“I would tell anyone to take their vacation in Yellowstone this year,” William Romme told me. “This is a natural event not to be missed.” The natural event he was talking about is the multitude of fires that have burned about 650,000 acres so far in Yellowstone National Park. Romme is a professor of biology at Fort Lewis College in Durango, Colorado, and he has spent ten years–five of them on a National Science Foundation grant–putting together a fire history of a section of central Yellowstone Park. Working with National Park Service research biologist Don Despain and crews of student helpers, Romme walked the park’s backcountry, eventually surveying about 15 percent of Yellowstone’s 2.2 million acres.

Most of Yellowstone’s forests–and most of what is burning this year–are lodgepole pine woods. This single species is so dominant that it often forms pure stands. The trees in each stand are all (or nearly all) the same age. Even-aged stands of lodgepole pine are products of fire. The flames kill the old trees, clearing the ground for a new generation.

Romme and Despain took core samples from selected trees in each stand. According to Despain, counting the rings in the core samples will give a date for the fire that is accurate within five to seven years. Fire scars are more precise evidence, so Romme and Despain looked for these with particular care. Fires often scorch trees without killing them. The trees enclose the burned areas in scar tissue and keep growing. Counting the rings back to where the cambium was killed can date a fire within a year or two.

Romme and Despain concluded that the woods in their study area were last hit with large and frequent fires in the period between 1850 and 1860. What Romme calls “enormous fires” swept through between 1700 and 1725.

So this summer’s fires, roughly 125 years after the last big ones, are about what we might expect in the last 25 years of the 20th century. This year, the driest year in memory, just happened to be the moment. Romme and Despain are cautious about giving reasons for the 100- to 150-year fire cycles. Dry weather is the likeliest cause.

In the years since the National Park Service began keeping records of naturally occurring fires, an average of 17 fires per year–almost all caused by lightning–have been reported. That average includes swings from as few as 2 fires a year to as many as 50. In just the past ten years, Despain told me, the year-to-year differences in both the number and size of fires have been very great. He calls 1979 “a good fire year. We had some big fires–or what we thought of as big fires before this year.” In 1981, several fires burned about 20,000 acres. But from 1981 through August of 1987, a time when every natural fire was allowed to burn, not a single blaze covered as much as an acre. This year, when no rain fell for two months, the fires began to spread.

Another explanation for fire cycles has been that they accord with the life cycle of a lodgepole pine forest, which has been believed to be a century to a century and a half. But Romme and Despain have discovered that the actual life cycle is much longer. It takes fuel to sustain a fire, and in cold, dry Yellowstone Park, it may take 400 years for a lodgepole pine forest to grow the fuel needed to burn it. The stands that grew from the fires of 1850 and the stands that grew from the enormous fires of 1700 are not the stands burning this year. These date from the 16th and 17th centuries.

This year’s fires in Yellowstone have become a matter of public controversy because of a National Park Service policy, instituted in 1972, to let naturally occurring wildfires burn unless some compelling reason–such as public safety–makes it necessary to extinguish them. Before 1972, the policy was to suppress all fires in the park.

Romme thinks that the fire suppression policy had almost no long-term effect. The policy existed on paper from the beginning of the Park Service administration of the land, but it wasn’t until the late 40s that the NIPS had the means to make it effective. Prior to World War II, fire fighters had to walk or ride horses into the backcountry, and the fire-fighting technology was quite primitive. In those years, rain quenched many more fires than the Park Service did.

After World War II, smoke jumpers and aerial spraying of chemical extinguishers made fire suppression feasible. By 1972, the forests of Yellowstone averaged a little older than they would have been without the policy, but otherwise, things hadn’t changed much. The fires of the past 16 years have begun reestablishing the old balance.

Editorial comment here and there has blasted the Park Service for its policy of letting the fires burn. Early last week the Chicago Tribune claimed that “damage to a treasured national park has been devastating” and accused the Park Service of having a “poetic” concept of nature.

Romme disagrees with this assessment. He thinks the policy is sound, that fire–even a lot of fire–is a natural process. Even if half the park burns this summer, there will still be lots of mature forests left. And he shares the Park Service’s poetic faith that the burned areas are not destroyed. Next spring, they will begin a process that will lead first to a new forest and then to a new fire.

Despain points out that this kind of year actually proves the soundness of the “let them burn” policy. The Park Service is required to keep the park in a state as close to natural as possible. Ecological studies showed that the natural state was a mixture of grasslands and forests. The forests ranged in age from a few centuries to a few years, and fire seemed to be the major ecological force that maintained the age range, that prevented Yellowstone from evolving into a uniformly mature forest. “Fire is just as important as rain and sunshine to the ecosystem of Yellowstone,” Despain told me.

If you want to attack that conclusion, your best evidence is the string of fireless years from 1982 through 1987. How can fires be so important if there aren’t any fires? But this year’s big blazes offer a convincing demonstration of the idea that fires will happen often enough and extensively enough to provide for the periodic renewal of the forests. They strongly support Despain’s reading of the ecosystem.

Both Romme and Despain regard accurate mapping of the fires as a priority project for next spring. Wildfires are not all-consuming holocausts. They burn one hillside so hot that every living thing, plant or animal, not safely underground is incinerated. The 40-acre slope next door may be untouched. Unburned patches are refuges for wildlife and seed sources for the plants that will eventually recolonize the burned ground. When we learn the exact extent of the burned land, we will almost certainly discover that the fires actually consumed much less acreage than this summer’s news stories would suggest. Despain cites preliminary–and admittedly sketchy–reports, based on flights over the burned ground, of 30 to 50 percent destruction. In other words, of the 650,000 acres within the boundaries of the various fires, something between 195,000 and 325,000 acres were actually burned. This would represent from 9 to 15 percent of the park’s total area.

If you visit the park during the next few years and walk or ride through the burned ground, you will be able to see the renewal the fires have brought. At first, the land will look like a prairie full of standing dead trees. But the grasses, sedges, and wildflowers are not prairie species. They are plants of the forest floor–yellow violet, heart-leaved arnica, glacier lily, and leafy aster–whose roots survived the fire.

The fireweed’s bright red blooms will be as numerous as Yellowstone’s 1,000 hungry moose will allow. Moose love fireweed, a plant that appears in huge numbers on fresh burns and declines sharply within a decade. Elk and deer will be eating elk sedge and Ross’ sedge. They ignore these plants most of the time, but the fire gives both sedges a shot of nutrients that makes them worth eating for a few years.

The standing dead trees will be resorts for woodpeckers, and especially black-backed and three-toed woodpeckers. These are fire birds, following the flames from place to place in search of standing dead trees to mine for insects. They will be more common than usual for the next few years. In a Yellowstone where all the forests were mature, these birds would be rare or absent.

The woodpeckers will dig nest holes, which will be taken over by mountain bluebirds and tree swallows. Both species use standing dead trees as nesting and perching sites, and both like wide-open spaces for feeding.

Change is slow in the cold, dry world of Yellowstone, where the growing season is short and blizzards can erupt in any month of the year. Lodgepole pine seeds will be germinating over the next five years–the nutrient-rich ash left by the fires is an ideal seedbed–but it will be 20 years before we notice the trees above the grasses, sedges, and wildflowers.

The next few decades will be a very good time to see elk at Yellowstone. Grassland becoming woodland is a prime habitat for them, and with so much more good land available, the herd will grow bigger and healthier.

A century from now, this year’s burnt-over ground will be a maturing pine forest. Animals of the old-growth forests–goshawks and pine martens–will move in. In three or four hundred years, the forest will have created enough fuel to consume itself, if a dry year makes conditions just right. Then the process will start over. Things seem to have been going on this way since the end of the Pleistocene.

The purest absurdity in the demand that we step in and suppress the fires is that fire fighters actually do far more damage than flames. Digging a firebreak involves scraping through humus to mineral soil. This brutal exercise strips away the topsoil and makes it very difficult for plants to get started. And in this cold, dry climate, the scar heals very slowly. It will still be visible as a barren strip of very sparse vegetation long after the lodgepole pine forest has matured and all other signs of the fire have vanished.

Over the long term, a policy of fire suppression would eliminate habitats for plants and animals adapted to young woods, and thus reduce the number of species in the park. And as more and more pine woods became highly flammable mature forests, the job of protecting them would become nightmarishly dangerous and extremely expensive.

If you have been to Yellowstone, I’m sure you have memories of beautiful places and sublime sights, but I would argue that the most beautiful thing about Yellowstone is its size: 2.2 million acres, more than 3,400 square miles, an area equal to two-thirds of Connecticut. And the park is almost surrounded by national forests and Grand Teton National Park, where there are several million acres more of wilderness or near-wilderness lands.

According to Romme, the “real purpose” of Yellowstone is to have a place that’s big enough and undisturbed enough to allow natural processes to run their course, a place where fires will start naturally and stop naturally. Here in the midwest we should be able to appreciate that idea. We have to set fires in our preserves. Our prairies and savannas are so small and scattered that their chances of burning naturally are almost nil. The most visionary prairie zealots in Illinois would never dare to imagine the wonder of a preserve so big that you could rely on nature to handle the burning.

This summer offered strong evidence for Romme’s view that Yellowstone is big enough to allow nature to both start and stop fires. Much land has already burned; more will probably burn before the first frost ends the fire season. But millions of acres of unburned forests remain, and next spring the rebirth is certain. More dry years may produce more fires in the park, but the burning is self-limiting. Only mature forests can burn, and the areas burned this year are now fire barriers that will prevent the spread of new blazes.

It is true that tourists have been inconvenienced, but visits to remote mountain wildernesses are not usually trouble-free. A road closed down by smoke is no different from a road closed by snow. Last August, a summer snowstorm closed roads in the park for two days. This year, fires closed them for somewhat longer. In another hundred years, fires may close them again. Nature is like that sometimes. Which is why it is more interesting than Disney World.

The Park Service will have to consider strategies for protecting populated areas. These could include deliberate, controlled burning of the woods around the few towns at the edge of the park.

The only mistake the Park Service made this year was in not letting the fire burn around Old Faithful. At Grant Village, another developed area in the park, the decision was made to protect only the buildings and let the fire have the surrounding forest. This worked. The woods burned, the buildings were saved, and Grant Village is now completely protected from fire for the next 300 years. At Old Faithful the forest was saved, so now endless caravans of tourists will continue driving through a tinderbox.

Looking over all that has happened in the past few months, Despain summed up his opinion of the policy to let the fires burn: “This is a good policy. Every hundred years or so, it gets expensive, but it is a good policy.”