Apr 4, 2013
Insight: drought 'turns off' carbon sequestration in forests
Short-term drought appears to reduce dramatically how much carbon is sequestered in semi-arid forests, according to a team of researchers at the School of Forestry at Northern Arizona University, US. Thomas Kolb, Sabina Dore and Mario Montes-Helu, who report their results in Environmental Research Letters, said that an unusual late-summer drought and hot spell that occurred in 2009 flipped the carbon sequestration "switch" from on to off for a ponderosa pine forest in Arizona.
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.
About the author
Thomas Kolb is professor of forest ecophysiology in the School of Forestry, Northern Arizona University, US. As well as teaching, his research interests focus on threats to forest goods and services from stress, including climate change. Sabina Dore and Mario Montes-Helu were research associates in the School of Forestry when the work described in this article was carried out. Dore is now a research associate at the University of California, Berkeley, US, and Montes-Helu is assistant professor at Northern New Mexico College, US.