The benefit of old-growth forests

Old-growth forests appear to be far more active in taking up atmospheric carbon dioxide than previously believed.

At least that’s the take of an international team led by University of Antwerp biologist Sebastiaan Luyssaert. If their results hold up to further scrutiny, they could touch off an energetic climate-policy debate. Under the 1997 Kyoto Protocol, developed countries are not allowed to take credit for emissions reductions provided by existing forests. These countries were to take “additional” measures beyond what they or their trees may have already been doing. Yet to get developing countries involved in a new global climate agreement, currently being negotiated, one of the leading ideas calls for giving developing country credit for “avoided deforestation.” The idea that old-growth forests in some regions may also be actively soaking up CO2 for far longer than previously believed, could reopen the discussion of developed countries claiming credit for the atmospheric cleanup work of existing forests.

Past researchers looked at individual markers such as a forests’ net primary productivity – a measure of the CO2 plants take up and give off. By that measure, old-growth forests were held to be carbon-neutral when they matured. They may lock up carbon for long periods, but the CO2 they soak up is offset by the CO2 they give off. Dr. Luyssaert’s team looked at boarder measures, including net ecosystem productivity. They found that the world’s old-growth forests – which are up to 800 years old and constitute 15 percent of global forest cover – sequester about 1.3 billion tons of carbon every year.

Results appear in today’s issue of the journal Nature.