Old-growth forests are ecologically significant due to their biodiversity and distinct biological features. They often house rare to endangered species of animals and plants, and they have a large range of vegetation. Despite their unique beauty, they are frequently left unprotected, in part because they are commonly considered to be either carbon neutral or contributors to global warming. That long-held view is being contradicted in a recent issue of Nature by a team of scientists from Belgium, Germany, Switzerland, France, the United Kingdom, and the United States.
The scientists examined data from 519 studies to look at how much CO2 is assimilated by old-growth forests and compared that with the amount that is released through decomposition and respiration. They focused their efforts on boreal and temperate forests, while excluding tropical forests due to a lack of available data.
The overall conclusion of their work is that forests between 15 and 800 years old are CO2 sinks. However, the probability that a forest actually becomes a source of carbon does increase with age. A 60 year old forest has a 20 percent chance of being a carbon source, while a 300 year old forest has a 35 percent probability. Nevertheless, on average, every hectare of old-growth forest sequesters around 5291 pounds (2400 kilograms) of carbon every year.
Although old-growth forests are carbon sinks, they do have a lot of accumulated carbon from centuries of life. Thus, it is extremely important that they remain undisturbed, or all that stored carbon can be released into the environment.
Old-forests represent roughly 15 percent of the world's forests and accounts for at least 10 percent of the net carbon balance, so they are valuable for the well-being of our environment. They are not currently singled out for protection under international treaties, an oversight that should be carefully evaluated.
Nature, 2008. DOI: 10.1038/nature07276