In 1969, renowned American scientist E.P. Odum claimed carbon absorption in old-growth forests was balanced by the carbon the forest released. Odum was an environmental research pioneer, who championed the importance of "ecology" as a discipline. His old-forest theory was published in Science magazine that year, and provided models for related researches.

 

However, the theory is now challenged by a 400-year-old forest in south China, which soaked up more carbon than previously thought, according to a latest study published in Science last week.

 

The latest discovery may also make the preservation of old-growth forests forests of more than 100 years old a higher priority in carbon trading and other efforts to tackle global warming.

 

In the article, Chinese scientists demonstrated that the top 20 centimeters of soil in the old-growth forest of the Dinghushan Biosphere Reserve absorbed an unexpectedly high rate of atmospheric carbon from 1979 to 2003. "It (the carbon storage) increased by 0.61 tons a hectare annually," said Zhou Guoyi, the first author of the paper, who works at the South China Institute of Botany under the Chinese Academy of Sciences.

 

Zhou and his colleagues measured carbon in the soil collected from a studied area of seven hectares in the Dinghushan reserve, which lies 20 kilometers away from Guangzhou city proper.

 

They found organic carbon concentrations in the top 20 centimeters of the soil increased from about 1.4 per cent to 2.35 percent over that 24-year period.

 

"The finding can probably crack a current enigma confronting global scientific academia about carbon imbalance," said Zhou in an exclusive interview with China Daily.

 

What he refers to is an imbalance between the measured amount of carbon in the atmosphere and its theoretical estimate.

 

Zhou said scientists calculated the carbon quantity in the air based on the carbon released from burning fossil fuels, discharged from land-use change, and absorbed by oceans.

 

"The calculated result, however, is bigger than what scientists have measured," said the researcher.

 

"Something is missing in the measurement. One of the lost parts, as our study confirms, is the role of old-growth forest, which can absorb and store more greenhouse gases from the atmosphere than previously thought."

 

If the fact proves to be true with all old-growth forests in the world, it would explain a third of the "miscalculated" carbon storage.

 

The discovery will give developing countries, where old-growth forests are widespread, a "more powerful weapon" to argue for compensation from richer countries through global carbon trade, according to Zhou.

 

Carbon trade is a mechanism developed under the Kyoto Protocol's Clean Development Mechanism (CDM) to reduce global emission of carbon dioxide, the major greenhouse gas leading to global warming. Under the mechanism, industrialized countries pay developing nations for reducing the latter's carbon dioxide emissions and meeting their own emission limits.

 

Previous studies have testified that young forest can store large amounts of carbon.

 

"Trees in that ecosystem can reserve the amount of carbon equivalent to half of their increased biomass, let alone the soil in it, which can grab as much carbon as that of old-growth forest," Zhou said.

 

In November, the country started its first CDM project on forest carbon storage in the Guangxi Zhuang Autonomous Region with the sponsorship of World Bank.

 

The project plans to grow two 2,000-hectare forests in the region, which are expected to consolidate 500,000 tons of carbon dioxide within 15 years. "Based on our study, preservation of old-growth forest can also be seen a way of storing carbon and thus be traded," Zhou said.

 

Old-growth forest is mostly seen in tropical and subtropical developing countries. In China, this type of forest is distributed mostly in the southwestern and northeastern regions and along the Yarlung Zangbo River. A government report issued last year predicted that by 2010, the country's old-growth forest accumulation would stand approximately 3 billion cubic meters.

 

Li Yule, a domestic environmental expert, said the development of the large forest carbon exchange industry was a positive step, however foresaw barricades along the way.

 

"It is difficult to develop good methodology," said Li, who works at the Chinese Academy of Agricultural Sciences.

 

Moreover, rich countries were reluctant to become involved because "the forest may be chopped down one day after the project finishes," she said.

 

A World Bank report released in October estimates that deforestation accounts for 20 per cent of emissions of carbon dioxide worldwide annually.

 

The report also says that the potential benefits of using forests to store carbon dioxide have not been explored by the current carbon market, and urges for sustainable forest management to be integrated into the global strategy for reducing greenhouse gas emissions, according to UK-based science website portal SciDev.net.

 

Li hesitates to lend support to Zhou's opinion about the benefit of his research on carbon trade, since "old-growth forests account for too little an amount of carbon absorption based on the research," she explained.

 

She also added the current practice of CDM, which only includes forests planted after 1990 for carbon trading, also limits the application of Zhou's theory in this field.

 

However, despite a detection of carbon storage increase in old-growth forest, Zhou and his colleagues are not yet clear about the driving forces behind it.

 

But the researcher puts forward his three assumptions.

 

"The unusual carbon storage increase must come from a restrained effect of micro-organism, which is supposed to decompose organic matter in the soil to unlock carbon," Zhou said.

 

He estimated the increased acid deposition in the air and growing proportion of nitrogen to phosphorus in the soil, both due to industrial pollution, might have curbed the activities of micro-organism.

 

In addition, the rising temperature resulting from global warming may have grabbed away more water from the soil and restrained the speed of soil degradation process.

 

"In our studied area, the temperature has risen by 0.6C in recent three decades," the researcher said.

 

Though in short of funding, Zhou said he would continue further analysis about these hypotheses by conducting more studies.

 

(China Daily December 5, 2006)