Bigger trees means bigger carbon sink

By identifying, mapping and measuring the trunks of 70,000 trees across Africa, geographers from the University of Leeds Earth and Biosphere Institute have found that tropical forests are soaking up more carbon dioxide

In research published in Nature, lead author Dr Simon Lewis and his team measured trees in 79 areas of intact tropical forest in ten African countries and combined their findings with those of South American and Asian studies – a combined total of 250,000 tree records – to assess the total carbon sink of tropical forests. They found that, compared with the 1960s, each hectare of intact African forest trapped an extra 0.6 tonnes of carbon per year. Their estimates suggest that in total, the world’s tropical forests remove 4.8 billion tonnes of CO2 from the atmosphere each year.

‘We are receiving a free subsidy from nature,’ said Lewis. ‘Tropical forest trees are absorbing about 18 per cent of the CO2 added to the atmosphere each year from burning fossil fuels, substantially buffering the rate of climate change.’

The reason for the trees’ increase in size is unclear, but Lewis suspects that higher CO2 levels may be stimulating growth. ‘Whatever the cause, we can’t rely on this sink forever,’ he said. ‘Even if we preserve all remaining tropical forest, these trees won’t continue getting bigger indefinitely.’

April 2009