Column: How the Hoosier National Forest can help on climate change

Climate change is already evident in Indiana in the form of warmer winters, drier summers, and higher flood risk. The cause is excess carbon dioxide in the atmosphere. Forests can play an important role in removing carbon dioxide from the air, as they transform it into tree trunks, roots, and leaves.

Much of the Hoosier National Forest has been accumulating carbon for more than 80 years. Since forest activists convinced the U.S. Forest Service to dramatically reduce the amount of timber harvesting in 1990, the Forest Service estimates the amount of carbon stored in the Hoosier has increased more than 40%.

Trees are 20 times as effective as grasses at carbon storage. About 10% of the carbon dioxide emitted in the U.S. is absorbed and stored in the nation’s trees. Allowing forests to mature allows them to absorb and store more carbon dioxide. When trees are harvested, some of the carbon remains locked away in the form of wood products such as lumber in houses. However, the process of timbering releases about 10-25% of the carbon from a stand back to the atmosphere. The Forest Service's plan for logging hundreds of nearly 10,000 acres of mature forest in the Hoosier National Forest will release much of its long-stored carbon.

Those favoring harvest will correctly point out that younger plants grow faster than older plants, so they remove carbon from the air at a faster rate. Stands of trees that are 30-70 years old are especially efficient carbon-storing machines. This is why planting trees in a non-forested area is good for reducing climate change in the long run. 

However, this doesn’t mean that cutting mature forests is good for climate change.  While maturing hardwood forests slow their net rate of absorption, the age at which they stop altogether is currently unknown. Earlier estimates cited by the Forest Service are giving way as more recent studies of old growth northern forests indicate they might continue to absorb additional carbon for hundreds of years.

Somewhat less than half of the stored carbon in a forest is above ground. The rest remains important but unseen such as roots, mycorrhizal fungal biomass, and organic litter in the soil. Not much is known about what happens below the ground after a harvest, such as how fast roots decay or how fast carbon is released from the soil. Most theoretical carbon analyses for forests only take the top half into account and we don’t yet understand the complete picture of how carbon cycles into and out of forests.

Large-scale cutting opens the forest floor to sunlight, warming it, and accelerating the release of carbon dioxide that is stored in organic material in the soil. The Forest Service’s own research in New Hampshire, albeit in a different forest type, concluded that for the first 15 years after harvest, release of carbon from the soil was almost equal to the new carbon stored in the young trees. It would take decades more before the fast-growing young trees make up for the amount of carbon that was released during the harvest. To make matters worse, the Forest Service plans to repeatedly burn about 32,000 acres of forest, accelerating the carbon loss from the soil. No detailed modeling or even rough estimates of the carbon dioxide that will be released have been attempted.

In the short run, harvesting releases carbon, with any net gain of carbon storage many decades into the future. Most scientists stress that it is critical to reduce carbon emissions immediately, over the next 15 years or so, if we are to avoid runaway climate effects. The Forest Service should leave the trees alone; they are doing us a favor.

Dex Conaway is the state forest director at the Indiana Forest Alliance. Tom Zeller is a long-time forest activist.