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Scientists say insects and diseases are reducing forests' carbon trapping potential

The Florida Panhandle is a heavily forested region. The hurricane tore down millions of trees.
Sam Tarling for NPR
Cedar trees in the Tannourine Cedars Forest Nature Reserve, in Tannourine.

Insects can be part of the natural rhythm of a forest, says Leigh Greenwood, Forest Health program director with the Nature Conservancy.

But they can also damage those same forests.

“When we see extreme changes like from non-native insects and diseases, or from insects and diseases that are native but are being exacerbated really severely by the effects of climate change or poor land use patterns over time, then we see severe carbon impacts,” Greenwood said.

Insects and diseases that injure or kill trees are reducing American forests' carbon sequestration capacity by 50 million tons of carbon dioxide a year. That’s the equivalent to the emissions of more than 10 million cars on the road.

These are the findings of a recent study published in the journal Frontiers in Forests and Global Change. The study was authored in part by the Forest Service and the Nature Conservancy.

“When a tree is being stressed out by an insect or disease, whether that's because it’s getting its leaves nibbled on or there’s a fungus growing in its bark, some sort of a disturbance that makes the tree struggle," Greenwood said. "The tree simply can’t put on as much wood, so it can’t trap as much carbon within itself as part of natural growth."

Because trees can capture and store carbon, forests play a big role in tackling climate change.

To study lost carbon potential, scientists compared forest plots damaged by insects and diseases with healthy plots over time. The insect plots were much worse off than the disease plots: Those plots sequestered on average 69% and 28% less carbon, respectively, than their undisturbed counterparts.

And Montana isn't immune to forest pests.

“The study really reinforces the importance of healthy forests and the role that they play for lots of objectives: wildlife and water quality, timber and aesthetics, and carbon sequestration as well," said Amy Gannon, a forest entomologist with the state Department of Natural Resources and Conservation.

"Whatever we can do to maintain the health and vigor of those forests is going to really help many of those objectives, and it’s going to be worthwhile in the long run,” she said.

Greenwood says there are ways states can bring forests back into balance, including forest management policies that encourage biodiversity. In the Interior West this can include prescribed burns and thinning when trees get too dense.

“Almost all of the insects and diseases that we work with are specific to one or a couple types of trees," Greenwood said. "So if you have a big variety of trees you’re much less likely to have a catastrophe hit you."

Greenwood also suggests not moving firewood long distances. It can carry insects and diseases.

“Moving firewood only very short distances and gathering it on site for camping or for when you go hunting or around your cabin instead of moving it from out of state or even across big states, that’s actually an everyday step anyone can take to help prevent the movement of insects and diseases,” she said.

Greenwood says it’s going to take a lot of actions all at once to meet carbon reduction goals — including healing our forests.

Olivia Weitz covers Bozeman and surrounding communities in Southwest Montana for Yellowstone Public Radio. She has reported for Northwest News Network and Boise State Public Radio and previously worked at a daily print newspaper. She is a graduate of the University of Puget Sound and the Transom Story Workshop.