Forest Soil Traps More Carbon Than Thought
April 1, 2013

New Forest Dirt Traps Lots Of Carbon, May Help Curb Climate Change

Brett Smith for — Your Universe Online

The planting and expansion of forests not only allows for the trapping of carbon in the trees themselves, it also fosters carbon absorption in the soil where the trees are rooted.

Previous studies have shown that more carbon is sequestered in forest soils that in the trees, but according to new research in“¯the“¯Soil Science Society of America Journal, newly forested lands show a marked increase in carbon sequestration as the trees begin to take root and grow — a fact which could help to curb the effects of global climate change.

To reach their conclusion, researchers from several midwestern universities culled data from 39 papers published between 1957 and 2010. They found significant increases in soil carbon on forested land that had previously been used for agriculture, surface mining and other human activities. On post-mining landscape, the amount of soil carbon approximately doubled within 20 years of activity stopping and continued to double approximately every ten years after that.

"Collectively, these results demonstrate that planting trees or allowing them to establish naturally on non-forested lands has a significant, positive effect on the amount of carbon held in soils," said co-author Luke Nave from the Department of Ecology and Evolutionary Biology at the University of Michigan. "These forest soils represent a significant carbon reservoir that is helping to offset carbon emissions that lead to climate change.”

The team found that the changes to former farmers´ fields where trees have encroached are subtler but still significant. The entire reclamation process, including the boosting of carbon sequestration, takes about 40 years to produce noticeable results. After 100 years, carbon content in the soil averages about 15 percent higher than when the land was under cultivation, with the upper two inches of the soil representing the most significant change.

The team also found changes made to land that were former grasslands and found that soil carbon increased 31 percent after several decades. They noted that this kind of forest incursion is happening throughout the Great Plains due to improved wildfire-fighting capabilities.

The scientists said that their study could be used to influence policymakers charged with making decisions about land use.

"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.

The team´s findings resonate with another recent study which found that large underground networks of fungi may sequester large amounts of carbon in forests. Looking at forested lands in Sweden, the international team of researchers found that the Mycorrhizal fungi which live in and on tree roots underground hold as much as 50 to 70 percent of the total carbon stored in leaf debris and soil.

The two studies challenge long-held theories that forest carbon accumulates mostly above ground in forest detritus. The researchers in the Swedish study suggest that trees direct carbon deeper into the soil using their root systems.

“People talk about how plants shuttle half their carbon to the belowground root system, but it has kind of been neglected in carbon storage models,” said study co-author Karina Clemmensen, a fungal ecologist at the Swedish University of Agricultural Sciences in Uppsala.