Forests are a great bulwark against climate change, so programs to reduce deforestation are important. Those efforts usually focus on stopping the destruction in areas where it is already occurring.
But a new study suggests these programs would do well to also to preserve forests where deforestation and degradation have not begun. Gradual loss of these largely pristine, intact forests has a much greater climate effect than previously accounted for, the researchers said.
Globally, forests take more than a quarter of the carbon emissions from human activities out of the atmosphere every year. Intact forests are especially effective at storing carbon — although only about 20% of tropical forests are considered relatively pristine, they are responsible for about 40% of carbon storage in the tropics.
The study, by researchers from the Wildlife Conservation Society, the University of Queensland in Australia and other institutions, analyzed carbon emissions from the loss of intact tropical forests worldwide from 2000 to 2013.
Immediate clearing of intact forests, what might be considered "classic" deforestation, over that period accounted for about 3% of global emissions from deforestation in all tropical forests, the researchers said. But when they looked at other, more gradual types of loss and disturbance — forests that had been opened to selective logging for firewood, for example, or road-building that exposed more trees to drying or windy conditions — they found that the carbon effect increased sixfold over the period.
"It's alarming, because there are huge amounts of intact forest being disturbed every year," said Tom Evans, who leads the forest conservation program at the Wildlife Conservation Society and was a co-author of the paper, which was published in Science Advances. Worldwide in the first 15 years of the 21st century, about 9% of intact forests were opened up to degradation and deforestation.
The study amounts to a more complete accounting of the carbon effect of forest loss. Some of the effect comes not from newly accounted for emissions but from what the researchers called "forgone removals" — a degraded or disturbed forest takes up less carbon from the atmosphere than a fully intact one.
"These forests are working for us each year, soaking up large amounts of carbon," Evans said. "But we don't account for that when the damage happens."
International programs like Reducing Emissions from Deforestation and Forest Degradation, or REDD, are seen as a way to help limit global warming by using financial incentives to halt ongoing deforestation, thus conserving forests' carbon-storing capabilities.
But Evans said the new study showed that protecting still-undamaged forests could have a strong climate benefit as well.
"From a number of different angles there's a rising realization that we need to do more than just the core REDD approach," Evans said.
For one thing, if preserving an intact forest has a climate effect six times greater than previously thought, perhaps the financial incentive to preserve it should be substantially higher, he said.
"I'm not sure the answer is to change REDD," Evans added. "I suspect there's probably some complementary approach that can be used."