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

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http://www.pnas.org/content/106/28/11635.full?sid=e40181cb-b476-4a83-9e17-58e56d7a263e

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

Heather Keith,1,
Brendan G. Mackey and
David B. Lindenmayer

+Author Affiliations

1. The Fenner School of Environment and Society, Australian National University, Canberra, ACT 0200, Australia

Communicated by Gene E. Likens, Cary Institute of Ecosystem Studies, Millbrook, NY, March 9, 2009 (received for review July 14, 2008)

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.

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Climate Change Policy Implications

Our results about the magnitude of carbon stocks in forests, particularly in old forests that have had minimal human disturbance, are relevant to negotiations under the United Nations Framework Convention on Climate Change (UNFCCC) concerning reducing emissions from deforestation and forest degradation. In particular, our findings can help inform discussions regarding the roles of conservation, sustainable management of forests and enhancement of forest carbon stocks (ref. 61; http://unfccc.int/resource/docs/2007/cop13/eng/06a01.pdf#page=8 ). 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 negotiated through the UNFCCC for the post-2012 commitment period. Similarly, where practical, management that allows restoration of a forest's carbon sequestration potential should be a recognized mitigation activity.

Our insights into forest types and forest conditions that result in high biomass carbon density can be used to help identify priority areas for conservation and restoration. The global synthesis of site data (Fig. 3 and Table 2) indicated that the high carbon densities of evergreen temperate forests in the northwestern United States, southern South America, New Zealand, and southeastern Australia should be recognized in forest biome classifications.

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