The team measured carbon-dioxide uptake in the forest over five years, from 2006–2010, with the tower-based eddy covariance approach. In non-drought years each square metre of forest took up between 100 and 200 grams of carbon annually, but in 2009 annual uptake was around zero because extreme dryness stopped photosynthesis in late summer, normally a period of high carbon uptake. Annual carbon-dioxide uptake over this time period was also measured to be roughly zero at a nearby site that had switched from being a forest to sparse grassland following an intense forest fire a decade earlier.

The results highlight how vulnerable semi-arid forests can be when it comes to carbon sequestration during periods of extreme drought, aridity and fires, which are predicted to increase greatly with climate change in many regions. Strategies to mitigate the impacts of extreme droughts, such as forest thinning to increase water supply to vegetation and active reforestation after intense burning with arid-adapted trees, are being developed and evaluated.

• The paper is part of the ERL Focus on Extreme Events and the Carbon Cycle.

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