Re-evaluation of forest biomass carbon stocks and lessons from the world's most carbon-dense forests

Abstract

From analysis of published global site biomass data (n ‫؍‬ 136) from primary forests, we discovered (i) the world's highest known total biomass carbon density (living plus dead) of 1,867 tonnes carbon per ha (average value from 13 sites) occurs in Australian temperate moist Eucalyptus regnans forests, and (ii) average values of the global site biomass data were higher for sampled temperate moist forests (n ‫؍‬ 44) than for sampled tropical (n ‫؍‬ 36) and boreal (n ‫؍‬ 52) forests (n is number of sites per forest biome). Spatially averaged Intergovernmental Panel on Climate Change biome default values are lower than our average site values for temperate moist forests, because the temperate biome contains a diversity of forest ecosystem types that support a range of mature carbon stocks or have a long land-use history with reduced carbon stocks. We describe a framework for identifying forests important for carbon storage based on the factors that account for high biomass carbon densities, including (i) relatively cool temperatures and moderately high precipitation producing rates of fast growth but slow decomposition, and (ii) older forests that are often multiaged and multilayered and have experienced minimal human disturbance. Our results are relevant to negotiations under the United Nations Framework Convention on Climate Change regarding forest conservation, management, and restoration. Conserving forests with large stocks of biomass from deforestation and degradation avoids significant carbon emissions to the atmosphere, irrespective of the source country, and should be among allowable mitigation activities. Similarly, management that allows restoration of a forest's carbon sequestration potential also should be recognized.Eucalyptus regnans ͉ climate mitigation ͉ primary forest ͉ deforestation and degradation ͉ temperate moist forest biome D eforestation currently accounts for Ϸ18% of global carbon emissions and is the third largest source of emissions (1). Reducing emissions from deforestation and degradation (REDD) is now recognized as a critical component of climate change mitigation (2). A good understanding of the carbon dynamics of forests (3) is therefore important, particularly about how carbon stocks vary in relation to environmental conditions and human land-use activities. Average values of biomass carbon densities for the major forest biomes (4) are used as inputs to climate-carbon models, estimating regional and national carbon accounts, and informing policy debates (5). However, for many purposes it is important to know the spatial distribution of biomass carbon within biomes (6) and the effects of human land-use activities on forest condition and resulting carbon stocks (refs. 3 and 7 and www-.fao.org/forestry/site/10368/en).Primarily because of Kyoto Protocol rules (ref. 8; http:// unfccc.int/resource/docs/convkp/kpeng.pdf), interest in carbon accounting has been focused on modified natural forests and plantation forests. It has been argued that primary forests, especially very old forests, a...

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