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Mancos - Aspen forests in Colorado and throughout the West are fading from the landscape, dying faster and in more places than previously expected and for reasons scientists don't understand.

In every Western state, aspen mortality is increasing, U.S. Forest Service ecologists say.

In the past two years, large-scale die-off of thousands of acres has been documented for the first time in Colorado by aerial surveys of prime aspen country on the Western Slope.

"The aspen is in universal decline in the Intermountain West," aspen researcher Wayne Shepperd said from the Rocky Mountain Research Station in Fort Collins. "I haven't seen anything like this before in 37 years in the Forest Service. But it's suddenly very noticeable."

The aspen, the most widely dispersed tree in North America, is abundant on 3.6 million acres in Colorado. In terms of numbers of acres of shimmering white glades in the West, half of them are in Colorado.

"The Colorado blue spruce might be the official state tree, but aspen pays the rent," Shepperd said. "It's really the icon in Colorado. We're going to have some holes in the Western landscape."

While the state doesn't track the dollars, the fall foliage creates a tourist draw after summer recreation has wound down and before skiing begins. Hunters and leaf lookers are a mainstay of Colorado's fall season, when 20 percent of "overnight pleasure tours" take place in the state, according to the most recent state-commissioned study, in 2004.


Aspen is a hardwood commercially harvested in western Colorado and, wildlife managers say, is popular with wildlife for food and cover.

Aspen ecologist Dale Bartos, based in Logan, Utah, estimates that 10 percent, or hundreds of thousands of acres, of aspen in the West ultimately could fail.

Shepperd fears that's a conservative estimate.

"We don't know how far it will go because we don't know what's causing it," he said. "I hate to sound alarmist, but I am alarmed."

Research stations around the West report that the trees are dying at high and low elevations. They are dying on north-facing and south-facing slopes. They are dying where there is intense grazing on young aspen and where there is no grazing. They are dying where fires have raged and where they have been suppressed. They are dying where logging has been common and where it has never happened. They are dying in drought-stricken areas and in fairly lush areas. They are dying where conifers are crowding them and where they aren't. Tall and short, young and old - although more old - are dying.

Shepperd said this type of dieback phenomenon was not witnessed at any time in the past century.

Recent investigations of dying stands show that the roots are dying. Aspen sprouts are formed on the roots, so this tells Shepperd that these stands won't be making a comeback.

Foresters have known for decades that the West's aspen population, with many trees 120 to 130 years old, would face greater mortality because of age and a number of environmental stresses - drought, insect infestations, disease, fire suppression, and overgrazing of young aspen by livestock and wildlife.

But the accelerating rate of death, the widespread mosaic across the West without discernible pattern and the loss of root systems are disturbing to researchers.

"There is something else going on," Shepperd said. "We just can't put a handle on it."

Aspen is considered to be one of the planet's largest organisms because a stand's trees are interconnected at their roots. Aspen typically reproduce asexually by suckering - generating new sprouts from the roots.

When aspen leaves die, the trees stop producing a chemical growth inhibitor. When it stops flowing, the roots are signaled to produce new trees to replace the dead. That's why recent findings of dead root systems are so significant.

In the San Juan National Forest in southwestern Colorado, aspen appear to be in the most trouble. Thousands of acres are dead or dying.

"The San Juan aspen is the ultimate expression of aspen on the American continent," Shepperd said. "The stands are larger. The trees are bigger. But we found a really accelerated mortality rate there in June ... and dead roots."

Forester Phil Kemp of the San Juan's Dolores Ranger District said he started noticing the dieback several years ago but became very worried this year when aspen stands in the Turkey Knolls area, which had been around 10 percent dead in 2002, were 60 percent dead.

"It's disturbing," he said. "If this continues, it's going to have a dramatic effect on the look of the forest."

There are other ramifications.

The aspen buds and catkins are valuable food for ruffed grouse. The tender bark, twigs and foliage are eaten by small mammals such as rabbits and by big game such as deer, elk and moose. Porcupines and beavers love the bark. An aspen glade, unlike a conifer thicket, often supports a lush understory of grasses and other edible plants. Bears frequent aspen stands. Many types of birds depend on tree cavities for homes.

And the die-off spells trouble for the three commercial aspen harvesters on the Western Slope.

"It's scary. About two years ago I started noticing all the dead trees on the hillsides," said Mary Ann Findley, co-owner of Aspen Wall Wood. "We can't use the dead trees. We need green trees to make our tongue- and-groove paneling."

Many disturbances, such as clear-cutting, forest fires, avalanches and landslides, actually encourage generation of aspen, a quick-growing, sun-loving tree that is among the first to establish itself in a clearing. Aspen are eventually driven out of many areas by slower-growing conifers that ultimately crowd and shade them.

But a century of fire suppression has diminished one of aspen's biggest advantages. Aspen regeneration in burned areas of Colorado, such as the Missionary Ridge and Million fires, has been encouraging, Shepperd said. But the good news is local. The bad news is widespread.

Aspen historically have been able to withstand herds, droughts and blights without massive die-off, Bartos said. But the aspen's heyday could be over. The phenomenon could point to a loss of genetic vigor.

"They seem more susceptible," Bartos said. "I don't know if this is just a natural resetting of the table."
