The changes after cultivated farm fields were abandoned and trees became established are much subtler, though still significant. This type of tree establishmentwhich has been widespread in recent decades in the northeastern United States and portions of the Midwesttakes about 40 years to cause a detectable increase in soil carbon.
But at the end of a century's time, the amount of soil carbon averages 15 percent higher than when the land was under cultivation, with the biggest increases (up to 32 percent) in the upper two inches of the soil.
In places where trees and shrubs have encroached into native grassland, soil carbon increased 31 percent after several decades, according to the study. That type of incursion is occurring throughout the Great Plains, from the Dakotas all the way to northern Texas, and is largely due to suppression of wildfires.
"Our work helps those tasked with understanding and managing the carbon balance of U.S. lands by putting a number on the changes in soil carbon that occur during this sort of land-use transition," Nave said.
Most of the organic carbon in forest soils comes from the growth and death of roots and their associated fungi, he said.
|Contact: Jim Erickson|
University of Michigan