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Beetle-kill zones surprisingly rich in biodiversity

The drive over Wolf Creek Pass, scarred by the spruce beetle outbreak, can elicit strong emotions in the nature lover. Several logging sales may be on the way, but new research suggests ravaged trees can create an ecologically vital habitat worth saving.

Since 1996, nearly 588,000 acres in the Rio Grande National Forest and 120,000 acres in the San Juan National Forest have fallen prey to the spruce beetle scourge. In its wake, the outbreak has left many questions about how to best approach reforestation.

In February, Forest Service officials announced plans for a small salvage sale of about 100 acres of dead spruce near Wolf Creek Pass, which could expand to another 800 acres off of Wolf Creek and Falls Creek roads.

The federal agency will also consider a 900-acre sale in the Dolores Ranger District, in the Taylor and Stoner Mesa areas, and evaluate the best sites for salvage sales on forest land north of U.S. Highway 160 between the Piedra River and Vallecito Lake.

The Forest Service has long maintained such timber sales benefit the health of the ecosystem as it transitions from an old-growth to new-growth forest, but research from the University of Montana, as well as several conservation groups, challenges that idea.

A ‘bonanza’ for wildlife

“These areas where beetles killed trees is a really important habitat, ecologically,” said Chad Hanson, director of the John Muir Project, a nonprofit group opposed to salvage logging.

“It sounds counterintuitive, but for wildlife species, those areas are a bonanza,” he said. “Science is telling us these habitats are every bit as important as the forest before the kill-off.”

An infestation begins when a female spruce beetle finds a weak tree and signals to more beetles to attack. The insects chew through the bark and then enter a layer of the tree where they lay eggs in a network of tunnels. The eggs hatch, the beetles grow up and fly away. Before leaving, the mature beetles spread a special fungus in the center of the tree that ultimately kills it.

But it’s what happens after that Hanson says is so important for the ecosystem.

After the beetle moves on, woodpeckers feed on the larvae left behind, which creates nest cavities in dead trees for other species – such as bluebirds, chickadees and even squirrels – who are unable to make the safe havens themselves.

Then come the wildflowers, which thrive on the exposed understory of the forest, typically covered in shade. Flies and other insects arrive to feed on the flowers, and in turn bring birds, bats and other small mammals, which attract larger predators.

“What you end up with is a very rich and biodiverse ecosystem,” Hanson said.

Clark University associate professor Dominik Kulakowski agreed. He said the result, a “snag forest,” is a favorable habitat for many invertebrates and vertebrates because of the creation of canopy gaps and enhanced growth of understory plants.

“Outbreaks create snags that may be used by various birds and mammals, including woodpeckers, owls, hawks, wrens, warblers, bats, squirrels, American marten and lynx,” Kulakowski said.

By removing the trees, you remove this process, both Hanson and Kulakowski said.

Drought, temperatures drive outbreak

In her 2014 report for the University of Montana, entomologist Diana Six said the long-standing method of thinning and salvaging does little to reduce to risk of beetles spreading and forest fires.

Instead, underlying conditions – warmer temperatures and drought – are the main drivers of those threats by allowing longer seasons for beetles to thrive and weakening trees to fight infestation. What has resulted is the largest outbreak of beetle kill recorded in human history.

“During an outbreak, these treatments are doomed to failure,” Six told The Durango Herald. “If warm temperatures and drought are driving an outbreak, by cutting trees you can’t reduce the outbreak because it doesn’t change the conditions.”

Six said it’s human nature to want to do something to address the problem, so methods like logging gain traction.

“The forests look devastated, and our gut feeling is ‘My God this has been terrible,’” she said. “But if we step back and look at forest processes, sometimes just standing back and not doing anything might be the best approach.”

Protecting the understory

Gretchen Fitzgerald, a forester with the San Juan National Forest, said the agency takes care to protect understory growth and do as little damage as possible, but reforestation is complicated.

She estimated only 50 percent of trees on the 100-acre site on Wolf Creek will actually be logged, and even that area is a small sliver of the entire affected forest.

“There’s tens of thousands of acres of dead trees up there we are not touching,” Fitzgerald said. “We’re just accessing areas close to roads. It’s a place we can get to without too much environmental damage.”

The Forest Service acknowledges timber sales do little to prevent the spread of beetle kill, but they can help clear out some areas prone to forest fires.

Beetle kill is a natural process, Fitzgerald said, and though the outbreak is intensified by climate change, it’s important to take the long view.

“It’s converting from an old forest to a young forest,” she said. “And just because the overstory has died doesn’t mean you’ve lost biodiversity. It’s not like it’s a dead forest.”

Reports last summer estimated that varying species of beetles despoiled 46 million of the country’s 850 million acres of forest land. Since 2001, more than 50 bills have been introduced to promote timber sales to combat the outbreak.


Map of spruce beetle activity (PDF)

Sep 19, 2018
Logging returns to the San Juan Mountains

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