ARIZONA'S OLD GROWTH FORESTS

NATURE'S OWN TIME CAPSULES Old Growth Forests

I SCRUNCHED THROUGH THE CRYSTALLINE late-winter snow to the base of a towering pondersosa pine that had first put down roots before the Pilgrims landed. Pulling loose a piece of bark, I inhaled the distinctive ponderosa scent of vanilla, a bouquet produced by the complex mix of chemicals that helps defend the ancient tree against insects, disease, and drought. The massive pine, too big for two people to encircle with linked hands, reared dizzyingly upward, the first branches 20 feet above the surface of the unmarred snow. Rooted in a dimsheltered world and crowned in brilliant sunlight, the rough-barked giant had been the center pole of an intricate ecosystem for four centuries. Nourished by mushrooms, assaulted by beetles, preyed on by mistletoe, harvested by squirrels, seared by fires, and host to multitudes of birds, the enormous yellowbelly pine was a survivor. Once such giants covered much of northern Arizona. Now only about five percent of the state's old growth forests remain, thanks to generations of logging, grazing, and development. The old forest hangs on atop a few

Old Growth Forests

mountains, in inaccessible canyons, and in a few protected places like Grand Canyon National Park.

The silence washed over me as photographer Christine Keith worked nearby setting up for a shot of the giant trees in the luminous light of dawn. At that moment, I wouldn't have been surprised to hear the melodious measures of the Mormon Tabernacle Choir, sighing like wind through the branches.

Instead I heard a raucous screech. Jolted from the trance of the trees, I floundered through the maze of trunks toward the hidden hawk. Again the screech. There she was. In the dying top of an ancient tree perched a goshawk, a large, long-legged, wing-barred hunter that thrives beneath a closed forest canopy. The goshawk is a perch hunter, waiting patiently for hours high above the forest floor for an unwary rodent. The goshawks have become the poster birds for old growth forests because they depend so heavily on them. If the forest becomes too open, they lose out to other hawks like the redtail, which is better adapted to hunting in the open.

I stalked the hawk. She ignored me. I lay in the snow beneath her perch. She held her high ground, screeching occasionally.

Was she calling for a lost mate? Playing a game of nerves with terrified squirrels crouching in cover somewhere nearby? Or merely savoring the echoes of her voice through her hauntingly beautiful snowmantled domain?

The whole forest ecosystem was in sight as I lay in the snow, the cold seeping through my coat. It was the gestalt moment in a crash course in forest ecology administered by experts from Northern Arizona University, the Arizona Game and Fish Department, and the Forest Service. The goshawks eat the squirrels, which eat the cones and spread the fungi that nourish the trees, which are killed by the bark beetles, which feed the birds and provide nesting snags for the array of birds that feed the goshawks.

The old growth forest ecosystem has flourished in surprising diversity and flux since the glaciers retreated 10,000 years ago, leaving forests scattered throughout Arizona. On the high, wet, bitterly cold slopes of places like Mount Graham, Humphreys Peak, and the White Mountains, old growth forests of mixed conifers provide a diverse living system with giant Douglas firs, groves of aspen, thickets of corkbark firs, and dense stands of graceful Engelmann spruce. On the lower gently sloped Mogollon Rim grows theworld's largest pure ponderosa pine forest. The giant yellowbelly pines prized by loggers for their lack of knots and twists thrive on soils laid during the Ice Age on an average rainfall too sparse to sustain almost any other pine.

"The sum of an old growth forest is greater than its parts," notes Northern Arizona University professor Dr. Russ Balder. "You can't understand the forest by looking at its parts in isolation. It's like looking at individual cells and trying to predict the function of a kidney. All these forests are sustained by complex and still poorly understood cycles of growth and decay. Each part of the forest affects all the other parts, which is why a pristine old growth forest has so much more diversity and resiliency than the vast stretches of same-aged trees produced by logging.

"We need to have all the pieces. If you're going to maintain something, you've got to save all the spare parts," said Jim Beard, a landscape architect with the Coconino National Forest.

Enter the circle anywhere. Start at the roots. To acquire water and minerals, pines and firs all depend to some degree on mushroom-sprouting fungi that colonize their roots. A different species of fungi grows on each type of tree. The fungi, in turn, depend heavily on squirrels to spread their spores from tree to tree. It's a fair trade: The fungi truffles keep the squirrels alive during crucial parts of the year.

Old Growth Forests

In the lower-altitude ponderosa pine forest, Abert's squirrels play this role.

In the colder mixed-conifer forests, red squirrels serve the same function. They cope with the colder winters by building middens, piles of sticks and debris in the lee of a fallen log where they hoard cones. The middens must have just the right temperature and humidity to keep the pinecones from either drying out or sprouting, which means they must be built in dense forests where the interlocking branches of the trees filter out much of the sunlight. Such a closed forest canopy cools the forest floor in summer and slows escaping nighttime heat in winter.

The usefulness of the tree continues even in death. Consider the role of a snag, an unexpectedly vital part of a forest ecosystem. Trees, insects, and birds are locked in a complicated interchange in which the death of a tree begins a whole new cycle. Dead trees can remain standing for more than 50 years, sloughing their barks, rotting on the inside, slowly softening and decomposing under the assault of wind, rain, and frost. Once the Forest Service considered such snags fire hazards and paid for their removal. Now biologists have discovered that many birds depend on snags to survive. Some studies suggest that 80 percent of the bird activity in old growth areas is centered around the mature yellowbelly pines and snags.

That might be because old trees and snags attract a host of insects, including many varieties of pine beetles. Perhaps the pine beetles focus on older trees because the giants' chemical defenses have begun to falter. The first colonizing beetles emit some sort of chemical scent which draws other beetles. Rapid-fire generations of pine beetles chew large chambers in the inner bark of a tree and introduce a fungus that hinders the movement of water from the roots to the branches. That cripples the tree's chemical counterattack against the beetles. As more and more insects colonize the tree, it slowly starves to death.

That triggers several interlocking changes. Birds flock to the tree, led by woodpeckers and others with beaks tough enough to dig out the insects. Those tough-beaked birds also hollow out nests in the decaying heartwood of the doomed tree. The woodpeckers and other primary cavity nesters raise their young in these protected chambers, sheltered from extremes of heat and cold and safe from roving predators. But they abandon their carefully constructed cavities after a single nesting season, a tactic they probably evolved to avoid a buildup of mites, parasites, and diseases.

That leaves the hole free for colonization by a host of secondary cavity nesters, such as the pygmy nuthatch, an endearing chirp of a bird with no neck, a stub of a tail, and a voracious appetite for insects. These little birds flit through the forest, hopping up and down the immense expanse of tree trunks, peeping incessantly, and gobbling up an array of insect pests. They're one of the few species of birds that stay through the winter. Their secret lies in finding holes in snags abandoned by woodpeckers which they can jam with dozens of warm little bodies, like so many college students in a phone booth.

So the pine beetles create the snags, which shelter the birds, which eat the pine beetles, and protect the trees.

Unfortunately, we logged forests for decades before biologists looked closely at the

Old Growth Forests

Continued from page 28 ecosystems of old growth stands. Managers running the forests as giant tree farms inadvertently created all sorts of intractable problems, ranging from mistletoe infestations to terrible fire dangers. Diseases, insect pests, and mistletoe all thrive in the densely packed single-aged stands of logged forests largely kept under control by the natural checks and balances in an old growth forest. Fire also has been converted from a boon to a bane. Fires don't do much damage in old growth forests because the shade of the mature trees keeps thickets of small trees from sprouting, and the lower branches of the mature trees are too high to catch flames ambling through the sparse debris on the forest floor. These slow, cool ground fires once burned through the forests about every five to seven years. They thinned out the young trees, kept piles of debris from building up on the forest floor, and returned the nutrient-rich ash to the soil. But now the fire-resistant old growth forests have given way to stands of closely spaced trees of uniform age. Fires now feed on decades-long accumulations of debris and leapfrog from the tops of the thickets of young trees into the branches of the mature trees, triggering devastating fires that jump from treetop to treetop.

"In Germany, they've been logging for 400 years, and the forests are simply falling apart," said Norris Dodd, a game and fish habitat specialist. "Some evidence shows they've depleted the soil. If we break up these relationships, the bottom line may be that we lose the ability to sustain the system in the long term."

Dave Patton, an NAU professor of forest wildlife ecology, commented, "We're trying to understand the interactions of more than 200 different species. It's so complicated that no one has ever really looked at the whole picture."

But sometimes you can catch a glimpse. Like the day we spent touring Fire Point on the North Rim of the Grand Canyon, one of the best stands of old growth ponderosa pine forest in the state. A few years ago, Fire Point caught fire. The National Park Service let it burn. The flames crept through the grove of trees that were already giants when George Washington's rebels eked out the winter among the pines of Valley Forge. The fire left few marks save for the remains of charred logs scattered about on the forest floor, their conversion to fertilizer hastened by the flames.Birds flitted through the branches. I tried to count the calls. The nuthatch I recognized. The jay I knew. For the rest, I simply closed my eyes and listened to the twittered harmony.

Then I wandered across the snow, looking for tracks.

I came suddenly to the edge of the world. The multihued Canyon dropped away at my feet, the vegetation making the swift transition from ponderosa monarchs, to piñon survivors, to prickly pear warriors, to hardy brush and cactuses in the depths of that billion-year slash in geologic time.

Out over the Canyon, a red-tailed hawk wheeled on the thermals. Behind me in the sheltering forest, I heard a screech. Was it a goshawk, challenging its circling rival from one of its last canopied bastions?

I drank in the Canyon for a while. Then I turned and wandered back into the forest, drawn to the more intimate marvels of tree and root and mushroom, seeing for the first time the wonder in the details.