Bark beetle research shows future evolution of Utah forests
Dan Ott, right, and Kara Purser study spruce trees in the Uinta Mountains on June 18, 2014.
Dan Ott takes measurements with a gas chromatograph to extract chemical samples from a spruce tree on June 18, 2014.
Dan Ott prepares to measure spruce tree terpenoids while in the field at the Uinta Mountains on June 18, 2014.
Dan Ott takes field notes at his study site in the Uinta Mountains on June 18, 2014.
Dan Ott prepares to sling a line over a high spruce at his study site in the Uinta Mountains on June 18, 2014.
EDITOR’S NOTE – This is the first in a three-part series.
June marks the beginning of bark beetle season, when adult bugs emerge from the dead spruce and pine that sheltered them over the winter. Looking for fresh trees where they can mate and raise their brood, the beetles fly from tree to tree, emitting attractant pheromones to get more bugs to join them in a mass attack that wears down a tree’s defenses, or repellent pheromones letting other bugs know there’s no room left.
June also happens to be the time bark beetle scientists emerge from their offices and go into the field, gathering more data to add to an ever-growing body of knowledge about the small insects.
Dan Ott, a PhD student from Oregon State University, set out to the Uinta Mountains after an unseasonable snowstorm on June 18. It was his fifth week in the field, and a blanket of snow covered his study site by morning, which turned to a soggy puddle by afternoon. At least the sun shone bright in a clear blue sky. His studies often keep him out well after midnight.
Mountain pine beetles in the Uintas have wiped out nearly all the lodgepole pine in the region, and now the spruce beetles have started to pick up steam. For some reason, however, blue spruce are either less appetizing to bark beetles or are better at fighting them off than their relative species, Engelmann spruce. In some areas, beetles will wipe out all the Engelmann but only hit 10-20 percent of the blues, according to one researcher’s findings. Ott spent the season taking samples and monitoring trees. He’ll use the data he collects to figure out what it is about blue spruce physiology that allows them to persist.
“The beetles, they’re native, and they’ve kind of been evolving together with the trees over time,” he said. “So in outbreaks, the beetles kill most of the trees, but a few survive. Nobody’s actually sure which trees are reproducing on the landscape, but the trees do evolve over time.”
Bark beetles outbreaks have been munching on our forests for eons, long before humans arrived in the West. Occasional beetle outbreaks are normal, but what makes the current epidemic unusual is its scale. It has wiped out over 46 million acres in the U.S., the largest attack ever seen.
After a new forest grows and matures, the beetles will be back. A warming climate has both increased the pests’ range and sped up their cycles. Climate change also means drier conditions in the West, which make trees more vulnerable to attack. Understanding the evolutionary relationship between bugs and their host trees may be the key to understanding future landscape vulnerability. It can also help forest planners better manage the landscape once they have a sense of what’s coming.
It’s that interplay between human populations and the earth’s natural systems that interests Ott, and keeps him cheerfully trudging along in the field under less than ideal conditions.
“Going forward into the future, we’re going to have a bigger population, more pollution and our natural systems are going to become ever-more important for clean air and clean water,” he said. “I guess that’s good enough reason.”
He has curly brown hair and frequently switches out his neon-lens retro-style-Ray-Ban-sunglasses with square metal-frame eyeglasses. There’s a mountain bike in the back of Ott’s white Forest Service truck, and the tailgate doubles as his field lab.
No one’s quite sure why spruce beetles seem to prefer Engelmann species over blue spruce. It could be the thickness of their bark, how they respond to drought or where they grow. Among the many tree things Ott is analyzing in his spruce trees are the chemicals they produce, called terpenoids.
“Some of these chemicals are toxic to the beetles, others the beetles use to get into tree to create pheromone plumes to attract more beetles, or to tell other beetles to go away,” Ott said.
Finding a beetle ‘no vacancy’ sign
It’s those pheromones that interest Steve Munson, an entomologist at the U.S. Forest Service Forest Health Protection field station in Ogden. He spent part of the field season putting up spruce beetle traps baited with different pheromones in an attempt to figure out which one keeps insects away. Once he isolates that specific pheromone, foresters can use it as a repellent.
“We continue to work on repellents because, obviously, we’d like to get away from insecticides,” Munson said. “The problems with repellents is, these beetles usually have one generation per year, so you have a very narrow window to test it.”
Munson leads forest pest research for the region including Utah, Nevada and chunks of southern Idaho and western Wyoming. If you’re reading a bark beetle study, chances are Munson’s name is on it somewhere. While he’s the scientific equivalent of a celebrity among entomologists, Munson is affable and engaging. He came to Utah from the Midwest in the mid-’80s, and although most U.S. Forest Service promotions involve a lot of moving, Munson liked Ogden so much he never left.
He said it took around 10 years to isolate verbenone, the particular pheromone that mountain pine beetles use as a “no vacancy” sign after tree attacks. While it hasn’t been the forest salvation that some headlines touted, verbenone-based repellents helped protect high-value pines from beetle attacks at campsites, trailheads and ski areas. They’re hand-stapled to trees in plastic pouches at the beginning of beetle flight season.
“The problem with the pouches is they’re not biodegradable, so we have to go back and remove them,” Munson said.
Last year he finished incorporating verbenone with a wax-based matrix called “specialized pheromone & lure application technology,” or SPLAT, to make a repellent elegantly called “SPLAT-Verb.”
Unlike plastic pouches, the material is biologically inert. It’s hardly visible on the tree. Most importantly, it crumbles off, biodegrades and can save the U.S. Forest Service staff a lot of humanpower. With a dwindling budget that’s being diverted to fire fighting more and more each season, anything that cuts costs goes a long way.
The bug giving Munson the most trouble now is the spruce beetle. The mountain pine beetle has killed nearly all the mature pines in the West and starved itself out, but the spruce beetle is just starting to pick up speed. In Utah, Munson estimates the insects have wiped out around 50 to 60 percent of mature spruce so far, and he expects them to take it all.
“There are still trees left on our landscape that were impacted by the mountain pine beetle, but with the spruce beetle, it really hammers them,” he said. “You’d be hard-pressed to find a tree over 10 inches.”
Scientists haven’t yet been able to develop a repellent like SPLAT Verb for the rising spruce epidemic. Different bugs mean different chemical processes.
“There are many different pheromones and combinations of pheromones that we have to look at, so it just takes a while to come up with a repellent,” Munson said, “but we’re working on it.”
In the meantime, for spruce, the only option is to dose trees with hydraulic sprayers mounted on the back of trucks or trailers, spraying insecticide from hoses.
The mountain pine beetle has received a lot more attention from scientists and the media because they attack more tree species and a larger landscape than spruce beetles. But according to Munson, the spruce epidemic is concerning because it takes much longer for a spruce forest to regenerate compared to pine.
“We’re going back into those areas to replant spruce,” he said. “Areas where we can’t replant them because it’s too steep, it’ll take probably centuries to get a spruce forest back.”
Forest future in a warming climate
Forests move at their own pace, often beyond what’s observable in a human lifetime. Around 20,000 years ago, the massive Laurentide Ice Sheet covering most of North America began to slowly retreat as the last Ice Age ended. As the climate warmed, coniferous trees like pine and spruce began spreading through new territory, and so, too, did bark beetles.
According to Barbara Bentz, a U.S. Forest Service researcher based in Logan, the current epidemic has taken bark beetles to higher elevations and colder latitudes than previously observed, but it’s all a continuation of that process.
“It’s actually just an ongoing range extension over past the 8,000 years, as the beetles have followed host trees into Alberta and British Columbia,” Bentz said. “Recent climatic changes have sped up that process … not only is it moving north, it’s become more active in some high elevations forests in New Mexico.”
Bentz has an easy confidence, and at a recent mountain climate researchers’ conference, she was called the “go-to research scientist” and “leader in the community” for bark beetle research. Her work largely focuses on understanding the responses and adaptations of bark beetles and the role of temperature in outbreaks.
Bark beetles complete a lifecycle, from egg to egg-laying adult, once every one to two years. Like all insects, warmer temperatures mean bark beetles can speed up those cycles.To figure out what our ongoing warmer trend will mean for future bark beetle populations, she developed a model that matches up what scientists know about insect life cycles and compared it to future temperature predictions.
“At the highest elevations right now, it typically takes two years just to get one generation because it’s so cool there, it’s not very advantageous for population growth,” Bentz said.
Lower elevations where it’s generally warmer sometimes see beetles completing a full cycle in a year, unless there’s a cold snap to curb their development.
Using a similar emissions scenario and warming trend that’s been observed in the last 7-8 years, however, Bentz’s model suggests a climate that can successfully incubate more beetles than before. At higher elevations, more insects will be able to complete a single generations in one year instead of two. Things could get even worse. If humans don’t curb their own population and fossil fuel use, warming temperatures in the future could mean bugs in lower elevations complete an unprecedented two generations per year.
“That assumes an emission scenario that is not so friendly, where humans are really messing things up,” Bentz said.
These potential population explosions could be a huge problem for our forests. As with the current epidemics, when insect numbers build, they’re able to go after a lot more trees. And when thousands of beetles attack, even healthy, young trees are likely to succumb. Unless, of course, the trees move where it’s colder and less friendly to beetle growth.
The next step, Bentz said, is to compare her findings to research on how trees will also respond to warming. Using that global perspective, foresters can better understand future vulnerabilities in the landscape.
“The trees are probably going to move, they won’t be in the lower elevations,” she said, “but there’s only so far they can move … there’s going to be a point where there’s no place left for the trees to go.”
Bentz found an interesting outlier during the summer. Like the blue spruce, a pine species could be resisting mountain pine beetle attacks, regardless of elevation — the Great Basin bristlecone pine, pinus longaeva, which thrives in the arid southwest. It’s also known as one of the longest-living organisms on Earth.
“That’s based on one year of study, just to clarify,” she said, “but I think it’s pretty important.”
Like Ott, she collected samples and plans on analyzing the tree’s physiology to figure out why, and said it could be because of any number of things — maybe it’s their ecological adaptations or maybe it’s the terpenoids the trees produce. Whatever it is, it seems the Great Basin bristlecones have seen their share of beetle outbreaks come and go. Known trees of their species have pushed lifetimes of 5,000 years.
Giving evolution a chance
Diana Six, a professor of forest entomology and pathology at the University of Montana, said it’s important to consider the evolutionary histories of trees and beetles in current planning and management decisions, to ensure we have healthy forests that will adapt to future conditions. Both trees and beetles are genetically diverse, and the current epidemic might be sorting out the trees best adapted to climate change.
“The beetles are taking out trees adapted to past conditions that aren’t doing well, and they’re leaving behind some that are better-adapted, but didn’t grow as well 50 years ago,” she said.
If you understand evolution, Six said, a selection event that wipes out a large number of individuals in a population, selectively killing some but leaving others, is what shifts the genetic composition of the next generation.
It may be what helped both blue spruce and Great Basin bristlecones develop their resistance to beetles while other species remained vulnerable.
“People don’t think on a forest timescale,” she said. “Beetle and trees have been interacting for a very long time, and in some ways, beetles probably help make trees healthier.”
