Pine Beetle Invasion Is Over, For Now

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For nearly 20 years, the mountain pine beetle infestation slowing ate its way through the Black Hills.

More than 400,000 acres of private and public land were affected. The infestation cost millions of dollars and changed the look of the forest. Some thought it would never end, but it finally did. What has been learned?

In the late 90s, foresters and loggers began to notice more and more bug-killed trees in the Black Hills. The problem was particularly bad in the woods south of Sturgis, and then in the central Hills.  

“Twenty years ago when the thing first started, we had a very different forest. I mean, it was very dense
overall, full of much larger trees. Basically we had a forest full of very suitable hosts and food for the
beetles,” said Kurt Allen, entomologist with the Forest Service. 

Pine beetles are native to the western forests and they had been appearing from time to time for over a
century. But this time it was different.  

The beetle infestation grew.  At the height of it, about ten years ago, more than a third of the acreage of the Black Hills National Forest had been affected.  

“It’s actually kind of amazing, if you’ve been around for the last 20 years and seen just the changes that occurred,” Allen said. 

In some places, entire ridges that had been thick with trees were stripped.

In response, the Forest Service undertook an aggressive thinning program, especially in places close to the infested areas.  

Thinning deprives the insects of suitable hosts, and it slowed the advance of the infestation. But it was a long fight, and some critics began to wonder just how many trees would have to be cut down to stop it. 

But then, about four years ago, foresters began to notice a slowdown. 

Forest Service Entomologist Kurt Allen has spent half of his career fighting pine beetles. And even he is now surprised that the infestation finally seems to have ended. 

“You go out there now and it’s even had to find the buggers out there in the landscape,” Allen said. 

City and State foresters say much the same thing.  

“As far as pine beetle there’s very little activity in town. Like I said, occasionally one or maybe two a year, tops, but few and far between,” said Andy Bernard, with Rapid City. 

“But in the Park they’re pretty normal. It’s what we would call endemic levels where they’re only affecting weakened and stressed trees. Healthy trees are going to be just fine,” said James Canfield, forester at Custer State Park. 

To this day, entomologists and foresters aren’t entirely sure what started the infestation, or what stopped it. But they know pine beetle invasions are part of the long, 10,000 year history of these forests. The last big infestation began around 1890. It probably killed about as many trees.

“The one we just went through probably covered a greater area,” said Allen.

And today, just as they did a century ago, the trees are returning to replace the ones brought down by the beetle. 

“There is an incredible crop in most places of small pine trees growing up in their stead,” said Allen. 

Scientists now know that pine beetle invasions are part of the natural cycles that maintain a balance in
woods. But an infestation can be disturbing while it’s happening, and many who love these woods are glad it’s over. There is, however, a cautionary tale in the story of the bug.

“It will return again at some point in the future,” said Allen. 

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