If the aspen has a heart, it’s in Colorado and Utah. Of the nearly 4 million acres covered by the elegant tree in the western United States, more than halfר.5 million acres—is found in those two states, much of it in pure stands. Some of the forests stretch for miles, vast swaths of green and gold carpeting the flanks of soaring peaks.

Aspen may seem ubiquitous in the Rockies, but its range is shrinking. The tree has been disappearing at such a clip that experts say it’s possible the species will eventually vanish altogether, at least in some portions of the West.

“Aspen is generally in decline in the West,” says Wayne D. Shepperd, research silviculturist at the U.S. Forest Service Rocky Mountain Research Station in Fort Collins, Colorado. “It isn’t going to crash overnight, but the trend has been going on for the past twenty years or so.”

It is estimated that about 9.6 million acres of aspen originally grew throughout the West. Since the arrival of European-American settlers in the mid–nineteenth century, some 5.7 million acres have been lost, a drop of about 60 percent. The main reason for the decline? Smokey Bear. Although the century-long suppression of wildfires has allowed a proliferation of dense stands of trees across the West, it has had the opposite effect on aspens, which need fire to regenerate.

The data show the decline is stark, and consistent across Western states. In Colorado, scientists say aspen numbers have declined by nearly 50 percent from historical levels. In Utah, the slide totals 51 percent. In Arizona, it’s as much as 96 percent. The decline in Idaho is 61 percent. In Montana and New Mexico, aspens have waned by 64 and 88 percent, respectively. Wyoming has lost 53 percent of its aspens. They continue to decline in Nevada, northeast Oregon and Northern California as well.

The aspen is the most widely distributed tree in North America. It can be found as far north as Alaska and the Yukon and as far south as the mountainous areas of the American Southwest and Mexico. There are stands on the Eastern Seaboard, in the Great Lakes region, even in the Great Plains states of Iowa and Nebraska. Aspen trees typically grow in well-watered areas at elevations anywhere from sea level to 11,500 feet. In the western states, where they are most abundant, aspens do best in areas that are above 2,000 feet in elevation and that receive significant amounts of snow.

Although they may reach over 100 feet high, aspens are more typically in the twenty- to seventy-five-foot range. They are short-lived trees with life spans of seventy to ninety years. But older trees are not unheard of. The oldest known aspen, at 275 years, was discovered last summer in western Colorado.

The tree’s scientific name, Populus tremuloides, alludes to the trembling of its leaves in the breeze. That soft fluttering is so familiar to walkers of aspen groves that it may be the only tree in the world identifiable, like a delicate forest bird, by the sound it makes.

The aspen’s value to wildlife is far greater than the sum total of its acreage. Aspen groves are inherently more productive than conifer forests, producing up to 3,000 pounds of understory growth per acre, compared to a conifer woodland’s mere 200. And that means more forage for elk, deer and moose, food for beavers, and cover and nesting habitat for a wide range of birds, from woodpeckers to neotropical migrants.

“When I talk about aspen, I try to project all the aspects of aspens,” says Bob Campbell, ecologist with Utah’s Fishlake National Forest. “That includes vertebrate and invertebrate organisms. Aspens are one of our most biologically rich ecosystems.”

Unlike the East, where aspen often regenerate via seeds, the West has drier, less hospitable conditions that require a different survival strategy—vegetative reproduction. An extensive root system lies just beneath the ground surface in an aspen grove. New shoots grow directly out of these roots. A stand of aspen that appears to be many trees is more likely one organism, all clones from the same parent root system.

And some aspen groves have been around for a very long time. “We have clones here in Utah that are hundreds of acres in size,” says Dale Bartos, aspen ecologist at the Forest Service’s Rocky Mountain Research Station in Logan, Utah. “If that started from a single seed, then that genetic material has been on-site for thousands of years.”

But the essential fact of aspen ecology in the West is that the trees have prospered by being continually destroyed by fire. “Aspen is a fire-dependent species,” Bartos says. “It thrives on getting killed.”

In a sense, aspens are always in decline, even in a naturally functioning ecosystem. Years after the last cleansing forest fire, a mature aspen grove is full of aging trees surrounded by ever encroaching conifers. Taller, the conifers block the direct sunlight that aspens need to survive. Choking from the invasion of conifers, an aspen’s own survival strategies begin to betray it. Auxin, a chemical compound created by mature aspens, regularly travels down the trunks to the root system, inhibiting excessive growth by new suckers that would otherwise compete with the tree. At this stage, however, the aspen grove needs new growth to replace the trees being crowded out by the conifers. Instead, such growth is retarded, hastening the grove’s destruction.

A robust aspen grove is a wall of green, composed of new shoots, saplings and large trees. Such greenery provides a measure of fireproofing, but the trees’ thin bark renders them easily killed by even light fires. It’s a strategy of survival by sacrifice: fire merely renews the cycle of aspen sucker growth. Because the aspens regenerate from an existing root system, following a fire they have a distinct advantage over conifers, which must recolonize by seeds.

“Historically, these sites burned up every forty to fifty years,” which maintained aspen dominance, or at least prevalence, Bartos says. “But since the turn of the last century, we’ve been very effective at putting out fires. This has allowed conifers to get established and take over.” And that, no pun intended, is the root of the aspen’s problem.

Many thousands of acres of aspens in Colorado, and to a lesser degree in Utah, grow in pure stands because there are few nearby conifers. But for the rest of the West, the aspen is a successional species found in mixed groves with such conifers as Engelmann spruce, alpine fir, ponderosa pine, lodgepole pine and Douglas-fir, depending on the location.

This distinction between pure stands and mixed stands is important because the decline of aspen is not measured in the disappearance of individual trees, but in the ratio of aspens to conifers in any given stand. In mixed stands, researches monitor the extent to which aspens are being overtaken by conifers.

There are other contributing factors to the aspen decline. Grazing by sheep and cattle—and even by deer and elk—is one of them, a practice that has eliminated the grasses that helped carry fire into aspen groves. And grazing hurts aspens in another way: by nipping new aspen shoots in the bud.

Although the decline of aspen is widespread and in some places serious—in Arizona’s Prescott National Forest, for example, there are twelve acres of aspens left, consisting of two clones—the situation is far from bleak.

“Some people think that if there is a decline, then the aspens will disappear,” says Brian Ferguson, regional silviculturist for the Forest Service’s Intermountain Region. “But we can go into an area where aspens are in decline and restore them.”

Prescribed burning is often the best and most efficient way to do that. One impressive example of the benefits of reintroducing fire can be found on Utah’s Dixie National Forest, where Ferguson formerly worked. In 1997, a forestwide assessment identified 20,000 acres that included an aspen-conifer forest as ripe for restoration by fire—intense fire. “We put in these spectacular stand-replacing fires,” says Ferguson. “They had tremendous flames, 200 feet high.” When the fireworks died down, the results were striking. Within six weeks after the burn, aspen sprouts began poking out of the ground from the still-intact root systems. By the following year, there were about 150,000 aspen sprouts per acre within the burn area. Today, three years later, the aspens are three feet tall, with a healthy 40,000 to 50,000 sprouts per acre.

Forest managers have other methods of bringing back the aspen. They can cut a ring around the trunks of aspens—a practice known as girdling—to stimulate new suckers. Or they can cut the main root of a large aspen, choking off the growth-inhibiting supply of auxin and giving the root system false signals that the main tree has died, causing new shoots to grow.

Logging aspens, although controversial, can be an effective approach as well. In Colorado, with its large, pure stands of aspens and sparse fuel for burning due to the lack of conifers, fifteen- to twenty-acre clear-cuts are used to mimic the effects of fire. These are often done in even-age stands to create a diversity of tree ages and sizes, to better mimic the more natural condition. “The fires were disturbing the landscape on a much larger scale,” Shepperd says. “So you need to duplicate those large scale disturbances.”

Although it can have the same growth-stimulating effects as fire, logging has its downsides as a tool for aspen restoration. Typically, logging is commissioned through commercial timber sales, a practice that environmentalists are quick to point out brings pressure to cut the most valuable trees and, in many cases, to build new roads—activities that don’t necessarily further restoration. Also, there’s a question of scale. “You can burn 1,000 acres in a week,” explains Ferguson. “But you’ll be lucky to harvest 300 acres in a year.”

Nonetheless, there has been large-scale logging of aspens in Colorado, particularly by timber giant Louisiana-Pacific Corporation, which operates a mill near the town of Montrose. Timber sales designed by the Forest Service and bought by L-P have been bitterly opposed by environmentalists, who say the logging is so intensive that it is destructive to aspen groves.

Grazing is another knotty complication for aspen restoration. Theoretically, federal land managers can work with grazing permittees to keep their livestock away from aspen groves during critical growth periods, but in practice, such protective measures are not always taken—either because of the long-standing pro-grazing bias of the Forest Service and the Bureau of Land Management, or resistance from ranchers, or both. Even when steps are taken to protect aspen groves, browsing by wildlife—elk and deer—is more difficult to prevent.

Elk can be especially destructive to young aspens, breaking off branches and gnawing at the bark, exposing the trees to disease and insects. A study in Wyoming’s Gros Ventre Range in the early 1970s found that most aspen mortality there was the result of either fungi or insects that invaded the trees through wounds made by big game. More pervasive is the simple act of elk or deer munching on new aspen sprouts before they reach the one and one-half inches or so in diameter that allows them to withstand this ungulate onslaught.

There are aspen groves so hard hit by elk each year on the Malheur National Forest in eastern Oregon—where aspens have declined by 80 percent from historical levels—that some of the suckers are only sixteen inches high, even though they are thirty years old. Such is the potential pruning effect big game can have. Fencing off regenerating groves and individual trees, though expensive, is often the most practical and direct way to deal with the browsing issue.

Growing numbers of elk in much of the West only exacerbate the browsing damage. “In many places it’s an increasing problem,” Shepperd says. “I’ve had reports of elk damage where it wasn’t found fifteen years ago.” And that’s where the wolves come in, in one of ecology’s deliciously unexpected relationships.

Since 1998, Oregon State University researchers Eric Larsen and William Ripple have been conducting a series of research projects in Yellowstone National Park, where the aspen decline is estimated to be anywhere from 50 to as much as 95 percent since the park was established in 1872. The primary suspects are fire suppression and overbrowsing by the park’s substantial elk population. But Larsen and Ripple have another theory.

“We think that possibly the elimination of the wolf might have had an effect on the aspens,” says Larsen. In examining historical records, they found that there was a cessation of new aspen overstory replacement in the park beginning in the early 1920s—around the same time that the park’s wolves were being killed off. They theorize that historically wolves not only kept the elk population in check, which cut down on browsing pressure, but also influenced elk travel and foraging behavior. For instance, elk may have avoided dense aspen groves where ambush by wolves was a danger or stayed away altogether from aspens located deep within a wolf pack’s territory.

It is too soon for the researchers to come to any conclusions. But if the theory holds true, the reintroduction of wolves to the park in 1995 may help restore Yellowstone’s dwindling aspen forests.

Forest managers say it’s clear that some direct restoration of aspen is needed, given the extent to which western forests have been altered. That’s what’s happening on the Malheur National Forest, where federal workers are using a variety of methods—fencing, burning, cutting—to restore the aspen.

“Some of us have been grinding away for years, and now we are starting to see more interest and recognition for restoring aspens,” says Michael Tatum, silviculturist for the Malheur’s Prairie City Ranger District. “We know what to do, and most of our projects are successful.”