Published online 19 August 2009 | Nature | doi:10.1038/news.2009.842

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Forest definition comes under fire

Ecologists accuse framework convention of barking up the wrong tree.

ForestEcologists have questioned the UNFCCC's definition of a forest.Punchstock

The health of the world's forests — and their capacity to lock away carbon — could be jeopardized by logging if the United Nations Framework Convention on Climate Change (UNFCCC) definition of a forest is not changed, a study warns.

A future climate deal could see developing countries financially compensated for preserving their forests. The UNFCCC defines a forest as an area of land 0.05–1 hectare in size, of which more than 10–30% is covered by tree canopy. Trees must also have the potential to reach a minimum height of 2-5 metres.

Countries participating in the UNFCCC can choose how they want to define a forest from within those ranges. For example, in Brazil a forest is defined as an area of land greater than 1 hectare, with more than 30% canopy cover and a minimum tree height of 5 metres. By contrast, Ghana defines a forest as an area of land greater than 0.1 hectare, with more than 15% canopy cover and a minimum tree height of 2 metres.

But a report1 in the journal Conservation Letters, says that the UNFCCC has set the proportion of land that must be covered by tree canopy too low. Nophea Sasaki, a forest ecologist at Harvard University, and an author of the study, says that woodland could be "severely degraded" but still be classified as a forest under the current UNFCCC definition.

“Our main concern is that people will take it as a threshold and keep logging until they reach it.”

Nophea Sasaki
Harvard University

"Our main concern is that people will take it as a threshold and keep logging until they reach it," he says. So even though the region could lose a lot of biodiversity and a large proportion of its carbon stock, it would still be regarded as a forest. Sasaki says that loggers tend to target the bigger, more mature tree species, which hold the most carbon.

In a case study of an evergreen forest in Cambodia, Sasaki and his co-author Francis Putz from the University of Florida in Gainsville use inventory data for plots of trees with trunks wider than 5 centimetres to estimate that the forest holds 121.2 tonnes of carbon per hectare. Of this, 71.4 tonnes is in trees that have trunks wider than 45 centimetres — the trees that loggers are most likely to target. So if all these larger trees were harvested, the carbon stock would be depleted by almost 40%, yet the forest would still be considered a forest under the UNFCCC definition, the study says.

Copenhagen concerns

Sasaki says that the minimum threshold for canopy cover should be raised to 40%, the minimum tree height should be 5 metres and that natural forests should be differentiated from plantations.

His proposed threshold for canopy cover, he says, is based not on calculations that show forest degradation would be avoided at these levels, but rather on the definition used by the Food and Agriculture Organization of the United Nations, as this is likely to be acceptable to participating countries and "40% has to be better than 30%".

Sasaki is also concerned that forest degradation will be "disregarded" in the post-Kyoto agreement on climate change due to be negotiated in Copenhagen in December. But Sasaki says that several prominent studies ignore the issue of degradation of forests and their long-term sustainability — including a report2 from the Harvard University project on international climate agreements which was presented to the UNFCCC in Poznań, Poland, in December last year.

Neil Burgess, a conservation scientist at the University of Cambridge, UK, says that part of the problem is that degradation is not easy to measure. Unlike deforestation, which can be measured by remote-sensing methods such as satellites, degradation is evaluated through on-the-ground studies that assess what types of tree species are growing and estimate the forest's carbon stock.

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Burgess says Sasaki's paper has not proven why its proposed definition of a forest would be optimal, but that "the more canopy cover you have, the more intact the forest is, so the more carbon it is retaining".

"Working out the amount of degradation that would be tolerable in a post-Kyoto agreement would be useful. People at the Copenhagen meeting will have to worry about this to some extent," Burgess says. 

  • References

    1. Sasaki, N. & Putz, F. E. Conserv. Lett. advance online publication doi:10.1111/j.1755-263x.2009.00067.x (2009).
    2. Aldy, J. E. & Stavins, R. N. Designing the Post-Kyoto Climate Regime: Lessons from the Harvard Project on International Climate Agreements (Harvard Project on International Climate Agreements, 2008).
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