MOUNT ST. HELENS — The rainbow trout flexed and flopped as Charlie Crisafulli scraped a few scales from its side with a knife.

"The fish are very large this year," he said, before releasing the 5-pounder back to its watery home.

When Crisafulli first ventured onto the moonscape left behind by Mount St. Helens' May 18, 1980, eruption, Spirit Lake was lifeless. His discovery of a single lupine growing near its shores two years later was cause for wonder.

Now, as the U.S. Forest Service ecologist begins his 25th season on the volcano's flanks, thickets of trees shelter a growing number of animals and the lake supports abundant frog, salamander and fish populations.

The scales from the trout — and many more like it — will reveal the animals' ages. Biologists in snorkel gear will swim transects in the lake's shallows, counting fish and searching out the gelatinous egg sacs of amphibians.

The riotous return of life to the mountain upsets conventional notions about the way nature heals its wounds and offers blueprints for repairing damage done by man.

But much of the insight about St. Helens' recovery has been parceled out in scientific papers that deal with little slices of the landscape, like the spread of beetles, or the way airborne seeds took root. The big picture is visible mainly to scientists like Crisafulli, who have made the mountain their life's work.

Now, he and two other researchers who were among the first to venture into the blast zone within months of the big eruption are extending the view to a wider audience. In a paper published in today's issue of the journal Science, they summarize 25 years of ecological change at the volcano. And in a book that will roll off the presses soon, they document the work of dozens of researchers who have taken advantage of one of the world's most unique natural laboratories.

"It's important to share this information," said Virginia Dale, an ecologist who started tracking plant death and rebirth within weeks of the 1980 blast. "It would also be great to inspire more people to get out there and do research."

The publications come at a time when Mount St. Helens' ecosystems are beginning to rebound more rapidly than ever before, said Dale, whose work has been paid for by National Geographic.

Willow trees in some spots top 20 feet, and are as densely packed as a jungle. Montane shrews, Pacific jumping mice and every other species of small mammal found in the Cascades have returned. The first Douglas fir trees to regrow are finally bearing cones this summer.

"Early on, frankly, we spent a lot of time monitoring plots where there wasn't a lot going on," said Dale, who now works for Oak Ridge National Laboratory in Tennessee. "Now we're at the stage where the dynamics are really changing quickly."

Richness begets richness

KEN LAMBERT / THE SEATTLE TIMES A noble fir rises between boulders near Spirit Lake.

The change is evident in a thicket of alder and willow so dense it will be impossible to see a person 10 feet away once the trees leaf out.

As Crisafulli approaches, he catalogues the bird songs he hears: yellow warbler, dark-eyed junco, white-crowned sparrow.

The thicket started out as small pockets of vegetation, nurtured by the presence of water and stable ground.

Throughout the 230 square miles devastated by the eruption, similar "hot spots" have served as the seeds for oases that are now beginning to reach critical mass.

"In many respects, we are at an ecological cusp right now," Crisafulli said.

As hot spots coalesce and spread, they create bigger, more durable refuges, where animals are less likely to be wiped out by a harsh winter or a single predator.

One of the first things biologists noticed as they tracked the recovery was that richness begets richness, Crisafulli said.

A single plant would attract insects and capture windblown seeds, leading to an increasing spiral of life. Spider webs on hummocky ground gathered enough moisture from the air to allow seeds to germinate.

The principle still holds true, and seems to be accelerating the boom in plant and animal life.

Stepping carefully on the moss-covered ground, Crisafulli points out a water-filled depression where elk cool off on hot days.

The little ponds left behind by the big mammals provide salamanders and frogs an ideal spot to lay their eggs.

Lessons learned

It's only with time that researchers have begun to recognize the broader patterns at work in the recovery, said Forest Service geologist Fred Swanson, who has studied the way the underlying mud, ash and debris flows shaped the distribution of new life.

He hopes a new generation of ecologists will continue to monitor those patterns, which could provide valuable tips for restoration projects — whether of naturally burned forests or riverbanks denuded by urban development.

"We really need to be thinking about the larger landscape level," Swanson said.

Lessons learned at Mount St. Helens about landscape recovery already have been widely applied.

The understanding that pockets of vegetation attract animals and other plants is embodied in federal and state forest-management plans that require timber companies to leave some trees standing, along with dead snags that harbor birds and insects.

Reclaimed strip mines in Wyoming reverted to natural shrub lands when planted with dense clusters of native plants such as sage brush, salt bush and bunch grass. In the past, miners would scatter seeds from exotic grasses and legumes, then wonder why the natural ecosystem never recovered.

At the Army's training ground in Fort Benning, Ga., Dale helped develop a program to protect the endangered red cockaded woodpecker and the longleaf pines it depends on for survival. Many of the plants that survived the furnace blast at Mount St. Helens have buds buried underground, as do young longleaf pines.

Based on that, the Army knows it can occasionally set fires to clear unwanted vegetation, allowing the forest to replenish itself and keeping habitat good for the woodpeckers.

Big trout thrive

KEN LAMBERT / THE SEATTLE TIMES U.S. Forest Service biologist Charlie Crisafulli releases a rainbow trout after measuring it at Spirit Lake.

Ecology textbooks used to present the succession of species as an orderly march, Dale said. Twenty-five years of observations on Mount St. Helens have revealed it as a surprisingly complex dance.

Before the 1980 eruption, Spirit Lake was the heart of a placid resort beloved by generations of Northwesterners. It was also typical of high-mountain lakes: The sparkling clear water contained so little fish food that the only way to maintain trout for anglers was annual stocking.

The eruption buried the former valley floor under 200 feet of debris, and red-hot avalanches of rock heated the water in the lake to 100 degrees, wiping out all fish.

Someone apparently smuggled a few trout back into the lake in the early 1990s. And since then, nature has taken the tale in an unexpected direction.

While trout rarely grow above a pound or two in most mountain lakes, Spirit Lake is now filled with thousands of 4- and 5-pounders, like the fish Crisafulli netted earlier this week.

In a cause-and-effect chain reminiscent of the old woman who swallowed a fly, the fish grow so big because they have more to eat; they have more to eat because the lake is now fringed with shallow areas where plants can grow; and the shallows were created by the volcanic mudslide that slopped into the basin.

But will the behemoths survive?

Some of Crisafulli's newest studies show that portions of the lake seem to be shifting back to the original, nutrient-poor conditions.

Whatever the outcome, Crisafulli hopes to document it.

"There are a lot more stories to be told here," he said.

Sandi Doughton: 206-464-2491 or sdoughton@seattletimes.com