Forests suck more CO2 during drought

forestsClimate models have been turned upside down by a research finding that US forests sucked CO2 from the atmosphere ­despite being in the grip of one of the nation’s worst droughts.

New modelling of carbon take-up during 2012 has con­cluded that the country’s flora ­absorbed more carbon than it emitted, at a time when the most severe drought since the 1930s, a notorious dry spell known as the Dust Bowl period, was enveloping most of the US mainland.

The finding questions conventional wisdom that drought turns terrestrial flora from a sink into a carbon source, as expiring plants release trapped CO2 into the atmosphere.

The team, led by scientists from the University of California and ETH Zurich in Switzerland, concluded that accelerated growth during the preceding spring — the warmest ever in the US — had acted as a buffer against the summer. “The ­increase in carbon uptake during the warm spring compensated for the reductions in uptake during the drought,” said lead researcher Sebastian Wolf.

The researchers found the higher spring temperatures had triggered earlier growth of trees, grasses and crops, which had ­absorbed more carbon than they would during a normal spring.

The revelation, published today in the Proceedings of the National Academy of Sciences, ­coincides with the release of separate research showing that increased CO2 levels over the past 33 years have helped generate the equivalent of an extra 18 million square kilometres of forest.

The study found the Appalachian forests of the southeastern US had been a particularly effective carbon sink. Uptake in the midwestern plains had been more muted, leaving the region “close to carbon neutral”.

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