Insects Turn Canada’s Forests From Carbon Sinks to Carbon Sources

“The recent transition from sink to source
is the result of large insect outbreaks.”

Proceedings of the National Academy of Sciences USA

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


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


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.

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