The Next Species: The Future of Evolution in the Aftermath of Man (21 page)

The explosion toppled most of the trees in an area called the “blowdown zone” that stretched north over 143 square miles; the trees now on the ground all pointed away from the blast like fallen soldiers. Trees at the edge of that zone were scorched and killed by the flow of superheated rock and gas that shot from the volcano’s mouth at 125 miles (200 kilometers) per hour, searing the landscape
with material up to 1,200 degrees Fahrenheit (650 degrees Celsius). It created a barren plane of pumice up to 131 feet (40 meters) thick stretching out six miles to the north.

Most of the lands in the blast area were on private or forest service property and were therefore part of an extensive salvage logging operation that had the forest replanted and growing within five years. But that wasn’t the case on the 110,000-acre Mount St. Helens Volcanic Monument established by the US Congress in 1982 to follow the natural return of the forest from the eruption. Researchers claim that Mount St. Helens is today the
most studied volcano in the world.

I visited the park ten years after the eruption and spent most of my time chasing several herds of elk, trying to get pictures of the species’ return to the area. Grasses and smaller plants had moved into the vacancies created by the fires that followed the blast. Elk from outside the park moved in and took advantage of these shoots even if they were buried under ash.

More recently, the monument celebrated its thirtieth anniversary, and monument biologists and geologists are recording nature’s process of renewal. Wildlife had a couple of breaks at 8:32 a.m. on May 18, 1980, that sped the recovery. Spring had come to the mountain late that year, so there were snowdrifts on the ground that protected the brush and plants of the forest and the animals beneath them. Lakes were still frozen and many fish and amphibians survived intact under the ice. Since this all occurred in spring, migratory birds as well as the salmon had yet to return. Nocturnal animals had already bedded down by the time of the explosion, some in burrows, and they fared far better than their wide-awake neighbors who were up at the crack of dawn.

Plants started to return in the first few years, their seeds emerging from the ash or carried in by reinvading animals. Wind has also played a key role in blowing in spiders, insects, and seeds. Prairie lupine, a mostly purple or blue wildflower with soft silvery green leaves, came back even on pumice within a couple of years. The plant, which fixes its own nitrogen from the air, created small microhabitats for
other plants. These plants trapped windblown debris and attracted insects, all of which ended up enriching the soil beneath them with organic matter.

New grasses and plants provided food for the birds, small animals, and larger plant eaters that followed. Ten years after the blast, the most common large animal species were elk, black-tailed deer, mountain goat, black bear, and cougar. The elk and the deer were most prevalent. Resident populations at the time of the blast that were too big to get out of the way or hide in burrows were cut down mercilessly. But open habitat created by the volcano and the fresh plants that emerged have attracted other populations of animals from outside the park back into its boundaries.

Plant colonization had occurred in boom-and-bust cycles. Single species rushed into areas that were free of competition—new grasses being the most dominant here at first. These grew explosively, but once predators, parasites, and competition returned, the newcomers tended to crash. Gradually though, more species established themselves and diversity returned. And with that diversity came stability as stable communities established themselves and the pace of succession slowed down.

When I visited the park thirty years later, the forest had revived in patches where trees were buried under snow or protected by rocks. The species makeup of the surviving forest had changed in spots. More shade-tolerant, understory trees like mountain hemlock had emerged to dominate the landscape where the taller Douglas fir trees would have grown before the eruption. The layer of ash that fell from the sky that day killed trees such as Pacific silver firs even years after the explosion.

However, conifers, the dominant trees in the Cascade Range where the volcano is located, had not returned in force. They were susceptible to drought and needed a certain type of fungus in the soil to help them grow. The succession of forest growth after fire or fiery volcano was a series of vegetation changes with brush or less stable trees coming in first, followed by more dominant, stable (what scientists
call “climax”) vegetation coming in last. Conifers, trees that bear cones—like Douglas fir, western hemlock, lodgepole pine, and Pacific silver fir—will dominate perhaps in the next few decades, but it will be hundreds of years before a true old-growth forest will reappear.

The eruption of Krakatoa, an Indonesian island between Sumatra and Java on August 27, 1883, is another example of nature’s propensity for destruction and renewal. It is often referred to as the first great natural catastrophe of the modern world, since telegraph wires had recently been laid across the oceans, and the
explosion became international news at the speed of electronic transmission.

The volcano had been sending up churning clouds of ash and pumice along with
explosive noises for almost two months. Villagers in the surrounding islands greeted these natural fanfares with near-festive activities. But no one was prepared for what came next: one of the largest eruptions in modern times.

The series of cataclysmic explosions began at midday on August 26 and lasted until the next day, ending with the grandest explosion of them all. On that second day, the northern two-thirds of the island collapsed beneath the sea, generating a series of huge eruptions, followed by a series of tsunamis that raced toward the surrounding islands. The waves lifted boats into the air and swept whole villages out to sea. The death toll was more than thirty-six thousand people.

A police chief on Rodriguez Island could hear the enormous bang of the volcano, “like naval gunfire,” though he was 2,970 miles (4,770 kilometers) away—the equivalent of someone in London, England, hearing an explosion in Baltimore, Maryland. The tower of ash and pumice rose to a height of nearly 30 miles (48 kilometers), raining down huge masses of pumice on the surrounding seas. Some islands of pumice were found later, floating in the water, laden with skeletons.

So
what has happened to the area since the eruption? The story is encouraging: within a century the remnants of Krakatoa, where not a blade of grass was visible for a year, were draped in tropical forest
from sea level to the 2,600-feet (800-meter) peak. There were now over four hundred species of plants, thousands of species of arthropods (spiders, crustaceans, and insects—including fifty-four species of butterflies), more than thirty species of birds, eighteen species of land mollusks, seventeen species of bats, and nine species of reptiles, many of which had to cross forty-four kilometers of sea water to even reach the islands. No species count exists prior to the eruption, but the numbers of animals challenges other counts in nearby areas.

Professor emeritus Ian Thornton of La Trobe University in Australia, who wrote many papers on the volcano, reported that Krakatoa offered “an optimistic lesson: That tropical rainforest ecosystems are capable of recovery from extreme, traumatic damage, if left alone and given time.”

To scale up from the aftermath of the eruption of Mount St. Helens or even the eruption of Krakatoa to the aftermath of the Permian extinction is an enormous leap. Still, some of the same principles apply.

The landscapes that existed at the Permian extinction were also barren. The Siberian Traps had spewed enough volcanic matter to cover an area the size of the continental United States. The coming together of all the continents into the supercontinent Pangaea had shut off ocean circulation, and life in the deep oceans began to lose oxygen. Stagnation started to replace moving currents and the result was the release of sulfur dioxide (SO
₂
), a deadly poison. The oceans had gone acidic, and shellfish and coral couldn’t grow hard shells. Unlike Mount St. Helens and Krakatoa, the buildup to the Permian extinction was not a singular eruption but a series of eruptions with consequences that lasted thousands of years.

The earth didn’t rebound rapidly. Early Triassic rocks are notoriously barren of fossils, making it hard, researchers claim, to get grad students to work them. Douglas Erwin, in his book
Extinction
, compares the earliest Triassic to the ravages of the Scythian hordes in
Prometheus Bound
: “This is the world’s limit that we have come to; this is the Scythian country, an untrodden desolation,” says Aeschylus.

The recovery, as at Mount St. Helens and Krakatoa, came from
survivors and immigrants that surrounded the catastrophe: the birds, fish, small mammals, and reptiles. The larger animals—the elk, deer, coyotes, and mountain lions that followed Mount St. Helens—came later. In the presence of a vacuum, evolution advanced the cause of life as it did with the spread and multiplication of new species of finches that first populated the Galápagos.

With the Permian extinction, the destruction was greater, and the recovery lasted longer. Douglas Erwin, paleobiologist at the Smithsonian, compares the Permian recovery to an empty chessboard where each square represented unique ecological niches. The empty spaces that followed the extinction presented different opportunities for life, for rapid speciation and expansion of individual territories. Those circumstances were more complicated than at Mount St. Helens or Krakatoa—whose eruptions did not lead to new species—since the Permian extinction led to
wholesale species changes, and it took ten million years (not one hundred years) for things to start coming back together.

For the Permian extinction, it wasn’t just a matter of animal species lost. Many of the rules that governed ecological relationships were abandoned. According to Erwin, the board collapsed entirely, and as the game resumed, it became “half chess, half backgammon, with some rules drawn from poker.” During the Permian, only one in ten snails or slugs was a predator. They made their living searching through the water and mud for organic debris. Some of them were grazers chewing on algae. But after the Permian extinction all that changed, as slugs and snails became vicious predators, many equipped with highly toxic poisons to capture prey.

The landscape of the first three million years of the Triassic was like a ghost town. The tiny fraction of species that were alive then was but a small portion of the species that thrived a few million years earlier, or
even a few million years later. Before the extinction, passive groups of animals dominated, but after the extinction, active groups took control. Sitting around, hoping your food would come to you, did not work as well as going out and getting it in this changed environment.

According to Smithsonian paleontologist Hans-Dieter Sues, the resurrection of the environment came in fits and starts. On land, the number of species lost was not as great as the loss in the oceans. Some species reappeared from refuges, safe havens for relic plants and animals. The tropics may have been such a safe haven.

An extreme example of these refuges can be found at
Fray Jorge National Park in northern Chile. Upon driving into the park, one can see only desert. This area receives less than six inches of rain a year, and the desert shrub is more suggestive of the badlands of the American Southwest than the lush landscapes of the Amazon. Yet perched atop the coastal mountains, some 1,500 to 2,000 feet (460 to 600 meters) above the level of the nearby Pacific Ocean, are patches of vibrant rain forest extending up to 30 acres (12 hectares) apiece. Trees stretch as much as 100 feet (30 meters) into the sky, with ferns, mosses, and bromeliads adorning their canopies. After leaving your car, you climb up an arid desert path and discover that it turns from dry desert shrub into forest. And then the biggest surprise: as you enter the forest it suddenly starts to rain.

This is not rain from clouds in the sky above but from fog dripping down from the canopies of trees—trees so efficient at snatching water out of the air that they get three-quarters of all the water they’ll ever need from the fog. That same fog at Fray Jorge also provides nutrients. Kathleen C. Weathers, a biogeochemist at the Cary Institute for Ecosystem Services, and her colleagues have discovered that this fog, originating offshore from some of the richest ocean waters on the planet, floats in bearing essential nitrogen and other chemical gifts. Similar bizarre sanctuaries may have safeguarded species during the Permian extinction.

During the early Triassic, most of the interior of Pangaea was a hot, dry desert. The continental plates that made Pangaea were fused
together, but as Pangaea finished its final assembly, the plates began to rip apart again. By the end of the Triassic, North America was pulling away from Europe and Africa as the crust between them sank, forming the Atlantic Ocean. Still, areas of the southern continents remained in tropical forest—safe havens, perhaps, like the fog forests of Chile.

But then species began to develop at greater rates than ever before. The first species attracted to the barren landscape of the early Triassic, as with Mount St. Helens and Krakatoa, were the weedy opportunists, “the ecological equivalent of dandelions springing up unbidden in a spring lawn,” writes Doug Erwin in
Extinction
. Though these “weeds” weren’t always plants, they acted like weeds in the sense that they moved into open territories and proliferated. The piñon pine forests of southern Utah bear the calcified remnants of the early Triassic scallop
Claraia
, a weedy species whose fossil shells today form pavements built from the remains of thousands and thousands of mollusks who thrived here when much of the western United States was covered with ocean.

Ferns were some of the first major colonists in other areas. They formed areas similar to the savannas or grasslands of today. Conifers were probably the first large trees of the Triassic. Most of the petrified trunks seen at Petrified Forest National Park in Arizona are conifers. They shared the landscape with tree ferns as well as ginkgos, which are related to conifers. The only member of the ginkgo genus that survives today is
Ginkgo biloba
, which has been used in Chinese herbal medicine for many centuries. The tree has fan-shaped leaves. The Japanese sometimes call it
I-cho
, “tree with leaves like a duck’s foot.”