The tremble tree.

A number of years ago I carved my name into the bark of an aspen tree. A job that summer kept me up in the aspen of southwest Colorado, alone, for weeks at a time. Maybe I was prodded into the carving by the shepherds. It's not that I'd seen any sheep or shepherds, but I'd traced their lives through generations of carvings on that tree.

"Henry Martinez-1951, 1952, 1953, 1954 . . ." The years were arranged vertically in a column-one for each time Henry had brought his sheep through that aspen grove and stopped to carve. Another whose annual comings and goings were recorded was J. Salerno, and toward autumn Joe Rael and I must have just missed crossing paths.

Other carvings were unsigned. Most were simple pictures etched int the aspen tree. Some were lewd. A few that turned the tree's physiology into a human being's bordered on art.

Much of the carving occurred from the 1940s until the late 1960s. Those were big sheep years in southwest Colorado, when hundreds of shepherds moved their flocks to the thick forage and bedding afforded by the aspen and nearby meadows.

Somehow the bark of the aspen invites marring. Shepherds and lonely foresters aren't the only villains. I've seen the claw marks of black bears and trunks pocked by the scratches and gouges of any number of snowshoe hares, elk, and voles.

The draw may be aspen's "live bark," which differs from the thick, dead outer cork layer that is commonly referred to as the "bark" of a tree (technically bark is cork plus the layer underneath it, the phloem).

In aspen trees the whitish, chalky "bark" you see is actually the tree's phloem layer which is alive. This live bark is even capable of photosynthesis. When the smooth white trunk is marred (or carved), a black, corky, dead scar tissue more akin to what is commonly known as bark does form. It is this scar tissue that raises and emboldens the names of the likes of Henry Martinez and J. Salerno a little more with the passing of each year. This same bark also grows in furrowed ridges at the bottom of the trunks of older aspens.

I probably carved my name in the aspen above Spring Creek for all of the same reasons anyone does it. I like to think I had more claim to it because I lived and worked in the aspen that year, but I probably didn't. If you find carving in trees distasteful, and there are good reasons for that feeling, then it was a repellent act. My only defense is aloneness and the idea that I wanted part of myself to stay in that country forever.

Aspen is the most widely distributed tree in North America. This member of the poplar family ranges across the northern part of the continent from Alaska to Newfoundland and south as far as Virginia. In the West, aspens string south along the Rockies into northern Mexico.

Locally, aspen are known by a variety of names, most of which refer to the way the leaves flutter in even a whisper of a breeze. Some folks where I live call them "quakies." Others might say "quaking aspen." Even the scientific name, Populus tremuloides, bears witness to the way in which the long, flattened leafstalks allow the aspen's leaves to tremble in the breeze. At a distance and with the right sort of breeze, a grove of aspen shimmers like a mirage.

I am prejudiced when it comes to judging aspens. I think the very best of them grow in southwestern Colorado. An number of factors may make it so, but for me the proof is as simple as turning off the highway just north of Purgatory Ski Area near Durango. There's a Forest Service road there with a couple of switchbacks at the bottom. Close to that looping road you'll see aspen with heights of 90, maybe even 100 feet. The trunks of those trees are clean and white with no sign of the rots and fungi that so often plague aspen trees.

These are glorious trees, but they don't hold a candle to what you might see if you get off the road farther west in the Dolores River drainage. There you'll see acres of aspen. The light itself is changed as it filters through the canopy and down white, straight-trunked trees that fan out endlessly into the distance. When you are among these trees, they have a way of completely filling the mind. No room is left for other thinking.

The life of the aspen is strange indeed. The most interesting feature is the tree's habit of clonal growth. Although a grove of aspen may consist of hundreds of trees, in terms of genetics they all may be exactly the same individual. New stems are produced by sprouts from the roots of the clone tree, and the sprouting continues throughout the life of the clone.

A stand of apparently similar aspen may consist of trees sprung from several different clones. These can be distinguished by looking for differences in the character of the bark, observing when the trees leaf out or change color in the fall, noting height differences, and finding other physical dissimilarities.

Throughout the entire range of the aspen, clones average about a half acre in size, although in southwestern Colorado you will find they are larger, in the two- to three-acre range. Southwestern aspen also live longer, up to 150 years, as compared with aspen in the Great Lakes region, which average 60 to 70 years.

Although aspen can regenerate by seed, the seedling's survival is dependent on a number of stringent climactic factors that tend to limit successful sexual reproduction. Seedlings that do survive contribute important genetic diversity to the stand.

Some aspen clones provide textbook examples of succession. This type of clone, known as seral aspen, will eventually be overtopped by conifers. Aspens do not generally grow in shade themselves, but the seral aspens provide shade for young conifers, which are a shade-tolerant species. As the conifers continue to grow, they eventually dominate the aspen and cause it to decline. The conversion often takes several generations.

Other clones are known as climax aspen. Very few conifers are found in these almost pure stands of aspen, which can be expected to remain indefinitely as self-sustaining groves.

It is among stable climax aspen stands growing in deep soils that you realize the unique paradox of the aspen. Many of these clones are at least a thousand years old! Some may even date, unchanged, back to the last Ice Age.

U.S. Forest Service ecologists Barry Johnston and Leonard Hendzel make the point that in the Rocky Mountain region where they work, aspen may be the longest-lived species, even though the individual stems are among the shortest-lived trees.

Where I live in the Rockies, aspen is the dominant hardwood and in many cases the only hardwood in an ocean of conifers. The open, sunny groves that it forms contrast with the darker moods of the big spruce-fir or lodgepole pine forests.

A great commerce of life goes on under the canopy of an aspen stand. The groves in the mid-elevation ranges are crossroads of wildlife and plant activity. The twigs are browsed by both deer and elk, and in the winter months hard-pressed elk often eat the bark. Aspen is also the favored food of beavers, and in areas where their numbers are concentrated, they will literally clearcut entire groves.

Rabbits and snowshoe hares eat the bark, leaves, and buds. At times grouse and quail feed on the buds. Cavity-nesting birds occupy the numerous snags that are characteristic of many aspen stands. Trout rise in the creeks and brooks that course through the groves.

The understory shows none of the sparseness I associate with the arid western states. The ground may be covered in several layers of vegetation that range from grasses to six-foot-high stalks of Ligustium or, in moister areas, cow parsnip. Other stands with different soil types may be covered with grasses and shrublike mountain snowberry. At lower elevations you find serviceberry and chokecherry, which is prized browse for both deer and elk.

And there are the wildflowers. Depending on the season and the particular aspen grove you are walking through, look for geraniums, blue-bells, larkspur, vetch, strawberry, groundsel, yarrow, columbine, lupine It has been said that there is no greater concentration of species of blue wildflowers anywhere, let alone the many other flowers represented.

It is the lushness of aspen groves that draws the big game. Although you may not see the elk themselves, it isn't hard to note their presence. I look for their matted-down "beds" in the grasses around knolls or on the edge of one of the benchlike slopes where these trees often grow. From positions on the benches and knolls, the wary elk can smell or sight anyone coming into their domain and, in the case of the knolls, ease off the back side. For an animal as big as the elk is, it is a wonder they can become so invisible.

I watch for elk in both spring and autumn. This isn't to say that you won't find them in the aspen during the summer or winter if the snow isn't too deep; it's just that spring and fall have their special pageant. In the springtime the cow elk often come to the aspen for calving. The series of benchlike slopes are ideal.

Once the calves have arrived, you may find that you literally stumble onto them. The elk employ what is known as a "hider strategy" in which the cows disperse widely before giving birth to avoid predators that follow the herds.

The young, which are colored to blend with the surroundings, have very little scent for weeks. Their strategy for survival is to hide alone in a flattened position while remaining very still and quiet. The mother, whose scent might attract predators, separates herself from the calf except for a brief feeding period.

I have literally stepped over hiding calves. Many will stay completely still in the flattened hider position even as you watch them. But there is also another scenario in which the calf lets out a loud, frightened bleat. You'll know it when you hear it. Not only will it scare off a hungry coyote or unsuspecting human, it may bring the cow elk in from a distance to defend her calf.

In autumn the scene changes to that of the rut. In the rutting season the aspen groves are filled with the high-pitched bugling of bun elk as they stake out their claims to harems of cows.

I once raced through the aspen toward the sound of a bugling bull. Instead of making a stealthy approach, without thinking I came in crashing, which made the elk think I was another bull charging in to steal his cows. As I closed in, I caught a glimpse of a big six-pointer pawing the ground and shredding shrubbery with his antlers. I could feel the air vibrating with the power of that magnificent animal. In fact, it was vibrating a little closer than I preferred-I backed quietly behind a nearby aspen.

When I was younger, I was on a crew that fought wildfires in the West. We held aspen in high regard because we knew that if we could tie our fireline into a grove of aspens, they would act as a firebreak. That isn't to say they wouldn't ever burn, but just that we knew it would take an awful lot of heat to make them catch fire, especially if they were climax aspen with little or no conifer growth. We called aspen the "asbestos plant."

We also learned that along with their "firefighting" characteristics, aspens play an important role in reclaiming burn sites. Aspen is uniquely suited as a pioneer species. The roots of the aspen clones quickly sucker into burned areas and produce hundreds or even thousands of stems in a short time, The devastated, bare ground plus the resulting abundant sunshine are the perfect combination for aspen. The fact is that many of the aspen stands that lure visitors to the West with bright autumn colors were once the sites of wildfires.

Nor does aspen restrict its pioneering to burn sites. Aspens play a role in the revegetation of any forest site that has been disturbed by logging, mining, or soil shifting and slumping. They will also come into abandoned fields and creep" into meadows when conditions are right. The unique ability of the aspen to heal disrupted lands has long been noted by foresters. In an 1888 Department of Agriculture forestry bulletin, the author wrote, "It is nature's restorative-the balm poured upon grievous wounds!"

Wayne Shepard, a research forester stationed at the Rocky Mountain Forest and Range Experiment Station, says that actually aspen may not be finding enough wounds to heal, particularly in the southern Rocky Mountains. "We did such a good job of suppressing forest fires down there for the past 100 years that the aspen have almost become an endangered species," he says. "They need that disruption to regenerate. The clones that are still there are being taken over by conifers."

As time has gone by, timber companies have alternately gained and lost interest in the aspen. Since most aspens tend to become infected with various fungi and rot by the time they reach sawlog sizes and because the wood is structurally weak, the species is of little value as dimensional lumber. The lumber does find some application in the making of pallets, and when used as flooring or siding in barns its unique grain stands up well without splintering to the kicking and chewing of barnyard animals.

The wood does shred well and is particularly useful as excelsior. In the Great Lakes region, the aspen has long been utilized as pulp and makes strong paper when mixed with pulp from other species. Aspen lends itself to pulping because it is cheap, easy to peel, and bleaches well. In the Rocky Mountains, the aspen was the last tree species to be considered as having commercial value. A number of factors pushed what timber-men once considered a weed into the commercial arena. Most importantly, many of the more highly valued species have been logged to the point that remaining stands occupy land that is economically or technically difficult to log. Many of the accessible logged-over sites are now occupied by aspen.

In addition, technical advances in waferboard and panel construction have developed a market for large volumes of aspen. Finally, aspen is cheap to purchase, and foresters are confident that they can easily regenerate it after logging.

All these bits of information I've given you can be combined to form a certain kind of image of the tree itself, but they are just simple facts. Sure, aspen is a firefighter's best friend, it provides basic housing for d thriving and diverse community of animals and plants alike, and it makes great wafer-board and matchsticks.

But there is more. Lately I have come to understand that aspen trees are spirited. By that I mean that if I try to tell you every conceivable detail about them, there will still be something more, something left over that doesn't fit neatly into the pigeonholes ecologists have so thoughtfully provided. It would have something to do with the way the autumn sun backlights a distant stand of absolutely golden aspen. It would be a single clone that alone turns golden in a sea of otherwise green aspen. It would be the way a stand of aspen fills my mind.

I had a funny boss that season I worked in the aspen. Now and then he'd venture out into the woods to check up on me. I always knew he was looking for me before he came into sight because when he was nearby the chorus of songs from the many different kinds of birds that lived there would abruptly stop. It was like the entire stand of aspen was holding its breath in anticipation.

He could never understand how I always knew he was coming. He finally asked me one day.

"The aspen stop breathing," I told him.

"Are you sure you don't want to come into town for a while?" he said.

"No way," was my reply.