Soils in newly forested areas store substantial carbon that could help offset climate change

Apr 01, 2013
Forest plantations established on formerly non-forested land, like this experimental poplar stand in Michigan's Upper Peninsula, accumulate soil carbon that helps to offset carbon emissions and climate change. Credit: Ray Miller

Surface appearances can be so misleading: In most forests, the amount of carbon held in soils is substantially greater than the amount contained in the trees themselves.

If you're a land manager trying to assess the potential of forests to offset carbon emissions and climate change by soaking up and storing it, what's going on beneath the surface is critical.

But while scientists can precisely measure and predict the amount of above-ground carbon accumulating in a forest, the details of soil-carbon accounting have been a bit fuzzy.

Two University of Michigan researchers and their colleagues helped to plug that by analyzing changes in soil carbon that occurred when trees became established on different types of nonforested soils across the United States.

In a paper published online April 1 in the Soil Science Society of America Journal, they looked at lands previously used for surface mining and other industrial processes, former agricultural lands and where forests have encroached.

U-M ecologist Luke Nave and his colleagues found that, in general, on formerly nonforested land increases soil carbon. Previous studies have been equivocal about the effects of so-called afforestation on soil carbon levels.

"Collectively, these results demonstrate that or allowing them to establish naturally on nonforested lands has a significant, positive effect on the amount of carbon held in soils," said Nave, an assistant research scientist at the U-M Biological Station and in the Department of Ecology and .

"These represent a significant carbon reservoir that is helping to offset that lead to climate change," said Nave, lead author of the paper.

Large and rapid increases in soil carbon were observed on forested land that had previously been used for surface mining and related industrial processes. On a post-mining landscape, the amount of soil carbon generally doubled within 20 years of mining termination and continued to double every decade or so after that.

The changes after cultivated farm fields were abandoned and trees became established are much subtler, though still significant. This type of tree establishment—which has been widespread in recent decades in the northeastern United States and portions of the Midwest—takes 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.

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Feldagast
3 / 5 (4) Apr 01, 2013
Could the deforestation and burning of the tropical rainforests have anything to do with global warming?
Maggnus
2.8 / 5 (5) Apr 01, 2013
Could the deforestation and burning of the tropical rainforests have anything to do with global warming?


Not much, actually. There is argument that deforestation results in less carbon sequestration, and more carbon release from the burning, however that seems to be pretty well offset by other conditions (such as microbial growth in the soil, among others) whichs leaves a net balance.

Furthermore, it appears that net carbon uptake by forests actually tapers off as more carbon is added to the atmosphere and the average temperature goes up.
ValeriaT
2.3 / 5 (6) Apr 01, 2013
Could the deforestation and burning of the tropical rainforests have anything to do with global warming?
IMO yes. The forests hold precipitate watter which evaporates in clouds and reflects the light. Without forests all water will drain back into sea fast again. The deforestation is the main factor of deserts spreading, the desert spreading increases the spreading of droughts at the inland. It's positive feedback because of high latent heat of water held with forests. BTW The forests may appear darker than the soil at the first look, but they're actually much lighter for infrared portion of spectrum, which represents the main portion of the heat flux from Sun. The leaves do behave like the infrared mirrors for the heat.
grondilu
2.1 / 5 (7) Apr 01, 2013
There is a nice speech from Freeman Dyson available on YouTube! and called "heretic thoughts about science and society" where he defends the idea that global warming issues are grossly exaggerated and that it's basically a matter of land management. It's the first time I read a phys.org article that seems to go in this direction and uses the expression "land management".
deepsand
2.7 / 5 (7) Apr 02, 2013
BTW The forests may appear darker than the soil at the first look, but they're actually much lighter for infrared portion of spectrum, which represents the main portion of the heat flux from Sun.

IR is a minority of Solar influx.
mother nature son
1.7 / 5 (3) Apr 02, 2013
reducing the paved roads,streets and highways and putting more bushes and trees in the cities and urban areas could help reduce CO2,wouldn't it? I think the Earth,s surface is like skin,it breathes through the air. Hope you'll understand what I mean.
ricker
3 / 5 (1) Apr 03, 2013
With respect to soil carbon increases in areas where trees and shrubs have encroached on native grasslands: It seems to me that "largely due to the suppression of wildfires" is a key phrase here. We're learning, the hard way, that fire suppression, generally, has led to more and hotter fires in the long run due to the amount fuel left on the ground. Such fires tend to burn deeper and put more surface and subsurface carbon into the atmosphere, yes? Global warming is also exacerbating that problem. Under such circumstances we should be careful about the conclusions we draw from this research.

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