Scientists have revealed that forests that are centuries old continue to remove carbon dioxide from the atmosphere. Up to now, the consensus was that these older forests were carbon-neutral. Since their growth was very slow, the release of carbon from dying vegetation and plant respiration was thought to be equal to the amount of carbon that is absorbed during photosynthesis. This theory is one of the reasons why unmanaged forests are not considered under the Kyoto protocol.
However, the researchers carried out a thorough analysis of decades of data on the carbon cycle - its removal from and release into the atmosphere - within old-growth forests. The findings suggest that these older forests continue to accumulate carbon.
The authors point out that, in fact, it is young forests rather than old-growth forests that can be sources of CO2, because their creation frequently disturbs soil and existing vegetation, either by natural or man-made processes. This causes decomposition of debris, litter and soil organic matter that all release carbon at a rate that exceeds the rate of growth and photosynthesis in younger trees.
In old forests, on the other hand, the release of CO2 from decomposing dead wood occurs over decades, whereas natural regeneration or in-growth occurs much more quickly. This means that as trees naturally die, new growth and the continued photosynthesis of living trees absorbs carbon more quickly than it is released.
There is currently no policy which specifically encourages old-growth forests to be left intact. This is, in part, due to the perception that the forests are carbon-neutral rather than absorbers of carbon. The design of climate change legislation also overlooks factors which would help protect old forests. For example, only anthropogenic effects on ecosystems are considered within the Framework Convention on Climate Change. Leaving forests intact is not perceived as an anthropogenic activity.
This new analysis draws attention to the urgent need to establish protection for old-growth forests. Old forests have accumulated vast quantities of carbon, which will further increase atmospheric CO2 concentrations if disturbed.