BOZEMAN, Mont. (AP) — On a plateau north of the Madison River, there are dense stands of dead lodgepole pine trees. Most are short. Interspersed among the thick toothpick stands are blank spots, having been nuked by a fire two years ago. Red stripes on the ground show where big logs burned hot enough to change the soil color, and sharp nubs poke a few inches through the ground.

John Cataldo, the park's fire management officer, stood before a group of about a dozen reporters in one of the blank spots last week, an expanse of dead lodgepole behind him serving as an illustration of Yellowstone's life cycles.

"Welcome to the Maple fire," Cataldo said. "And the North Fork fire."

The two fires, separated by 28 years, consumed the same ground. The North Fork fire burned more than 531,000 acres in 1988, Yellowstone's landmark fire season. The Maple fire ate a piece of that burn area in 2016, taking roughly 45,000 acres in what became the park's largest fire season since 1988.

Two fires burning in the same spot within a few decades isn't supposed to happen. Stands of lodgepole pine produce intense but infrequent fire — once every 250 to 500 years, said park ecologist Becky Smith. Burn scars are supposed to be fire barriers. Even a strong crown fire often slows and falls down once it reaches a semi-recent burn area.

The scars of 1988, which burned about 36 percent of the park, fit the mold. Fires could only penetrate it when they had strong winds or other abundant energy carrying it into the scar, Cataldo said. Then came the Maple fire, and with it a shift in the common understanding of the old fire scar.

"It was no longer necessarily a barrier to fire spread," Cataldo said. "It could actually carry a fire."

The action of 2016 is another paragraph in the epilogue of the 1988 fires. Since the iconic season, scientists have been watching the 30-year-old burn scars as the vegetation came back. They've had surprises, and they've had non-surprises. They talk about fire as a catalyst for the ecological processes that make the park work — it helps trees come back, for example — and now they've seen it return to the fire scar.

"The ecosystem just goes on," said Henry Shovic, a former Park Service soil scientist.

The continuation of the ecosystem doesn't mean it will always look the same, though. Among of the most surprising things park ecologist Roy Renkin found after 1988 was a resurgence of aspen trees. Renkin, who has worked in Yellowstone for nearly four decades, said the leafy trees with white trunks started showing up in brand new places in 1989, immediately following the fires.

"We reported it everywhere," Renkin said. "Exclusively in burned areas."

The appearance of aspen in the burn areas signaled that seeds had traveled and landed in new places, a unique occurrence for a species that has been in decline. It also signaled that the seeds had landed in favorable places, a remarkable feat because aspen germination requires a specific set of conditions — good soil, no competition from other plants and plenty of moisture.

Several other species returned easily as well, and the resurgence confirmed that the fires were just another piece of the ecological process, that the summer of constant firestorms wasn't a catastrophe.

"That's obvious now. It wasn't so obvious at the time," said Monica Turner, a scientist at the University of Wisconsin who does research in the park.

Lodgepole pine trees, the species that produced eye-popping crown fire, came back in varying thickness. The fire-adapted species is the predominant tree within Yellowstone. Becky Smith, a park ecologist, said 80 percent of the park's forests are primarily lodgepole pine.

Many lodgepole pines have serotinous cones, which release seeds when they burn. After 1988, regrowth density was highest where serotinous cones were most common.

Turner said there were some spots that saw as many as 200,000 trees per acre. Others were significantly less dense, showing the inconsistency in the number of serotinous cones.

"That was just something that we also didn't anticipate," Turner said.

One of the places where lodgepole returned in great density, Turner said, is between West Yellowstone and Madison Junction. Thick walls of trees can be seen along the road, most of them fairly short.

The recovery was similarly dense north of the river, where the Maple fire took off. But the existence of trees isn't what allowed the Maple fire to run — it was about what was underneath the trees and the weather.

Before the fire, the Maple fire burn area consisted of 28-year-old lodgepole pine trees standing over a bunch of dead logs. These logs are often referred to as thousand-hour fuels, and they are important in carrying fire in Yellowstone. They were especially dry in 2016, which helped the Maple fire progress.

"What did surprise me was how dry our thousand-hour fuels were, and how that's what was carrying the fire for several days," Smith said.

The fire presented an opportunity to learn about what parts of the 1988 fire scar might burn. Cataldo said areas with an abundance of dead logs are in play but extreme dryness would still be necessary for them to burn. He also said they don't know which areas have those conditions, and that they need to take a harder look at the 1988 burn scars.

The fire has also restarted the process that began there 30 years before. While standing in the burn area last week, Smith pointed out what was already back — shrubs, lupine, fireweed and a number of other species.

Cones still hanging onto dead lodgepoles were burst open, a gray piece of wood shaped like a blooming flower. The seeds had fallen somewhere below.

___

Information from: Bozeman Daily Chronicle, http://www.bozemandailychronicle.com