Stalwart species: tenacious and rugged, the fire-dependent whitebark pine endures where most other trees fail

American Forests, Summer, 2002 by Gary Lantz

Whitebark pine tends to feel at home high above sea level, up on windswept slopes dominated by long winters and low temperatures. It's a tree that finds comfort in the wildest of our wild places, a specialist that approaches life with rugged attitude amid rugged altitude, in the skyscraping country of the northern Rockies and high Sierras.

This sturdy, five-needled pine prospers in monumental landscapes like the Grand Tetons, Yellowstone, and Glacier National Park. No stranger to extremes, whitebarks inhabit high-altitude environments near timberline, where other tree species find it difficult to establish a roothold.

Under natural circumstances, whitebark is the premiere pine high up in the subalpine and alpine regions of our northern forests, where spruce and fir tend to dominate until only alpine tundra can survive the wind and cold. Whitebark pine tends to be tenacious even at these lofty, frigid extremes--but only as long as an exacting ecological regimen remains in place.

The tree's overall value to both humans and wildlife might seem minuscule, considering its habitat. But the species' presence on never-summer slopes tends to modify the microclimate, influencing fragile high-altitude life processes just enough to stabilize a number of critical natural functions at a variety of elevations.

Foresters point out that whitebarks serve as "nurse" trees, protecting subalpine fir seedlings as they struggle to survive at the high elevation limits of their range. And, because the multi-trunked, shrubby species grows well on windy mountain ridges and produces broad crowns in the process, the trees act as high-altitude snow fences, regulating spring runoff and reducing erosion.

Trout fishermen applaud the pine's effect on mountain stream hydrology, just as bear lovers grasp the importance of having and keeping healthy whitebark communities. The tree's large, nutritious oil-rich nuts provide an important food source for numerous species including a powerful symbol of American wilderness, the grizzly bear. Ironically. this massive species must rely on a relatively tiny one for the perpetuation of that food. Whitebark pine relies on the jay-sized Clark's nutcracker to help it release those prized nuts.

Clark's nutcrackers perform an invaluable symbiotic service for the whitebark pine community. They retrieve the pine nuts from the purple cones, store up to 150 in a pouch below their tongues and then cache each seed by drilling holes in disturbed meadows, sowing their precious cargo much like a farmer presses a kernel of corn into the ground.

The birds depend upon memory to retrieve the nutritious food source as needed and tend to favor recently burned forestland for their larders. Not all the seeds are recovered, allowing a new generation of whitebark pine seedlings to spring to life in the raw, wet, high mountain environment it relishes.

Nutcrackers are not the only birds to prize the trees. Flickers and bluebirds seek them out for nesting cavities and red squirrels eagerly cache the high-energy pine cones.

In average years, grizzlies as well as black bears consume the tree's fatty cones from August through late autumn. When bumper crops abound, even bruins just emerging from hibernation will immediately seek out whitebark cone caches that survived the winter unscathed. Some researchers insist hungry grizzlies can locate these caches under 6 feet of snow.

Whitebark pines are what silviculturists term a keystone species of upper subalpine ecosystems. As such, says Melissa Jenkins, forester for the Caribou-Targhee National Forest, whitebarks determine numerous other species' ability to persist within a biological community that doesn't allow much latitude. In other words, the whitebark's ecological impact comes down to this: When keystone species are lost, biodiversity suffers.

Whitebark pines take a long time to regenerate naturally, and years of well-intentioned fire suppression have hindered the process. Without our help, Jenkins says, the fate of this cloud-clinging species depends on the nutcracker's ability to gather and plant the seeds, usually on recently burned sites, in clusters of anywhere from three to 15 kernels per excavation.

"Nutcrackers can cache up to 100,000 seeds per season during good cone years, and they'll fly as far as seven miles or more to do so," Jenkins points out. "Yet they only need about 25,000 nuts per year to feed themselves and their offspring, so a large number of seeds remain to germinate and reestablish seedlings."

Forest fire usually invokes an image of blackened trees, but whitebark seedlings can tolerate harsh, post-fire conditions. This trait, along with the nutcracker's willingness to fly far with the seeds, helps the pines regenerate deep into the charred heart of seemingly inaccessible burn sites.

Due in part to the intricacy of the tree's reproductive process, all is not well currently with whitebark pine populations. The trees are declining in areas they once dominated. "About 98 percent of all whitebark communities occur on federal land," Jenkins says. "Throughout these areas trees are failing to recruit naturally while, at the same time, many are dying due to mountain pine beetle infestation and imported white pine blister rust."