Forest soils lose carbon in a warming world

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In Massachusetts, the world’s longest-running experiment to discover how warming temperatures affect forest soils has revealed that soil warming stimulates periods of abundant carbon release from the soil to the atmosphere alternating with periods of no detectable loss in soil carbon stores.

This experiment began in 1991 in a deciduous forest stand at the Harvard Forest. Electrical cables were buried in a set of plots and heated the soil 5 degrees Celsius above the ambient temperature of control plots. Over the course of the 26-year experiment, the warmed plots lost 17 percent of the carbon that had been stored in organic matter in the top 60 centimeters of soil.

The results indicate that in a warming world, a self-reinforcing and perhaps uncontrollable carbon feedback will occur between forest soils and the climate system, adding to the build-up of atmospheric carbon dioxide caused by burning fossil fuels and accelerating global warming.