Forest On The Edge

Blunders uproot old-growth ecosystem

Fire and Water: The Mogollon Rim forms a crucial ecological divide running through the heart of the world’s largest ponderosa pine forest.


Fire and Water: The Mogollon Rim forms a crucial ecological divide running through the heart of the world’s largest ponderosa pine forest.



File photo

Super hot fires in the thickets of pines on the Rim, like the Dude Fire, caused dramatic increases in erosion, sterilized the soil and posed the threat of catastrophic mud slides for Rim communities.


Tom Brossart/Roundup

Snowpack: Forest densities determine whether snowpacks provide spring floods.


Tom Brossart/Roundup

Photos by Tom Brossart/Roundup Water Balance: Many once year-round streams running off the Mogollon Rim have all but dried up, partly because tree thickets on top of the Rim drink up every drop of moisture, leaving little to run off to soak into the ground and gradually feed water into streams.


Tom Brossart/Roundup

Shaped by Fire: In a healthy ponderosa pine forest, low-intensity ground fires burn through every five years or so and clear out the saplings and debris, without hurting the mature pines with their lower branches well above the flames.

My snowmobile coasted to a halt in the unbroken snow. Game and Fish Habitat Specialist John Goodwin roared up beside me, then cut his engine.

The silence crashed in upon us, like a crested wave signaling a shift in the tide. The forest loomed all around, dark, snow-dusted pine sentinels who have stood their ground impassively for centuries, linchpins of a complex living net of plants and animals bound by mutual need and dependence.

Faintly among the brooding trees, the wind carried a haunting screech.

“Goshawk?” I asked, hopefully.

Goodwin peered toward the silent trees, remote and perfect as the memory of love lost.

“Nope,” he concluded at last. “red-tail.”

We sat awhile in silence, savoring its texture, smooth as the borders of sleep. I looked along the margins of the snowed-over logging road. Just ahead, the turkey tracks were precise. So were the shadowing coyote tracks. They both emerged for a moment onto the open space of the road before disappearing once more into the sheltering depths of the inscrutable forest, each intent on their ancient dance of being.

Then we fired up the raucous engines of the snowmobiles and set off once again for one of the few remaining patches of true, old-growth ponderosa pine forest in Arizona, an ancient gathering of trees on the north rim of the Grand Canyon dubbed Fire Point. It was the climax of a months-long effort to grasp the wonderful interactions of plants and wildlife in the state’s unique, old-growth ponderosa pine forests.

A delicate balance

Thanks to the tutoring of people like Goodwin, I’d learned a lot about the delicate balances which embrace squirrels, goshawks, mushrooms, black bears, pine beetles, woodpeckers and brown creepers.

Enter the circle anywhere.

Start at the roots.

Pines and firs all depend to some degree for water and minerals on mushroom-sprouting fungi which colonize their roots — a different species of fungi grows on each type of tree.

A clever fungus

The fungi, in turn, depend heavily on squirrels to spread their spores from tree to tree. The squirrels eagerly seek out the fungi truffles, which they can detect by their scent beneath a foot of snow.

The fungi, in turn, provide the squirrels with a rich food source during crucial times of the year, according to Jack States, a professor of forestry at NAU.

But the trees pay a price for the diligence of the squirrels, since the rodents live mostly on pine cone seeds. In some years, they eat most of the cone crop, and the tips of branches.

Then again, the squirrels who remain active all winter thanks to the cones and fungi are a lunch-hour blessing for the goshawks, foxes, bobcats and other denizens of the deep forest.

In the lower-altitude ponderosa pine forest, the Abert’s squirrel plays this crucial role.

In the colder mixed conifer forests, the red squirrel serves the same function. They cope with the colder winters by building and stocking middens, piles of sticks in the lee of a fallen log where they hoard cones.

Making much of middens

The middens must have just the right temperature and humidity to keep the pine cones from drying out or sprouting, which means the squirrels need dense forests in which the interlocking branches of the trees filter out much of the sunlight.

Such a closed forest canopy cools the forest floor in the summer and hoards escaping, nighttime heat in the winter.

So, the squirrels both need and sustain the trees.

Moreover, the large-scale distribution of trees affects virtually every creature in the forest.

Before Europeans arrived, the ponderosa pine forests were open and “park like” according to the journals of the early travelers. Often, they would ride at a gallop through grasslands that brushed the bellies of their horses — easily passing among stands of giant, 800-year-old ponderosas. Even currently living Rim Country old-timers can remember riding at a gallop through the forest, the lower branches of the big trees sprouting safely above the head of a horseman.

Even when she was a girl, recalls Gila County Supervisor Tommie Martin, the forest was far more open and dozens of now-dry streams ran down off the Rim.

Streams have gone dry

Those streams have gone dry mostly because the thickets of trees on the Rim compete fiercely for the available moisture, preventing as much water as possible from escaping into the streams.

In that now-vanished landscape, fires burned through every five years or so, helped along by brush fires intentionally set by Native Americans to maintain the open setting. The ash from the fires enriched the soil, the grasses came back quickly and the frequent burns prevented thickets of saplings from giving ing the fire a ladder to climb into the lower branches of the big trees. Once a big fire did clear out an area, different trees like aspen would quickly fill in the gap — until eventually overshadowed by the return of the big pines.

Such low-intensity fires created a patchwork that included open meadows, stands of aspen and mature pines. That patchwork created a diversity that sustained a great variety of wildlife.

Researchers have documented many of the effects of the current, crowded forest on wildlife — and the surprising benefits of wildfires, so long as they don’t burn so hot as to sterilize the soil and leave it unable to absorb water normally.

For instance, elk need meadows. While deer mostly browse on brush, elk chow down on grass to sustain their great bulk.

Elk need meadows

One long-term study along Highway 260 beyond Star Valley found that the distribution of meadows controls elk movements. The elk crossed the highway mostly to reach the larger meadows, which helped engineers design elk crossings.

In old-growth forests, fires created a natural mosaic of aspens, pines, oaks and meadows. Now, dense stands of ponderosa pine saplings, often at densities of 1,000 per acre, have choked out almost all competitors — setting the stage for a potential disaster. Both meadows and aspen groves have declined drastically.

Even dead trees vital

The cycle of interdependence between wildlife and big trees persists even after the trees die.

Consider the life of a dead snag, an unexpectedly vital part of a forest ecosystem.

Dead trees can remain standing for half a century, slowly decomposing under the assault of wind, rain and frost. Those slow changes provide a bonanza of ecological niches. Some studies suggest that 80 percent of the bird activity is centered around the mature, yellow-belly pines and the snags.

Old trees and snags attract a host of insects, including many varieties of pine beetles. Normally, that’s actually a boon to wildlife diversity, since the insects produce both food and dead snags needed by other animals.

Pine beetles run amuck

The pine beetles normally focus on trees whose defenses have started to falter. The first colonizing beetles emit a chemical signal, which draws other beetles. Rapid-fire generations of pine beetles chew large chambers in the inner bark and introduce a fungus that hinders the movement of water from the roots. That cripples the tree’s chemical counter-attack. As more and more beetles colonize the tree, the centuries-old lord of the forest slowly starves to death.

That triggers several, interlocking changes.

Birds flock to the tree, led by the woodpeckers with beaks tough enough to dig out the hidden insects. Those tough-beaked birds also hollow out nests in the decaying heartwood of the doomed tree.

Everyone loves a cavity nest

These primary cavity nesters raise their young in these protected chambers. But they abandon their carefully constructed cavities after a single nesting season to avoid a build-up of mites, parasites and diseases.

That leaves the hole free for colonization by a host of secondary cavity nesters, like the pygmy nuthatch, an endearing little chirp of a bird with no neck, a sub of a tail, and a voracious appetite for insects. Nuthatches flit through the forest and hop up and down the immense expanse of trunk, peeping incessantly, and gobbling up insects.

They’re one of the few species of birds which stays all winter. Their secret lies in jamming into abandoned woodpecker nests with dozens of hot little bodies, like so many college students stuffed into a phone booth.

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

Gotta love a good snag

“I just love a good snag,” gushed Goodwin, who now measures the quality of the habitat by the number of skeletal trees imploring the sky. “They’re beautiful. Just beautiful. But we often get people who say, we ought to get rid of those dead trees.”

We have in recent years glimpsed what happens when we critically disrupt those relationships.

The devastating bark beetle outbreak offers one sobering cautionary tale.

When bark beetles go bad

Bark beetles occur naturally in the ponderosa pine forests, but normally do little damage. The beetles and the pines have a long relationship, although the pine doesn’t get much out of the transaction — unlike the impact of the squirrels on its roots.

The trees produce defensive chemicals called terpins to stave off the beetles. The flying beetles can apparently detect the terpin levels when they encounter a tree. If a tree is stressed by drought, the beetles sense weakness.

So a beetle looking for a home will land on a faltering tree and chew into the layer which carries most of the nutrients up to the branches and out to the leaves. The beetles put out pheromones to signal the tree’s weakness to other passing beetles — then bores out chambers for its eggs and larva. The grub-like young feast on the tree’s vital inner layer. Once the beetle population has reached a certain level, the beetles put out chemical signals that warn-off newcomers.

Picking off the weaklings

In a healthy forest, the beetles merely pick off the weakened trees, producing useful snags in the process.

However, in recent years, bark beetle infestations have soared out of control, perhaps reflecting both the growth of tree thickets and the impact of the drought.

The dehydrated trees can’t produce the sap needed to fend off attacks. Moreover, although the beetles can fly two miles looking for a likely tree — they prefer to move as short a distance as possible — which makes dense forests more vulnerable.

Moreover, the mild winters produced by the drought have made it easier for the beetles to survive the winter and enable them to produce three to six generations per year, instead of one or two.

Millions of trees fall victim

To understand how unnatural forest conditions have become across millions of acres, you have to search out those last few stands of old-growth forest — like the gigantic pines in Grand Canyon National Park.

My forest guide and I sputtered through 25 miles of majestic, towering trees en route to Fire Point. Alongside the track, I noted deer, turkey, coyote and fox tracks.

During the occasional stops, we strolled into the looming forest to look for the peeled pine branch tips left by Abert’s squirrels, noted the tracks of one early-rising black bear, followed the rodent scampers, paused over the scrapes in the snow that marked a bobcat’s pounce on a rabbit, counted the pygmy nuthatches, and searched for spotted owls.

Then we crossed over the boundary into the Grand Canyon National Park at Fire Point.

Letting the forest burn

A few years ago, Fire Point caught fire. The Park Service let it burn. The flames crept through the grove of trees that were already giants the winter George Washington took office.

The fire left few marks, beyond some fresh “cat’s ear” scars on the trunks of big trees.

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.

Then I wandered across the snow, looking for tracks, my awareness for the moment was arched, and airy, and indefinite as the upward thrust of the ancient giants who loomed above me.

I came to the edge of the world. The multi-hued canyon dropped away at my feet, a 2-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 the circling red-tail from one of his 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.


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