Danish scientists say old-growth forests' climate role overestimated by 1/3

Incorrectly analyzed data led to mistaken view about the climate mitigation impact of old and unmanaged forests.

The claim that old-growth forests play a significant role in climate mitigation, based upon the argument that even the oldest forests keep sucking CO2 out of the atmosphere, is being refuted by researchers at the University of Copenhagen says a new report from Phys.org. The online science publications states that the argument – widely has been used widely to defend the withdrawal of forest management practices from treed areas, simply on the basis of age – depended on incorrectly analyzed data and that the climate mitigation effect of old and unmanaged forests has been greatly overestimated. 

Old and unmanaged  has become the subject of much debate in recent years, says the Phys.org report. "Setting aside forests as unmanaged has often been argued to play a significant role for climate mitigation," said the publication. But the argument "doesn't stand up," according to researchers at the University of Copenhagen, whose documentation has just been published as a commentary in Nature.

"The entire climate mitigation argument is based upon a widely cited 2008  which reports that old-growth forests continue to suck up and sequester large amounts of CO2 from the atmosphere, regardless of whether their trees are 200 years old or older," wrote Phys.org. "UCPH researchers scrutinized the article by reanalyzing the data upon which it was based. They conclude that the article arrives at a highly overestimated climate effect for which the authors' data presents no evidence."

In coastal British Columbia, old growth forest covers an area equal to 1.5 Vancouver Islands, or 4.4 million soccer fields, and three quarters of it is already protected in perpetuity. Because of climate change, trees that used to thrive in some areas will not do well in those locations over the long term. Old-growth preservation strategies that fail to consider climate create serious sustainability risks. 

Explained Per Gundersen, of the University of Copenhagen's Department of Geosciences and Natural Resource Management: "The climate mitigation effect of unmanaged forests with trees more than 200 years old is estimated to be at least one-third too high—and is based solely upon their own data, which, incidentally, is subject to great uncertainty. Thus, the basis for the article's conclusions is very problematic." 

Gundersen added: "Old-growth forest plays a key role in biodiversity. However, from a long-term climate mitigation perspective, it isn't an effective tool. Grasping the nuance is important so that debate can be based upon scientifically substantiated assertions, and so that policy is not influenced on an incorrect basis."

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