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Story by Emily Stifler | photo by Gregg Treinish
Cross Homestake Pass on I-90, or hike into Beehive Basin north of Big Sky, and you’ll see a predominance of dead trees, their needles a vivid coppery color. Mountain pine beetles, the cause of much of this mortality, are native to the Rocky Mountains, and are part of lodgepole pine forests’ natural life cycle. Historically, the beetles have also affected ponderosa, sugar, and western white pines, and two 20th century beetle epidemics killed whitebark pines. All of these species recovered.
Since 2000 however, scientists from Colorado to British Columbia have recorded a significant rise in beetlekilled whitebark pine, in subalpine ecosystems. While the percentage of forest death varies between ranges, this epidemic, combined with the invasive white pine blister rust, has caused unprecedented mortality.
“While, historically, climatic conditions in high elevation whitebark pine habitats have prevented sustained mountain pine beetle outbreaks, today anthropogenic global warming appears to be allowing outbreak populations to expand into these previously inhospitable areas,” according to a 2001 paper on by whitebark experts Jesse Logan and James Powell.
In 2009, the Natural Resources Defense Council and the U.S. Forest Service coordinated an aerial survey of whitebark pine mortality throughout the 20-million-acre Greater Yellowstone Ecosystem. The study found 46 percent of whitebark pine forests had high mortality, and another 36 percent with medium mortality.
The study stated, “This widespread high-intensity mortality may likely impact the ability of this species to provide critical ecosystem services, and may threaten the very future of this ecosystem.”
Connie Millar, who has studied high elevation pines for 25 years, says groundtruthing— walking the land to learn the extent and cause of mortality—tells scientists if there are live trees remaining, if young trees are regenerating and whether there is blister rust.
“The combined effects [of beetles, rust and drought] are causing more massive mortalities,” Millar says. Whitebarks are now a candidate species for the endangered species list.
AN ECOSYSTEM
In the Greater Yellowstone Ecosystem, whitebarks grow between 8,000-9,700 feet. There, they stabilize soil and shade the spring snowpack, supplying rivers with consistent runoff into summer.
Because they live in harsh climates with poor soil, they grow slowly. The 2-3’ diameter trees on Lone Mountain in Big Sky, for example, are several hundred years old. Without the shade they provide, a faster spring runoff would affect farming and river ecosystem health.
Whitebark pines have symbiotic relationships with Clark’s nutcrackers, red squirrels and bears, and support many other species of mammals and birds. Because of this, they are considered a keystone species – one that is critical to the larger ecological community. In the fall, whitebark cones produce pine nuts, which are rich in fat. Red squirrels hide the nuts in caches, and grizzlies raid them. Clark’s nutcrackers, which co-evolved with whitebarks, also cache the nuts in the ground: one bird will have up to 10,000 caches, and the ones they forget may germinate and become seedlings.
Tim Bennett, a bear biologist with Keystone Conservation working with the community of Big Sky on bear conflict issues, says whitebark pine nuts are an important food source for bears, particularly pregnant sows, or those with cubs. But whitebark cone crops have natural fluctuation in productivity, Bennett says, and during years of low cone production, bears descend to find other food, and bear-human conflicts increase.
Alternative perspectives to the demise of whitebark pine are rarely considered but should be by managers, according to Matt Lavin, a botany professor at MSU. “One such perspective is provided by anthropological research, as summarized by Charles Mann in his book 1491,” Lavin says. “High-density bison populations could have been the result of a release of hunting pressure after the demise of the great American Indian civilizations by small pox, influenza, and other human diseases.”
Lavin makes an analogy: Likewise, the many pine species in North America that grow as near monocultures could be a result of American Indians extensive burning of pine forests. “After the Indians’ demise, colonizing pines took over and became abundant during the 1900s, spurred by fire prevention programs. Now, these dense pine stands are fodder for blister rust and beetles.”
MOUNTAIN PINE BEETLES
During summer in Montana, adult beetles bore into a pine’s bark and lay eggs. As they burrow, they secrete a pheromone that attracts other beetles. The adults die in the fall, and the larvae hatch in spring, forming food channels that eventually girdle the tree by cutting off its nutrient and water flow.
The adult beetles emerge in mid-late July or early August. Historically beetles in the Greater Yellowstone had a two-year life cycle, Bennett says. “There is concern, and some evidence, that warmer, longer summers (climate change) will shorten their life cycle to one year.”
Beetles also carry blue stain fungi, which provides them with nutrients, but clogs a tree’s circulatory system. This causes the blue coloring in beetle-killed lumber.
“Beetles thrive during drought, [particularly] in stands that are tightly packed together and can’t get enough water,” says Millar, a Research Ecologist for the USDA Forest Service’s Pacific Southwest Research Station. She says beetles don’t kill 100 percent of the forests they attack. Once an epidemic is over, there are usually still live trees, which are often more resistant against future outbreaks.
BLISTER RUST
Blister rust is a fungal disease that came to America on nursery stock of eastern white pine (a relative of whitebark pine) in the early 20th century. Because the rust doesn’t move tree-to-tree—it has to go through a secondary host called Ribes (a currant or gooseberry bush)—it is slower to spread. According to Bennett, recent research documented blister rust having many more secondary hosts (for example, Indian paintbrush.) This is important, he says, because Ribes eradication campaigns have been unsuccessful.
Decades of research have been conducted on this pathogen, but its spread to higher elevation pines is new, and scientists don’t entirely understand how and why it spreads. Although whitebark is one of the more susceptible pine species, some appear to be resistant to the disease.
DEFENSES
In the heart of winter, beetle larvae are buried in the bark, protected. There, they metabolize glycerol, which acts as antifreeze. However, an early intense cold snap, or one late in the spring, can wipe them out, as will a couple weeks at 30 below, midwinter.
The 2009 aerial study found whitebark pines were less affected by beetle outbreaks in the core of the Wind River Range and the Beartooth Plateau – places not as affected by climate change. There, dwarf whitebark pine forests (called Krummholz) are resistant to beetle attacks, but still susceptible to white pine blister rust.
Humans have tried to control beetle epidemics in several ways. Insecticides are applied to individual trees or small groups of trees to protect them from being attacked by the beetles. The insecticide must be sprayed from the bottom to almost the top of the tree trunk, and the most common are Sevin (carbaryl) and Astro (permetherin). Sevin can be purchased by a private landowner, while Astro can only be purchased or applied by commercial applicators. Both are toxic to aquatic organisms, bees and other beneficial insects.
Jim Cancroft, a Senior Forester with Northwest Management, Inc., says a new insecticide Safari, that only needs to be applied on the lower five feet of a whitebark pine has been tested in the Big Sky area with promising results.
Research Ecologist Robert Keane specializes in whitebark restoration using sivilculture (forest thinning) and prescribed burns, both of which help forests stay healthy and create habitat for Clark’s nutcrackers. Through his work at the Rocky Mountain Research Station/Missoula fire sciences lab, Keane has seen these techniques be particularly effective in conjunction with Verbenone, a synthetic beetle pheromone that works as an attractant.
Keane says beetles are now killing whitebarks that survived decades of blister rust infection, and fungicide to fight the rust is costly and ineffective. Some nurseries are cultivating rust resistant whitebarks, because “if we lose those rust resistant trees to the beetles, we may lose the whitebarks.”
IMPLICATIONS OF LARGE-SCALE WHITEBARK DEATH
Because whitebark pine nuts ripen as bears are entering hyperphagia in the fall (when they eat about 10,000 calories/ day prior to hibernating), they rely on the fatty nuts. The Interagency Grizzly Bear Committee predicts that in the absence of whitebark pine nuts, bears will seek out meat instead, but there is no prediction of where they will obtain it.
According to Bennett, “Hunter kills and garbage cans are the most likely sources.” The bears in the Greater Yellowstone are already “more reliant on meat than bears in other areas because of low berry production [here].”
Whitebarks also protect watersheds. Most precipitation in the Northern Rockies falls as snow, with the largest amounts at high elevations. According to the Missoula- based Whitebark Pine Ecosystem Foundation, “The physical position of trees on the landscape and the up-swept branches of the crown provide shade to delay snowmelt and to retain snowdrifts until early to mid-summer.” Without that retention, peak runoff will occur earlier and summers will be drier, affecting river ecosystem health and agriculture.
PART OF A LARGER BALANCE?
Is this massive mortality doom for any species? ”Dying trees, in and of itself, is not a problem if the regeneration isn’t wiped out,” says Millar. “This is what these species have been doing for over 100 million years.”
It’s the combination of beetles and blister rust that often eliminates the possibility for effective regeneration, she adds. Blister rust can kill saplings, and beetles attack trees larger than a foot in diameter.
“Between the two, if you don’t have young trees growing or adult trees reproducing, then you don’t have a species.”
