I am not sure that is true. There has been some change in opinion on whether old growth continues to be a carbon sink. I don't have a good ref handy, but found

I am not sure that is true. There has been some change in opinion on whether old growth continues to be a carbon sink. I don't have a good ref handy, but found this: "Until recently it was believed only young forests sequestered atmospheric carbon in early growth and that old-growth forests were only sinks in which the carbon was stored. Recent studies, however, have identified that intact old-growth forests continue to take up carbon from the atmosphere even past the point at which they reach maturity. By measuring growth rates, researchers have identified that carbon sequestration in trees increases continuously because the overall leaf area increases as they grow, enabling bigger trees to absorb more carbon from the atmosphere. Older, larger deciduous trees reproduce more new leaves, thus capturing the most carbon from the atmosphere." http://www.futuredirections.org.au/publication/role-old-growth-forests-carbon-sequestration/ http://www.futuredirections.org.au/publication/role-old-grow...