It's been a splendid July day in Yellowstone. Cara and I have hiked through a blaze of wildflowers: elephant heads, monument plant, rein orchid, larkspur, monkshood, and more; watched a coyote pouncing its way across a meadow; and looped down Dunraven Pass as a thunderstorm spun a rainbow over Tower Falls. Now, on our way home, we scan the prismatic late-afternoon light for bears, maybe a moose or great grey owl, whatever the American Serengeti has to offer. As always, the Park has delivered a generous share of the wilderness "glad tidings" that the naturalist John Muir called his readers to get firsthand, an invitation that has brought acolytes to places like Yellowstone for well over a century.
The road between Tower Falls and Mammoth Hot Springs crosses the western reaches of the park's northern range, famous for its elk, bison, and the wolves that follow them. Parts of the range were seared by the great 1988 fires, but on the Blacktail Deer Plateau northeast of Tower Falls, wet depressions, sagebrush hills, and open groves of Douglas-fir and lodgepole pine are laced together by strands of aspen into one of Yellowstone's most diverse and striking landscapes. At least that's how it was. Today, driving toward Mammoth, we're surrounded by an alarming panorama of reddened needles extending out from both sides of the road. We can't say what's attacking the Blacktail Plateau trees, but north of the park boundary we find the Absaroka mountain slopes draped with a more uniform red zone, the distressingly familiar mark of the ongoing mountain pine beetle epidemic that has been sweeping through western conifers for the last two decades. Environmental writer George Wuerthner cautions that such outbreaks don't really kill all the trees, and generally look worse than they are. That may be, but the effect is shocking nonetheless, the bugs advancing through Greater Yellowstone's sacred space like an invading army.
Which, in fact, they aren't. The native insects ripping through western forests have coexisted with their conifer hosts for millennia, usually going about their business inoffensively at "endemic" or "background" levels, turning weak and diseased trees into useful snags and nest sites. Occasionally, however, beetle populations surge to epidemic levels, scattering across the mountains in plague numbers. Bark beetle outbreaks occurred during the 1930s, 1950s, and 1970s, but those were small potatoes compared to the pandemic now engulfing montane forests from Arizona to British Columbia. In Colorado, there's talk of lodgepole pines, a favorite insect target, becoming functionally extinct, and across Idaho, Montana, and Wyoming, slopes of dead trees are coming to dominate formerly wooded landscapes. Real estate hucksters are scrambling to market "new view lots," and ski resorts are taking chainsaws to what used to be their ambience, a liability- and public relations-driven preemptive strike against any potential convergence of tourist and toppling deadwood. The outbreak is being called the biggest event of its kind in North American history. Trained by experience to suspect human agency-of late especially climate change-in rapid wholesale environmental disruptions, it's hard not to see these bugs as a kind of fifth column, allied to unholy forces from without, that is to say, us.
Not denying the human signal in the red slopes, Wuerthner views beetles as the forest's way of pruning woodlands that, in a warming, drying West, have become "overstocked" with mature conifers. He reminds us that, despite their comfortingly timeless name, evergreen forests are dynamic systems in constant flux. Our present-day woods are a snapshot moment in a complex co-evolutionary history linking climate, trees, and insects. Systematic weather and forest-health records covering a century or two offer little perspective when placed in the long-term context of what might be called a forest's own reckoning of time.
Though insect-killed trees often burn or simply decompose beyond recognition, paleobotanists can sometimes piece together traces left by prehistoric outbreaks. In Of Rock and Rivers, Colorado State University's Ellen Wohl parallels an epidemic of hemlock looper bugs in the Northeast some 4800 years ago with the current mountain pine beetle surge. Those woods were thinly peopled, but the insects didn't need human help to catalyze wholesale changes in forest ecology. Loopers decimated eastern hemlocks, leaving scattered remnants from which the species eventually rebounded, eventually being somewhere in the neighborhood of 1500 years. Now relegated to cool, humid pockets in hardwood-rich eastern woodlands, hemlocks are once again under insect attack, this time by the introduced woolly adelgid. Who's to say what another millennium will bring?
Rooted in the meager soil of unstable slopes and routinely subjected to weather extremes, Rocky Mountain evergreen forests, especially those dominated by lodgepole pine, are prone to apocalyptic renewal cycles. The natural lifespan for a Rocky Mountain lodgepole ranges from 100 to 400 years. Ultimately, the mature trees fall victim to canyon windstorms, drought-induced wildfires, or insect infestations, often in stand-replacing single events. The woods reddening and dying throughout the West are largely even-aged old-growth stands dominated by one or two species, the kind timber industry p.r. used to label "overmature" to justify clearcutting. Such forests come and go across the fossil record, and even in recorded history. Some old timers shrug off the latest insect outbreak as more of the same, though most people who spend time outdoors in the West admit that they haven't seen anything quite like this epidemic in scope and duration. Tom Reed of Trout Unlimited points out that in Wyoming pine beetles are overwhelming trees from ponderosas on the mountain skirts to timberline five-needle pines-limber and whitebark. Sprouting nutritious calorie-rich cones, an autumn staple for creatures ranging from Clark's nutcrackers to grizzly bears, the whitebark pine is a particular concern in the high mountains framing Yellowstone Park, legendary ranges such as the Tetons, the Gallatins, the Absarokas, and the Beartooths, the northeastern rampart of Greater Yellowstone and the closest reach of the ecosystem to my Billings, Montana, home.
The Beartooth High Lakes Trail winds through a bouldery world of subalpine ponds suspended thousands of feet above the surrounding valleys and just below the Beartooth Pass tundra. It's the kind of place John Muir would have liked. It's also ideal whitebark pine habitat, which explains the grizzly-warning signs at the Beartooth Lake trailhead. But looking across the lake at the slopes of Beartooth Butte, an eccentric tawny limestone mesa adrift on a granite base, we can already tell that all is not right with the pines.
The trail begins with a steady two-mile climb through colorful wildflower meadows-mostly yellows and blues by mid-August-but it's another color that grabs our attention. Unlike densely-packed lodgepoles, mature whitebark pines develop spreading crowns, giving these "stone pines" a striking appearance perfectly suited to the dramatic talus-strewn mountainsides where they grow. When a centuries-old whitebark is killed by beetles, it makes a rusty sunburst-spectacular but disheartening. We find such ragged explosions blazing throughout the Beartooth lakes, with silvery previous victims interspersed like giant dandelions gone to seed among firs greenblack in the glare of high-elevation sun.
Whitebarks form distinctive groves or mingle with other timberline species in Yellowstone's mountains and in similar places from northern Canada south to Muir's Sierra Nevada. Though mountain pine beetles have historically infected whitebarks during unusually warm, droughty periods-the 1930s, for example-these long-lived slow-growing pines have not evolved the vigorous defenses characteristic of more common hosts; in an ongoing Greater Yellowstone study by Jesse A. Logan, William W. McFarlane and Louisa Willcox, "only a couple of the trees (literally two) have been found to be successful in fending off beetle attacks, using chemical and physical responses similar to those in lower-elevation tree species." Instead, whitebarks rely primarily on frigid temperatures to keep outbreaks short and self-contained, a strategy only as sound as the winters are cold and long. Willcox concludes that, under present conditions, "Whitebark pine is basically a sitting duck to pine beetle." Yellowstone whitebarks are particularly vulnerable in the absence of an extensive fir and spruce barrier separating them from lower-elevation lodgepoles, typically the source of epidemics moving upslope into timberline five-needle pines. The current Greater Yellowstone outbreak, however, seems to have started in whitebarks and moved downhill, perhaps further implicating high-altitude warming. The epidemic may have peaked, but not before reaching over 90% of area whitebark forests and causing major losses in over 80% of the affected groves. The climate bad news for the whitebark is not limited to beetle depredation; some of the healthiest remaining stands are in Great Basin ranges where their habitat could simply be warmed out of existence.
Despite the daunting complexities of forest ecology, it's pretty clear that, as Yellowstone essayist Jack Turner concludes, "to be blunt, the fate of the whitebark pine is our fault." Whitebarks have had a rough century. White pine blister rust, a fungal disease of Asian origin accidentally introduced into British Columbia, brought considerable mortality even before the beetles climbed the warming climate to the redoubts where whitebarks grow. According to the Whitebark Pine Ecosystem Foundation, headquartered in Missoula, Montana, a broad swath of the northern Rockies has lost over half its whitebarks from the one-two punch of exotic and indigenous attackers. Whitebarks find themselves in a classic double-bind. Cool, wet summers that relieve beetle outbreaks are conducive to the spread of blister rust. While beetles home in on mature trees, blister rust reduces cone output and can quickly overcome seedlings. Krummholz growth is largely ignored by bark beetles and could serve as a post-outbreak reservoir of healthy trees, but this gnarled, flattened growth-form is not immune to rust. The Forest Service concludes that, even without the beetles, "white pine blister rust can threaten the sustainability of high elevation white pine stands."
The pines' situation may be dire, but dedicated "whitebark warriors" are stockpiling the cones of rust-resistant trees with future restoration in mind. Whitebarks matter to Yellowstone people, for their beauty, their "ecosystem services" such as slowing and prolonging spring runoff, and their value to bears and other wildlife. Willcox's blog describes Livingston, Montana, caterer/restaurateur and grizzly aficionado Dan Sullivan tearfully blurting out that "the most beautiful bear scats were the blond ones, those filled with pine seeds," when informed of her group's grim findings.
Our Beartooth High Lakes hike ends in waning evening light as we descend back to Beartooth Lake through a robust forest of subalpine fir. The Whitebark Pine Foundation lists successional replacement as one of the more insidious threats to the whitebark's long-term viability. Twentieth century fire suppression may have neutralized a whitebark competitive edge-seeds cached by Clark's nutcrackers and ready to sprout in the wake of lightning fires. With pine cone stocks and seedling survival further compromised by disease, competing trees are likely to prosper at the expense of the pines. Like the hardwoods that moved into the gap left by looper-blighted eastern hemlocks, subalpine and Douglas-firs, despite their own predatory insects and fire-suppression history, may take advantage of an ecological opportunity spurred by pine beetle kill.
With close to a full complement of native species, the Greater Yellowstone Ecosystem boasts a level of integrity rare in the lower 48. In the case of the whitebark pine, that completeness is clearly on the line. On July 19, 2010, in response to a Natural Resources Defense Council petition filed almost two years earlier, the U.S. Fish and Wildlife Service announced a belated review to determine if the whitebark merited a place on the Endangered Species List. The Service's website explained that "Information provided in the petition, as well as other information in our files, indicates that listing the species may be warranted due to the white pine blister rust pathogen (an introduced fungal disease), mountain pine beetles, and climate change." A year later, the Service designated the whitebark a "candidate species," concluding that the whitebark needs protection but that listing at the current time is "precluded" by other priorities.
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