Proceedings of the National Academy of Sciences USA

PNAS February 5, 2008 vol. 105 no. 5 1551-1555

OPEN ACCESS ARTICLE http://www.pnas.org/cgi/content/full/105/5/1551

Risk of natural disturbances makes future contribution of Canada's forests to the global carbon cycle highly uncertain

Werner A. Kurz, Graham Stinson, Gregory J. Rampley, Caren C. Dymond, and Eric T. Neilson

Abstract

A large carbon sink in northern land surfaces inferred from global

carbon cycle inversion models led to concerns during Kyoto Protocol

negotiations that countries might be able to avoid efforts to reduce

fossil fuel emissions by claiming large sinks in their managed

forests. The greenhouse gas balance of Canada's managed forest is

strongly affected by naturally occurring fire with high interannual

variability in the area burned and by cyclical insect outbreaks.

Taking these stochastic future disturbances into account, we used the

Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3) to

project that the managed forests of Canada could be a source of

between 30 and 245 Mt CO2e yr-1 during the first Kyoto Protocol

commitment period (2008-2012). The recent transition from sink to

source is the result of large insect outbreaks. The wide range in the

predicted greenhouse gas balance (215 Mt CO2e yr-1) is equivalent to

nearly 30% of Canada's emissions in 2005. The increasing impact of

natural disturbances, the two major insect outbreaks, and the Kyoto

Protocol accounting rules all contributed to Canada's decision not to

elect forest management. In Canada, future efforts to influence the

carbon balance through forest management could be overwhelmed by

natural disturbances. Similar circumstances may arise elsewhere if

global change increases natural disturbance rates. Future climate

mitigation agreements that do not account for and protect against the

impacts of natural disturbances, for example, by accounting for forest

management benefits relative to baselines, will fail to encourage

changes in forest management aimed at mitigating climate change.

Complete article at http://www.pnas.org/cgi/content/full/105/5/1551-

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