title: Old-growth forests as global carbon sinks.
abstract: Old-growth forests remove carbon dioxide from the atmosphere at rates that vary with climate and nitrogen deposition. The sequestered carbon dioxide is stored in live woody tissues and slowly decomposing organic matter in litter and soil. Old-growth forests therefore serve as a global carbon dioxide sink, but they are not protected by international treaties, because it is generally thought that ageing forests cease to accumulate carbon. Here we report a search of literature and databases for forest carbon-flux estimates. We find that in forests between 15 and 800 years of age, net ecosystem productivity (the net carbon balance of the forest including soils) is usually positive. Our results demonstrate that old-growth forests can continue to accumulate carbon, contrary to the long-standing view that they are carbon neutral. Over 30 per cent of the global forest area is unmanaged primary forest, and this area contains the remaining old-growth forests. Half of the primary forests (6 x 10(8) hectares) are located in the boreal and temperate regions of the Northern Hemisphere. On the basis of our analysis, these forests alone sequester about 1.3 +/- 0.5 gigatonnes of carbon per year. Thus, our findings suggest that 15 per cent of the global forest area, which is currently not considered when offsetting increasing atmospheric carbon dioxide concentrations, provides at least 10 per cent of the global net ecosystem productivity. Old-growth forests accumulate carbon for centuries and contain large quantities of it. We expect, however, that much of this carbon, even soil carbon, will move back to the atmosphere if these forests are disturbed.
authors.affiliation: Department of Biology, University of Antwerp, 2610 Wilrijk, Belgium. sebastiaan.luyssaert@ua.ac.be
authors.forename: Sebastiaan
authors.initials: S
authors.lastname: Luyssaert
authors.forename: E-Detlef
authors.initials: ED
authors.lastname: Schulze
authors.forename: Annett
authors.initials: A
authors.lastname: Börner
authors.forename: Alexander
authors.initials: A
authors.lastname: Knohl
authors.forename: Dominik
authors.initials: D
authors.lastname: Hessenmöller
authors.forename: Beverly E
authors.initials: BE
authors.lastname: Law
authors.forename: Philippe
authors.initials: P
authors.lastname: Ciais
authors.forename: John
authors.initials: J
authors.lastname: Grace
mesh_terms: D000818:Animals; D001272:Atmosphere / Q000737:chemistry; D018533:Biomass; D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D016208:Databases, Factual; D004190:Disasters; D017753:Ecosystem; D049668:History, 15th Century; D049669:History, 16th Century; D049670:History, 17th Century; D049671:History, 18th Century; D049672:History, 19th Century; D049673:History, 20th Century; D049674:History, 21st Century; D049690:History, Ancient; D049691:History, Medieval; D006802:Human Activities; D013997:Time Factors; D014197:Trees / Q000378:metabolism*
chemical_list: D002245:Carbon Dioxide; D002244:Carbon