When the next major outbreak of spruce budworm strikes the forests of the Northeast, millions of acres of trees will be at risk. Nearly 100 million metric tons of stored carbon will also be at risk of being released into the atmosphere when those trees die.
That realization got John Gunn thinking about the decisions landowners will soon be making about whether to salvage that timber after the outbreak hits or to leave the dead trees to decompose into the soil. Those decisions have significant implications for greenhouse-gas emissions, as well as for the ecology of the forest.
According to Gunn, a research assistant professor of forest management at the University of New Hampshire, if the trees are left in place to decompose, some of the carbon they had sequestered will eventually be absorbed into the soil, but much of it will be released to the atmosphere. If the trees are salvaged, some parts of the tree remain at the site to decompose, while most of it is hauled away. Depending on how the salvaged trees are used, some of the carbon may remain in the wood for many years. If it’s made into paper, then the carbon is released much sooner.
Using data from the U.S. Forest Service and its Forest Vegetation Simulator, Gunn simulated the greenhouse-gas emissions likely to result from a number of scenarios after spruce budworm kills the majority of spruce and fir trees in the region.
“Our general finding is that the decision to salvage dead trees leads to more carbon in the atmosphere for the next 10 to 20 years,” he said. “But after that time, you get to parity because of the new growth of trees and because there’s still carbon stored in solid wood products.”
From a total carbon emissions perspective, salvaging dead trees may be the better long-term decision even though leaving the trees to decompose is a better decision in the short-term. On the other hand, “climate scientists are telling us to do everything we can to reduce greenhouse-gas emissions over the next 20 years,” Gunn said. So you have to weigh what’s more important: the long-term potential emissions benefits or the short-term need to not send any more carbon to the atmosphere.”
His recommendation is to look for the middle ground, in part because carbon emissions aren’t the only consideration. Landowners must also factor in their need for a return on their investment, and ecological factors should also be assessed. “There are a lot of ecological reasons to leave that deadwood standing and leave that structure, because it’s an important component for biodiversity,” Gunn said.
He is now working with a team of computer scientists to evaluate this decision-making in a world where carbon has a value to society. “If we were to truly value carbon sequestered in the forest, it might nudge you toward decisions to let forests grow longer or leave the deadwood out there, assuming someone would pay you for it,” he said.