Bark beetles turn forest into carbon source

Dec 6, 2013

Pine and spruce beetles have killed millions of trees across Wyoming and the West. To many, the dying forests are visually unattractive. But there’s a bigger issue. Researchers in the Medicine Bow National Forest are finding that beetle kill has had a major impact on how the forest processes carbon dioxide. Wyoming Public radio’s Willow Belden reports.

WILLOW BELDEN: It’s quite a trek to get out to the Glacier Lakes Ecosystem Experiments Site, in the Snowy Range. A team of researchers drives a giant snow cat part of the way, then they switch to cross country skis for the final stretch through the woods. The research station itself is tucked discretely among the trees. There’s a tall metal tower, equipped with fancy instruments, and a small building where computers record the data that’s collected.

Engineer John Frank built the tower, and he comes up every week to check the equipment. Today, the wind is blowing at more than 40 miles an hour as he climbs to the top of the tower.

BELDEN: A little breezy up there?

JOHN FRANK: Oh my. That was terrible.

BELDEN: Frank says one of the key things they’re measuring at this site is how much carbon dioxide the forest takes in, and how much is released back into the atmosphere. Normally, forests absorb more carbon than they release. But Frank says beetle kill has changed that. 

JOHN FRANK: This forest went from being a carbon sink … to being actually a carbon source.

BELDEN: In other words, the forest now gives off more CO2 than it takes in. This is one of just a few locations in the world where scientists are documenting how beetle kill affects the carbon cycle. But Frank says his team was not particularly surprised by what they’ve found.

FRANK: We all knew that to have a good carbon sink going you needed to have a good healthy, living forest.

BELDEN: And the Medicine Bow National Forest is not a healthy, living forest. Eighty percent of the trees are now dead, largely as a result of beetle kill.

FRANK: It looks bad. It looks bad right now. And our sensors are telling us that effectively it is bad, in terms of being a carbon source. That’s not a good thing.

BELDEN:  Not a good thing, because extra carbon dioxide in the atmosphere contributes to climate change.

But Steven Running, an ecologist at the University of Montana, says this is not the first time this has happened. Forests become carbon sources often when there’s a disturbance like a wildfire, or logging. Still, he says, this beetle kill epidemic is a little unusual.

RUNNING: I’ve had entomologists tell me it’s the single biggest forest mortality event in the world. … And so this is unprecedented in overall area.

BELDEN: Then again, not all forests are created equal, and Running says a major die-off in forests here in the Rockies is not especially disturbing, on a global level.

RUNNING: Compared to the tropics, our arid temperate forests of the west aren’t very big sinks when they are a sink. They’re not very big sources when they are a source. We really aren’t a big player in the terrestrial carbon cycle.

BELDEN: And regardless, it’s pretty likely that the trend will eventually reverse itself.

BILL MASSMAN: Eventually we’ll run out of trees, at least up here.

BELDEN: Bill Massman is the lead scientist at the Medicine Bow research site.

MASSMAN: And so the beetles, at some point, will just simply run out of food and the population will probably crash.

BELDEN: Massman says once the beetles die out, new trees will most likely grow, and the forest should go back to being a carbon sink. But nobody knows how long that will take.

MASSMAN: This is a very harsh environment. Things grow very slowly up here. So I’m not sure that it’ll be five years, ten years, or fifty years.

BELDEN: In the meantime, as more trees die, the forest will likely absorb even less carbon dioxide. For Wyoming Public Radio, I’m Willow Belden.