information about carbon sequestration, see ‘How Trees Function’ in the Forest Habitat section of this site.

Continuing deforestation, occurring now mainly in tropical regions, is responsible for annual emissions of between 1.1 and 1.7 billion tonnes of carbon.  It is estimated that one hectare of tropical forest is felled every second – falling victim to either illegal logging operations or ‘slash and burn’ clearance for agricultural use.  In the tropics, the soil that has developed beneath a forest canopy is fertile for only a short period before nutrients leach out – farmers then abandon the land and cut down more forest.

During recent years a succession of initiatives involving the United Nations, national governments and international trading blocs have tried to curtail tropical deforestation – with little success.

Plantation forests lock up 0.2 billion tonnes of carbon every year

However, in other regions, plantation forests are a significant carbon sink with an annual sequestration rate of around 0.2 billion tonnes.  While this is encouraging, a lot more forest needs to be planted to compensate for massive deforestation in the tropical regions.

Commercial planting rates vary according to economic factors – international market demand for wood and fluctuating rates of return – but it is hoped that the possibility of trading forest generated carbon sinks under the terms of the Kyoto Protocol will be a major incentive for extensive new planting in many countries.

The overall effectiveness of plantation forests as carbon sinks is also put at risk by wild fires and, ironically, the effects of global warming are already dramatically increasing this risk in many temperate regions where long, hot summers and prolonged droughts are increasingly common.

In Canada, which has about 10% of the world’s forests, the area burned in the 1980s-1990s doubled from the 1970s according to the Canadian Forest Service.  Forest fires now release about 150 million tonnes of carbon dioxide each year in Canada, set against the total, in 2002, of 730 million tonnes resulting from other activities.

How Wood Can Balance The Carbon Budget One of the most effective ways to reduce emissions of greenhouse gases is to use wood instead of other materials for building and landscaping, furniture, finishing, etc.  Every single time a cubic metre of wood is used instead of a cubic metre of other construction materials such as concrete, blocks or bricks there is an average saving of 0.8 tonnes of carbon dioxide emissions. A study by Australia’s Co-operative Research Centre for Greenhouse Gas Accounting found that about 2.7 tonnes of carbon dioxide was released in the manufacture of steel framing for a typical four-bedroom, single-storey home.  This included the carbon dioxide released from mining the iron ore and turning it into steel as well as the effects of transportation of product.  By comparison, a timber framed house released just 0.4 tonnes of carbon dioxide, in large part due to the significant amounts of the gas taken up by the growing trees.

Environmental Impacts of Products Life Cycle Assessment (LCA) is a methodology for the objective assessment of the environmental impacts arising from the production, use and disposal of different products and services.  LCA takes into account such impacts as global warming, ozone depletion, resource depletion, eco-toxicity and nutrient enrichment.  LCAs indicate that wood products typically have less environmental impact compared to competing non-wood products such as steel, concrete, aluminium, PVC, etc. in terms of energy used and global warming potential.  The LCA of wood products takes into account the growing of trees (including propagation, site preparation, planting, silviculture, tending and harvesting); processing of wood into products; using products; life of the end use application (i.e. durability of buildings); and withdrawal of the product from useful service (disposal, re-use, recycling). Timber frame house construction

Comparison with other materials The production of a cubic metre of aluminium requires more than 300 times the amount of energy required for the production of a cubic metre of treated wood. Structural steel requires around 375 times the amount of energy. The difference in the amount of carbon emitted during manufacture of these materials is dramatic.  Material Carbon Emitted Aluminium 6325 kg per m3 Steel 8117 kg per m3 Wood -228 kg per m3 Wood shows a negative figure is because allowance has been made for the amount of carbon that remains 'locked up' in the structure of the wood throughout its use as a timber product.   Concrete slab & steel construction

Versatility And Performance Benefits Of Wood Wood is the only material resource that is totally sustainable and renewable - processing of timber and the manufacture of wood products require comparatively little energy and so result in fewer greenhouse gas emissions. But, in addition to these environmental credentials, timber products offer many advantages – Strong in relation to weight Excellent thermal insulation properties Good acoustic absorption and insulation Innate flexibility – high tolerance of thermal stress, earthquake movement, strong winds, etc. Easy to process, handle and install Aesthetically pleasing The supreme versatility of wood has been further extended by the development of advanced timber treatments and finishes which enhance natural durability and make it suitable for the most demanding of applications giving resistance to:  Fungal decay and rot Insect attack Absorption of water Fire This combination of characteristics is unique – wood is a high performance material capable of meeting a broad range of building and manufacturing needs.  And, most exciting of all, its full potential has yet to be explored – for instance, biotechnologists are discovering that wood can be used to manufacture products that were previously derived from petro-carbons (plastics) and to produce fuel that is a ‘clean’ and sustainable replacement for oil and coal.