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Dryland Ecosystems Drivers of Global Carbon Cycle

May 22, 2014 03:18 PM EDT
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New research has found that dryland ecosystems, from deserts to dry-shrublands, play a more important role in the global carbon cycle than previously thought, and in fact are drivers of this process.

"Our study found that natural events in Australia were largely responsible for this anomaly," Montana State University faculty member Ben Poulter said in a press release. "La Nina-driven rainfall during 2010 and 2011, as well as the 30-year greening up of its deserts and other drylands contributed to significant changes across the globe."

Poulter and his colleagues realized that the world's land carbon sink in 2011 seemed to be absorbing an unusually large amount of carbon. Carbon constantly moves between land, oceans, vegetation and the atmosphere. It is when one of these absorbs more carbon dioxide than it releases that it is referred to as a "carbon sink."

Investigating this phenomenon, researchers eventually discovered that over the past 30 years dryland regions sprouted more vegetation in response to precipitation, which in itself doesn't seem that important. But the study team noted that the correlation between desert greening and climate extremes grew noticeably significant over the years.

Dryland systems in the Southern Hemisphere, particularly Australia, had high productivity in response to increased La Nina-phase rainfall.

"What surprised us was that no analogous biosphere response to similar climatic extremes existed in the past 30 years, prompting us to explore whether documented dryland-greening trends were responsible for changes in the carbon cycle dynamics," commented co-author Philippe Ciais.

Between the periods of 1982-1996 and 1997-2011 drylands became particularly sensitive to precipitation, resulting in a four-fold increase in net carbon uptake these past 30 years.

However, researchers note the 2011 carbon uptake is not expected to lead to long-term increases in ecosystem carbon accumulation.

"Dryland systems have high rates of carbon turnover compared to other biomes," Ciais added. "We can expect the carbon to be quickly respired or consumed in wildfires, already partly reflected by the high atmospheric carbon dioxide growth rate in 2012."

The findings were published in the journal Nature.

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