Trees Getting Bigger Absorbing More Carbon

Picture of Huge Tree in African Forest

Forest trees are getting bigger and absorbing more carbon (CIFOR)
An international team of scientists, including researchers from CIFOR, have discovered that rainforest trees are getting bigger, storing more carbon from the atmosphere and slowing climate change.

According to the findings, tropical trees in undisturbed forests around the world are absorbing nearly a fifth of the carbon-dioxide (C02) released by burning fossil fuels. That is significantly more than the greenhouse gas emissions produced by the world’s transport sector.

The researchers estimate that remaining tropical forests remove a massive 4.8 billion tonnes of CO2 emissions from the atmosphere each year. This includes a previously unknown carbon sink in Africa, mopping up 1.2 billion tonnes of CO2 each year.

Published on February 19 in Nature, the 40-year study of African tropical forests, which account for one third of the world’s total tropical forest, shows that over decades each hectare of intact African forest has trapped an extra 0.6 tonnes of carbon per year.

Combined with data from South America and, to a lesser extent, from Asia, the study’s analysis of the records of 250,000 trees reveals that, on average, remaining undisturbed forests are trapping carbon and thus constitute a globally significant carbon sink.

According to the report’s lead author, Dr. Simon Lewis from the University of Leeds, "Tropical forest trees are absorbing about 18% of the CO2 added to the atmosphere each year from burning fossil fuels, substantially buffering the rate of climate change."

The reason why the trees are getting bigger and mopping up carbon is unclear. A leading suspect is the extra CO2 in the atmosphere itself, which may be acting like a fertiliser. However, Dr Lewis warns, "Whatever the cause, we cannot rely on this sink forever. Even if we preserve all remaining tropical forest, these trees will not continue getting bigger indefinitely."

The Intergovernmental Panel on Climate Change reports that human activity emits 32 billion tonnes of CO2 each year globally, but only 15 billion tonnes actually stays in the atmosphere adding to climate change. The new research shows where some of the ‘missing’ 17 billion tonnes per year is going.

"It’s well known that about half of the ‘missing’ carbon is being dissolved in to the oceans, and that the other half is going somewhere on land in vegetation and soils, but we were not sure precisely where. According to our study about half the total carbon ‘land sink’ is in tropical forest trees," explains Dr Lewis.

One of the report’s co-authors, Dr. Douglas Sheil from the Center for International Forestry Research and Uganda’s Institute of Tropical Forest Conservation, says he had previously been unconvinced about the role forests play in removing carbon-dioxide from the atmosphere.

Dr. Sheil said that “prior to working on the report, I was like many scientists who used to dismiss the campaigners’ slogan that forests are the lungs of the world. We believed that forests were basically in equilibrium with the atmosphere, neither adding to nor subtracting from its gaseous composition.”

“Our findings give the lungs-metaphor a basis after all: forests draw CO2 from the biosphere just as our lungs remove it from our bodies. Though of course, trees absorb carbon-dioxide while people expel it,” Dr. Sheil said.

CIFOR colleague and fellow co-author, Dr. Terry Sunderland, says that while there is no question rainforest trees are getting bigger and storing more CO2, it is vital that more carbon up-take studies like those in Africa and South America are carried out in Asia.

“The data from Asia exists and it supports the same conclusions arrived at in places like the Amazon and the Congo Basin,” Dr. Sunderland said, “But the Asian data is not as long term as it is in Africa or South America.”

According to Dr. Sunderland, carbon up-take studies are particularly important for Indonesia.
“Indonesia is deeply interested in REDD and carbon payment schemes, yet deforestation in Indonesia is contributing to the country’s status, according to some estimates, as the world’s third largest emitter of greenhouse gases1.
“If carbon payment schemes such as REDD are to succeed in Indonesia, they must be based on accurate assessments of the amount of carbon stored in the country’s forests. These calculations need to be based on local and realistic figures,” Dr. Sunderland said.

The report’s implications for future carbon payment schemes are echoed in the comments of another of the report’s co-authors, Dr Lee White, Gabon’s Chief Climate Change Scientist.

“The removal of nearly 5 billion tonnes of carbon dioxide from the atmosphere by intact tropical forests, based on realistic prices for a tonne of carbon, should be valued at around £13 billion per year. This is a compelling argument for conserving tropical forests," Dr. White said.

According to Dr. Lewis, rich polluting countries can assist with conserving forests by “transferring substantial resources to countries with tropical forests to reduce deforestation rates and promote alternative development pathways.”
Dr. Sunderland cautions that any investment in REDD or similar carbon payment schemes must first formalize and enforce land rights for forest dwellers.

“It’s absolutely essential that a significant proportion of any payments for environmental services, such as REDD payments, are made to those who rely on forests for their well-being. After all, up to a billion of the world’s poorest people rely on forests in one way or another for their livelihoods,” Dr. Sunderland said.

*Adapted with permission from “One-fifth of fossil-fuel emissions absorbed by threatened forests”, University of Leeds media release.

www.cifor.cgiar.org/publications/pdf_files/media/Rsch_paper_AfricanFores...
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