Spruce Bark Beetles and Climate Change

By Charles Wohlforth

All rights reserved

It was the biggest single insect kill of trees ever recorded in North America, southcentral Alaska’s 4 million acre spruce bark beetle plague, so you might think that finding out why it happened would be a scientific priority. But only one researcher looked deeply into the question, a soft-spoken forest ecologist with a bushy beard who wears flannel shirts and suspenders.

Ed Berg, working at the Kenai National Wildlife Refuge, had the skills and the curiosity to find the clues and fit them together with advanced statistical analysis. What he found turned out to be much bigger even than even the beetle kill.

Here are some of the clues:

* In the Mystery Hills, on the Refuge’s Fuller Lakes Trail, krummholz trees, those old, gnarled hemlocks that creep along the ground, shot up straight and tall as if suddenly cured of their rheumatism. After centuries of struggling for life at the edge of treeline, they’re young again, growing fast in ideal conditions. Treeline, the limit of these trees’ habitat, is way up yonder now, up where no trees have yet colonized.

* To the west, on the mostly flat, pond-pocked land near the Swanson River, kettle ponds are evaporating away, their shrinkage measured from old aerial photographs and the bathtub rings left by receding shores. Some have disappeared entirely, leaving a telltale concentric pattern of vegetation that is younger and younger toward the center, where the deepest water used to be.

* All over the region, inside the trees, rings record each year of growth, an accurate gauge of conditions in that area of forest. Counted and precisely measured by Berg and his assistants on a microscopic slide wired to a computer, and compiled by the thousands, they confirm that the 1990s beetle kill was the largest to hit the area in at least 250 years. Beetles have killed a lot of trees before--they come through regularly--but in the past cool, damp weather stopped them before they could so thoroughly wipe out so much forest.

The clues all fit a conclusion: the climate changed enough in this region--it has become hot enough and dry enough--to swing the ecological balance of power strongly in favor of spruce bark beetles and away from spruce trees. This huge beetle kill was a direct result of global warming. And it may have been a preview of how newly empowered insects could devour other Alaska forests as change advances.

Berg hasn’t yet published his findings in a peer-reviewed scientific journal, but experts in Alaska buy it. "It’s just difficult to account for in any other way," says Glenn Juday, a professor of Forest Ecology at the University of Alaska Fairbanks. Juday and his colleagues put enough stock in Berg’s work to include his conclusion in a Congressionally mandated report by the National Assessment Team of the U.S. Global Change Research Program.

Twenty years ago, experts such as Forest Service entomologist Ed Holsten didn’t believe this could happen. Alaska lost 2.5 million acres of spruce to bark beetles from 1920 to 1990. In the next 10 years, 4 million acres died, and much of that in an uncharacteristic way. Beetles normally attack only the largest spruces, but in some areas beetles took out almost every tree, large and small.

"We had entomologists coming up and just scratching their heads," Holsten says. "If you read the textbook, the spruce beetle is just not very aggressive."

Homer was supposed to be immune from spruce bark beetles. But in 1988, when Ed Berg left for Georgia to become an ecologist instead of a carpenter, it was already evident that the experts were wrong. Red, dying spruce trees were showing up around Kachemak Bay, where the maritime climate had been too cool and wet for bark beetles to do much damage in the past. Still, Berg himself didn’t see the significance of it.

His career followed an eccentric trajectory to bring him to his discovery. Caught up in the early 1960s Sputnik craze for the hard sciences, he first became a geophysicist, but quit short of completing a PhD thesis for ethical reasons. Studying in Madison, Wisconsin, he had joined the movement to oppose the Viet Nam War and came to believe his study of the earth’s crust could be perverted by the military. The Navy could use the knowledge to develop communications with nuclear-armed submarines. Berg switched to philosophy, got his first doctorate, and became a carpenter.

A philosopher, a skilled finish carpenter, a liberal war protester: Berg had a dream résumé to live among the big Sitka spruces on Homer’s East End Road, where he ended up in a community of like minded people in 1982. Free spirits inhabited these woods, building fanciful houses hidden down narrow, muddy roads. Berg’s neighbor liked to sing in the chapel of big trees outside her door. "I loved living in the forest," he says.

But in 1992, when Berg returned from Georgia with a PhD in botany, it was clear that his home was changing. "The beetles had really taken off at that point, and I could see a lot of my trees had beetles in them," Berg says. He decided not to spray, but it didn’t really matter; nothing could stop the insects at that point.

Each spring in the mid-90s when the beetles flew looking for new trees to infest they swarmed like a Biblical plague.

"I can remember them coming, kind of like an Alfred Hitchcock movie," Berg says. "They would be in your hair and your eyes, you’d have to brush them off. I’ve heard people saying they could see them in clouds, miles off, coming down the Anchor River Valley."

The beetles spend most of their lives inside a tree, eating a thin layer of inner bark called the phloem, which carries food produced in the needles down to the roots for storage. Eggs hatch during the summer and the larvae begin chewing away. The insects stay in the tree over the winter, the next summer, the following winter, and next spring make their brief flight to find a new tree in which to lay eggs.

If the new tree’s sap is flowing, it can flush the beetles out before they get started. Young trees, rich in sap, usually are immune. Most trees have good defenses in cool, damp weather. Even if one generation of beetles does well, the next can be knocked down by a cool spring. For the beetles to fly successfully, the outside air must be at least 60 degrees.

Best for the beetles, and worst for the trees, is when such a warm day comes early in the spring, when the ground is still frozen. At those times, with moisture evaporating fast from the needles but little dampness available to draw from the frozen roots, the trees have little defensive sap and beetles can have a field day.

Spruce bark beetle infestations have always come and gone, but never lasted more than a few years before a return to cool weather put a stop to them. Tree ring records show the weather has been that way for at least 400 years. But since 1987, southcentral Alaska has had an unbroken string of abnormally warm summers. Some summers in the 1990s were so warm beetles grew to maturity in one year instead of two, doubling the hit on the forest the next spring. So many beetles flew that young and old trees were overwhelmed in some places, leaving little living for regeneration. The plague didn’t slow until the beetles ate their way through all the available acreage.

The forest along East End Road died, among many. Some people chose to cut their trees rather than live with the fear of fire and blow downs, including the whole neighborhood where Berg lived. He decided to move into town, partly because of the loss of privacy and the chilly wind that constantly blew off the bay after the trees were gone.

The neighbor who sang from her porch, Mary Jane Shows, stayed and lives there still, although now the area looks like a perpetually messy construction site. During a recent storm, her husband, John Shows, heard a big tree crashing down every minute or so. So he’s glad he cut his trees. But he calls the area left around their home "Beirut."

Their trees and thousands of others went into a chipper and out to Homer Spit to be loaded on ships bound for Japan, there to become paper. When you look into the holds of those bulk carriers you get a sense of the scale of how many dead trees there are. These ships are far larger than the largest building on the Kenai Peninsula, but they are as simple as a bath tub toy--just a big boat with immense empty spaces to be filled. The chips gush into these spaces from a conveyor belt, a torrential waterfall of wood cascading down in a spray of sawdust. But even at this prodigious rate, it takes 12 hours to fill just one of the six holds. Ships come every few weeks. And in years of this loading, they’ve taken only a small nibble from all the dead trees.

Most trees will fall and rot in place before anyone harvests them. In Bear Cove, on the south side of Kachemak Bay, where the infestation hit early, many of the trees have already fallen. Now that land is impassable, like a giant’s game of pick-up sticks. Once you might have walked or skied through the forest; now it’s a no man’s land, probably for a generation. Berg recently visited a site near Point Possession where beetles came through heavily in 1958. It is good wildlife habitat, full of devil's clubs and other berries, but the downed trees continue to make tough going for people.

With a changing climate, it’s anyone’s guess what will happen next. The ecology of this part of Alaska has changed: spruce beetles won’t be limited by cool, wet springs anymore. With further warming, they may spread next into the coastal rainforest; infestations have arisen already around Haines and in Glacier Bay, drier pockets of that ecosystem. Canada’s Kluane National Park has them in forest that never had them before; Berg is training their scientists in his techniques so they can study them.

Or some other insect could make the next run. "With climate change in the northern latitudes, we might not be able to predict which insect will be the problem, but we know we will have increased insect activity," says entomologist Holsten.

He studies and records increased outbreaks of various bugs with odd names, creatures such as the larch sawfly. No one had seen one in Alaska before 1965, and now it has taken the needles off just about every larch in Interior Alaska for the last seven years. A mystery malady has killed half a million acres of valuable yellow cedar in southeast Alaska, too, possibly because climate change has reduced snow cover that protected roots from freezing.

Ecologist Juday sees much of Alaska becoming more like southern Alberta, with grasslands and parklike clearings of broadly spaced trees. It could look as it did during the ice ages, habitat for elk, bison and wild horses. "It would be kind of back to the future," he says.

But Juday admits that’s just a guess. The real lesson of climate change and the spruce bark beetle is that we have no idea what big things might happen. Ecosystems are still far beyond our understanding, Juday says.

"They have factors that we don’t even know about, like some bug that comes out of nowhere, that’s not a factor, then you warm it up a little bit, and it’s not a factor, then you warm it up a little bit more, and, boom, it is the only factor. And not only do we not know how that works, but we don’t even have a name for the bug yet."

When Beryl Myhill and her husband Howard bought their 11 acres off West Hill Road in Homer, there were no big trees around, nor any stumps or signs of a burn. That was in 1946. Over the years since then, she felt the climate warm in Homer--she saw how winters got milder--and she watched a forest grow up around her house. The tree line came to lie just uphill of her place.

A few years ago the beetles hit and all those big trees died, including her favorite, where her husband once strung a radio aerial, and her sons’ favorites, where they played as children. Howard died in 1997 and their five sons all grew up and moved away. Beryl cut the dead trees to keep them from falling on anyone. She felt sick, but she assumed God had made a decision.

"You know," she says, "there’s a cycle of life to everything. Those trees, they come up and they grow to maturity and they deteriorate and finally they die and the little ones grow up.

"Everyone says it’ll grow up again. Of course, I won’t be here to see it."