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The onset of winter has ended the fire season in Yellowstone. The fire fighting crews borrowed from as far away as California have gone home. The controversies engendered by the National Park Service's so-called "let it burn" policy have cooled for the time being. They will heat up again when the new Congress convenes after the election. Hearings are promised. Various members of the Wyoming and Montana congressional delegations are hotter than the flames that almost incinerated the Old Faithful Lodge, and they will doubtless be looking for a chance to make headlines back home by skewering some bureaucrats.

Since the questions raised by the events in Yellowstone are of national importance, and since any changes in policy will be national, we all ought to understand what happened this summer, why it happened, and what the long-term effects will be.

We should start with a review of some facts that tended to get lost in the reporting from the fire zone. Thirteen major fires burned through Yellowstone this summer. Of these, only five were allowed to burn themselves out. The other eight were fought with every resource available from the moment they were detected.

Among the eight was the giant North Fork fire, which nearly incinerated Old Faithful Lodge. That fire started in the Targhee National Forest, which borders the southwestern corner of Yellowstone. The U.S. Forest Service tried to extinguish it there and couldn't. Once it spread to the park, the combined efforts of Forest Service, Park Service, military units, and fire fighting crews from all over the west could not contain it.

We need to realize how difficult it is to put out a forest fire. One fire ecologist I talked to, Carlton Britton of Texas Tech, claimed that he had only seen one fire in his career that was unequivocally extinguished by human effort. That one was a blaze that broke out in the middle of a logging operation in Arizona. Within seconds, 11 bulldozers were at the scene to cut firebreaks, and a few minutes later, converted B-17s began making passes--one every three minutes--to drop fire retardant chemicals on the flames. "Usually," Britton said, "they go out because the weather changes. It starts to rain, or the wind shifts."

Michael Scott, northern Rockies regional director for the Wilderness Society, agreed with that assessment. "They had 70 pumper trucks at Old Faithful Lodge," he told me. "But the only thing that saved the buildings was a last-minute wind shift that took the fire around them."

We should remember that fires burned all over the west this year, despite constant, massive fire-control efforts. Scott cited the Red Bench fire that broke out in a logging operation in the Flathead National Forest, just west of Glacier National Park. Within 12 hours, it had covered 5,000 acres. Within 36 hours, it had burned over 18,000 acres, and by 48 hours from its beginnings, it had scorched 37,000 acres.

In Yellowstone, the combination of drought, high winds, and old-growth forests rich in fuel made even the most massive control efforts futile. Winds in excess of 60 miles an hour blew burning debris more than a mile beyond the main front of the North Fork fire, and each piece of debris started yet another fire where it landed. Stopping a fire like that would require a firebreak more than a mile wide.

So most of the burning at Yellowstone would have happened regardless of anybody's policy, which means that the let-it-burn policy should not be judged on acreage incinerated in the summer of 1988. We can only evaluate the fire policy by examining its ecological effects.

Those effects appear to be wholly beneficial. In fact, my conversations with a number of fire ecologists, scientists who have devoted their careers to studying the effects of fire on natural systems, produced only one criticism of park policy. And that was a suggestion that the Park Service should have set fires in previous years in order to consume the fuel in old lodgepole pine stands--most of what burned this summer was lodgepole pine--and thus provide natural firebreaks. However, other ecologists thought that prescribed burning of this kind would not have worked in Yellowstone. To get some sense of the situation, we need to look at how lodgepole pine forests work.

One of the most intriguing aspects of nature is the way it confounds our comfortable habits of thought about good and evil, about what is harmful and what is helpful. In the radically simplified ecosystem of the modern farm, the corn borer is a wicked creature, totally harmful, and without redeeming qualities because it destroys corn plants.

But in the complexity of natural systems we find ambiguous creatures like Dendroctonus ponderose, the mountain pine beetle. Mountain pine beetles feed and breed in the phloem layers of the trunks of lodgepole pine trees. Phloem is conductive tissue that carries food from the needles to the rest of the tree, and a serious infestation of mountain pine beetles will intercept enough food to kill the tree.

Mountain pine beetles like big, healthy trees best, because the big, healthy trees have more phloem tissue and thus more beetle food. In mature lodgepole pine stands at lower altitudes, every tree in the stand may be infested, and 75 percent of the trees more than 16 inches in diameter may be killed over the course of an eight- to ten-year period. At higher altitudes, where the beetle is less common, infestations usually kill about one-third of the large trees. The old-growth lodgepole pine woods in Yellowstone were filled with standing dead timber killed by mountain pine beetles. The evidence seems plain, doesn't it? The mountain pine beetle must be the deadly enemy of the lodgepole pine. If something isn't done about it, the pines are doomed. The beetles will kill them all. But somehow that hasn't happened. Mountain pine beetles have been around as long as lodgepole pines yet thousands of square miles of our western mountains are covered with dense stands of lodgepole pine. Why? The answer lies in yet another of nature's ambiguous forces: fire. Fires need fuel, and mountain pine beetles provide that in abundance. In a single decade, a medium-level infestation creates 60 to 90 tons of dead wood per acre, enough fuel to feed a holocaust. And holocausts are just what lodgepole pines need to sustain themselves.

In the absence of fire, lodgepole pine may be replaced by the dense, stunted stands of spruce and fir that foresters call doghair stands. Or very modest numbers of young lodgepole pines may begin to grow--very slowly--in the shadow of the dead trunks that remain when the beetles finish their work.

Fires can renew the lodgepole pine woods, but their effects vary with the intensity of the blaze. Weak ground fires that burn at night or in wet conditions consume some of the duff--the mat of decaying pine needles and other stuff that covers the ground--but kill few standing trees. They may thin a pine stand somewhat, but otherwise they have little ecological effect.

Stronger fires, fires that spread to the crowns of most of the big trees and burn away nearly all the duff, kill most of the standing timber. Lodgepole pines produce cones that stay on the tree for up to 20 years, their seeds sealed by a resin that melts only when it is exposed to temperatures of about 120 degrees Fahrenheit. Moderate-intensity crown fires release tens of thousands of seeds per acre. The seeds fall on a bed of fresh, nutrient-rich ash lying directly on mineral soil, the ideal place for them.

The problem with this level of fire is that too many seeds fall. The young trees grow for a few years and then get so crowded that they stagnate and remain as a dense stand of stunted trees.

The hottest fires, the ones that not only incinerate the crowns of the trees but many seeds as well, are the best. Fewer seeds sprouting means a thinner stand, one where each tree will have room to grow. The hottest fires produce the healthiest young forests.

So when we look at the whole story, we see that the mountain pine beetle is not really the enemy of the lodgepole pine. The beetle creates the fuel that feeds the hot fire that creates the best conditions for a new lodgepole pine forest--which is incidentally the best habitat for new generations of mountain pine beetles.

Ecological processes like these, have been sustaining life in Yellowstone for thousands of years and allowing them to continue, encouraging them to continue when necessary, is the only way to keep the park in its natural state.

Wildlife is one of Yellowstone's major attractions, and many lovers of the park are concerned about what the fires will do to the animals. Certainly some small mammals and birds were killed directly by the flames, but their populations should recover quickly.

Predators should do well this winter because there is less cover for their prey. The winter figures to be a hard one for the hoofed animals, although the drought--which reduced plant growth to very low levels--will cause more privation than the fires.

A bad winter for elk, deer, bison, and bighorn sheep means a good spring for grizzly bears. The big bears rely on the carcasses of winter-killed ungulates as an early-spring food source.

Next year, populations of all the hoofed animals will start to grow and they will continue to climb for several years. Deer in particular will gain hundreds of thousands of acres of young forest habitat. Old-growth lodgepole pine woods are deserts from a deer's point of view.

We can learn much from what happened in Yellowstone this summer. A forest is a living thing that is born, grows old, and dies just like we do. Imagining that you can pickle a forest, freeze it in time, is as absurd as imagining that you can stay 25 forever. A wilderness like Yellowstone can show us the rhythms of nature, the long cycles of death and rebirth that endlessly renew life. We should be patient. As one ecologist told me, "I never saw a burn that looked good the next year, and I never saw one that looked bad a year later."

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