Spruce beetles’ expansion into Denali poses questions about future changes in the forest

While more summer warmth has been linked to beetle infestations in Southcentral Alaska, less winter cold may be at play in and around Denali

Along with the tourist crowds that are flocking to Denali National Park and Preserve is another arrival: Masses of beetles have burrowed into the park’s spruce trees and begun killing them off.

The aggressive infestation that took hold in the Matanuska-Susitna Borough north of Anchorage in 2016 has now spread north, covering hillsides in the communities outside the park with rust-red dead trees and reaching into park boundaries.

The ferocity and northward spread of that “epic” Mat-Su infestation surprised Glen Holt, a forester with the University of Alaska Fairbanks’ Cooperative Extension Service.

“I didn’t really see this coming. I thought we’d be good for another 50 years because of the previous outbreak in the ’80s and ’90s,” he said, referring to a massive infestation concentrated on the Kenai Peninsula that killed trees over about 3 million acres, according to the U.S. Forest Service.

Spruce beetles are native to Alaska, and they can be found throughout the spruce, birch and aspen region known as the boreal forest, albeit in small numbers in the very far north. They bore through the bark of spruce trees, mostly white spruce, to eat and breed in the soft tissue underneath. Since that soft tissue is critical to the trees’ survival, the presence of beetles inevitably kills trees.

But while the beetles are considered to play a role in the boreal forest lifecycle, outbreaks in the modern era have been different than those in the past.

The 1990s epidemic killed trees in 40% more territory than was affected in all the Alaska infestations over the prior 70 years combined, according to scientists from the Forest Service, U.S. Fish and Wildlife Service and Alaska Department of Natural Resources. The infestation spreading into the Denali area is of a scope rarely observed that far north in the past, according to park scientists.

In the more populated and developed Southcentral Alaska regions where beetles have taken hold, residents regularly cut down infested trees on their properties and take precautions to prevent new infestations, including applications of insecticide. The state Division of Forestry and other agencies and organizations have offered numerous public-education opportunities to help residents avoid accumulations of flammable, beetle-killed timber and other pitfalls.

In Denali, where the national park mission of preserving nature prevails, there is a different approach: Managers are not interfering with the beetles’ march northward.

“The Park Service is not really in the business of messing with the native processes. In fact you can say that’s what we’re trying to preserve,” said Sarah Stehn, a park fire ecologist.

Letting nature, and the beetles, take their course

Rather than try to hold back the wave, Denali scientists and managers intend to watch closely as it spreads over the next several years. The park has established a multitude of study plots throughout the park that will be monitored, and comparisons will be made with what has happened farther south, said Carl Roland, a Denali plant ecologist.

“We want to see not just the pattern of mortality but also how does the forest respond after the wave has broken? In the long term, decades out, what comes back? Is the nature of the forest that comes back the same or different?” Roland said.

Another question is how far north the wave will reach. The nature of the forest on the north side of the Alaska Range, which bisects Denali National Park, could moderate the spread, Roland said. Trees on the south side of the range grow bigger and faster and therefore can harbor more beetles than the slower-growing northern trees, he said.

As to whether the northward beetle spread is a good or bad thing, park scientists are, to some degree, withholding judgment.

“Whether it’s objectively a problem depends on whether you’re a spruce beetle or not, I suppose,” Roland said.

It can also depend on what kind of boreal animal you are. For squirrels, which depend on spruce for their food, the infestations could mean trouble. For one type of beetle-eating bird, the American three-toed woodpecker, the infestations could mean a rich bounty. The park scientists plan to monitor squirrels and woodpeckers to see how each species fares over the coming years, said Roland.

For people visiting the park and those living in the communities near it, the sweep of beetle infestations and dead trees can be concerning, Roland and Stehn said. Park rangers are gearing up to answer more visitor questions over the next few years as the infestation progresses.

“You know, people who live in the forest are pretty affected when it dies around them,” Roland said.

A more tangible concern for park managers are what Roland called “hazard trees” that are at risk of toppling over on heavily used areas like campsites. So far, at least one of those trees has been cut down, said Sharon Stiteler, the park’s public information officer.

Another looming issue is wildfire risk, particularly in the heavily used front country, where there are big crowds and important structures. Denali had been working on improving fire safety there, ensuring that there are routes in and out for visitors and firefighters if the need arises, and the beetles’ arrival does not change that, Stehn said.

Park officials are taking lessons from the high-profile fires that burned in beetle-infested areas in past years on the Kenai Peninsula and in the Matanuska-Susitna Borough, she said.

Warmer summers or less-cold winters?

Exactly why this latest infestation is spreading, not only north to Denali but also south in another wave on the peninsula, is a subject of continued study.

On the peninsula and elsewhere in Southcentral Alaska, past years’ explosions of spruce beetles have been linked to warming summers. With higher summer temperatures, beetles burrowing into trees were able to shorten their life cycles from two years to one, thus doubling their reproductive ability, according to research led by Ed Berg, a now-retired U.S. Fish and Wildlife Service ecologist who witnessed the 1990s infestation at close range from his base in the Kenai National Wildlife Refuge.

But in Denali and elsewhere in Interior Alaska, seasons are more extreme. The summer heat that seems extraordinary in the coastal Kenai Peninsula is common in the Interior regions of the state. Rather than summer changes, it appears that changes in winter are the key factor in the beetle expansion. Winters are no longer cold enough to kill off nesting larvae; long-term records at Denali’s headquarters show that frequency of ultra-cold winter days has diminished notably over past decades, a sign of climate change. There has been no minus-40-degree reading there since 2012, though such readings were once considered normal.

Nonetheless, Roland said, the beetles’ northward creep in recent years over the broad, higher-elevation area known as Broad Pass was a bit of a surprise to him.

“I basically didn’t expect them to really come over Broad Pass so much. I thought it would slow down,” he said. “I thought it would be too cool up there in the summer, so I was wrong about that.”

Jason Moan, the forest health program manager for the Alaska Division of Forestry, has tracked the beetles for several years. He noted that their relationship to temperature and climate change is multifaceted, complex and sometimes hyper-localized.

“Even in a single tree, you can have some that are developing in two years and some that are developing in one year,” he said. Differences can depend on which side of the tree the beetles have settled, he said.

Snow levels can play a role, with snow abundance insulating trees, holding in enough warmth to let beetles survive the winters, and snow scarcity leaving tree trunks exposed to cold air, potentially killing off overwintering beetles, he said. Availability of water can have an effect too, with drought-stricken trees struggling more, he said.

In general, the farther north habitats have enough cold winter temperatures to keep beetle populations low, Moan said. But the characteristics of the beetles now in Denali National Park, including their reproductive cycles and winter durability, have yet to be determined, he said.

Outside of park boundaries, natural resource managers, experts and property owners have been taking aggressive steps to respond to the latest spread.

A key goal is protection from wildfires that can sweep in when infested trees are in their most flammable state – dead but with rust-red needles and resin still intact.

Human interventions encouraged, but they have practical limits

For decades, the Division of Forestry and other agencies have been urging property owners to establish precautionary “defensible space” by removing infested trees that are close to homes and buildings.

“The time to do that is not when you see a large cloud of smoke. The time to do that is before then,” Holt, the UAF Extension Service forester, said in a public workshop held in Palmer on July 19.

One state program that could help address the beetle kill attempt is the pending carbon-credit system to be created under a newly signed bill passed by the Alaska Legislature. The bill, a big priority for Gov. Mike Dunleavy, authorizes a system of carbon-trading credits for preservation of Alaska forest tracts. Through that program, there could be incentives to log infested areas and clear the way for healthier and potentially less burn-prone trees, some bill supporters said.

John Boyle, commissioner of the Department of Natural Resources, made that specific pitch last spring. Replacing dying or dead trees with new trees will result in more carbon absorption by the forests, Boyle said in a brief interview in the Capitol hallway immediately after the Alaska Senate approved the bill.

The beetles play a role in the forest ecosystem, but “to the extent that we can manage around that and keep it from laying waste to hundreds of thousands of additional acres of land, we’ll certainly take a hard look at that and see what we can do to be more proactive on that front,” Boyle said.

Outside of the carbon-credit program, which has yet to be set up, the department’s Division of Forestry is planning a series of timber sales that would sell off beetle-killed spruce wood from over 1,271 acres in the Matanuska-Susitna Borough. Key purposes of the planned sales, to run through 2026, include efforts to salvage economic benefits from the dead spruce “before it loses substantial value” and to reduce wildfire risks to nearby communities, according to the division analysis issued on July 14. It is possible that no one will submit competitive bids, leaving the option of selling directly, without any bidding, to any future interested parties, the division said in its public notice of the sales.

Even in Denali, where the strategy is heavy on science and research and extremely light on human action, there is evidence of past salvage of beetle-killed trees. A cabin built by in the 1920s by the park’s first superintendent, Harry Karstens, which has since been relocated to the park headquarters area, was constructed from infested wood, as is evidenced by the curling burrows dug by beetles beneath the bark a century ago.

No matter how hard and creatively people work, however, the beetles will continue to sweep through boreal Alaska, Holt said. Though Alaskans can clean up the fringes by removing some infested trees, there will be changes in the vast forest that human intervention cannot stop, he said.

“There’s a lot of spruce trees that nobody’s ever going to get to,” he said.

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