Letter: Forests aren't sinks

From Paul Back

Rigel Jenman in his article on the valuing of trees seeks to perpetuate the idea that the forest has a “capacity to maintain a stable atmosphere by fixing carbon dioxide and producing oxygen” (Letters, 29 July). We are taught this truism in school. Unfortunately it is taken by many as a reason for protecting virgin old-growth forests, including tropical rainforests, because people believe these forests have the ability to suck up great amounts of carbon dioxide while only giving back oxygen.

This, however, is not the case. Any climax (undisturbed and in balance) plant community is “carbon neutral” – that is, it puts back into the atmosphere as much carbon as it takes in through transpiration. The carbon is released when the plants die and are broken down on or in the soil. Both carbon dioxide and methane are released into the atmosphere. All of a plant community’s production – leaf fall, flowers, fruit and dead plants – are handled in this way.

The only time a plant community can be “carbon positive” is when it is dynamic, and a community is only dynamic following disturbance. This disturbance can be caused by nature, in the form of fire, flood, drought or storm, or by humans. When a forest is recovering from disturbance it is fixing carbon at a great rate.

It follows that the best way to use forests to remove carbon from the atmosphere is to harvest timber. Provided this timber is used for long-term products such as houses and quality furniture, then this carbon is tied up for many decades, maybe centuries. Harvesting trees for short-term uses, such as in paper, packaging and disposable chop sticks, does nothing for the atmosphere and, because of the low value of these products, encourages wasteful and destructive harvesting techniques.

There are many other good reasons for preserving the remaining areas of “pristine” vegetation, be they tropical rainforest, savanna grasslands or tundra, without trying to push the greenhouse argument.