What was done
The authors examined the amount, quality and distribution of soil carbon below woody vegetation and grasses at three semiarid rangelands in the western United States.

What was learned
Both the total soil carbon and the amount of particulate organic matter were found to be significantly greater under woody plants than beneath adjacent grasses.

What it means
The range expansions of woody plants is often cited as one of the many consequences of the atmosphere's rising CO2 concentration.  Thus, as the air's CO2 concentration continues to rise, the expansion of woody plants onto grasslands should result in an increase in soil carbon sequestration, thereby slowing the rate of rise of the atmosphere's CO2 concentration.