Scientists study as life emerges in land under Mount St. Helens Beetles are followed by parachute spiders, plants, trees and elk

October 04, 1998|By KNIGHT RIDDER/TRIBUNE

SEATTLE -- A veneer of wax on the bodies of pioneer beetles resisted the drying power of ash that in a searing landscape like Mount St. Helens' can spell quick death for less hardy insects.

The carabid's small size made it easy for the scavenging beetle to dart under pumice pebbles to escape the sun.

Other post-eruption pioneers -- who became beetle food -- came in via parachute, riding the wind for miles to enter the mountain's barren waste land.

As new vegetation began to take hold, the insect Adams and Eves mysteriously died. But after their deaths, they filtered nutrients into the sand-like ash, creating pockets of compost where seeds could flourish.

After the volcano erupted on May 18, 1980, killing 57 people, choking the Columbia River with debris and obliterating 150,000 forested acres, various research projects have looked at the recovery of trees, fish, birds and animals small and large.

Scientists such as John Edwards have turned their attention to the tiniest of affected organisms, predatory beetles, ballooning spiders and other early arriving bugs that helped in greening the devastated acreage.

According to island biogeography theory, "as organisms colonize new island, the rate of addition of new species will eventually decline until extinctions equal arrivals and an equilibrium is achieved," Edwards, a University of Washington zoology professor, wrote in a yet-to-be-published book about the impact of volcanic eruptions on the environment.

Volcanoes "are, in effect, ecological islands and are thus ideal subjects for the test of island biogeographic theory, especially where repeated eruptions wipe the slate and a replay of the successional saga begins again."

Meanwhile, the greening of the volcano continues, studied from the Mount St. Helens National Volcanic Monument, where nature has largely been left to heal on its own, and on nearby Weyerhaeuser property where recovery has been given a few nudges.

In both locales, insects and animals have been active in helping to change the landscape's face.

From 1981 to 1986, ballooning spiders made up nearly one-quarter of insects that moved into the blast zone from nearby farmland, forests and logging areas to become food for others, Edwards said.

Some of the insects, such as grasshoppers, died in the hostile conditions, and their bodies were scavenged for meals. Beetles were seen eating other insects, including aphids and midges.

By 1985, there were measurable nutrients in what was formerly barren ash -- an increase that could have derived only from the decaying bodies of immigrant insects, Edwards wrote. But it's ,, unclear why the pioneers succumbed upon the arrival of conditions favorable to other animals.

"There is an unexplained, almost paradoxical relationship," Edwards said. "The pioneer beetles that can tolerate very harsh conditions do not co-exist with later colonists when plants have arrived on the scene. It may be they have some special adaptations to life on bare ground, but are out-competed when there are plants around."

Burrowing northern pocket gophers were survivors from minute one, thanks to a life-saving subterranean lifestyle. They and 13 other small mammal species escaped instant incineration. And the gophers pushed rich mineral soil up into the ash layer as

they burrowed, making it available for plants such as fireweed to lodge their seeds.

The ash proved to be a surprisingly good mulch that in the first two or three years of recovery held moisture in the ground for plants and helped suppress weed growth in replanted forests.

"So the vegetation that did come back was very, very healthy and for the most part was bigger, taller than the usual average height for the vegetation of that area," said Ross Gilchrist, Weyerhaeuser Longview timberlands administrator.

Early on, the timber company experimented with planting trees DTC straight into the more than 60 percent silica ash. But the pulverized rock offered as much nutrients to pines as beach sand, Gilchrist said.

The company then decided to "scalp" away ash to expose mineral soil to replant 11 million Douglas fir, 7 million Noble fir and 180,000 cottonwoods along major streams, said Dick Ford, former forest manager. At extreme ridge tops where soils were shallow and east winds dry, Weyerhaeuser planted 50,000 lodge pole pines, which do well in desert-like conditions.

Roosevelt elk, lured back to the blast zone by grasses and clover, actively shaped that landscape.

The elk have doubled to an estimated herd of 3,000. And elk, which rub against trees to clean off the velvet that covers their antlers, prefer that type of pine, said Ford, now director of Weyerhaeuser's Forest Learning Center: "They have maimed and killed most of those lodge pole pines."

The grazing species' initially explosive calving rates are reversing. Now, as the young trees have matured, blocking light the grasses need to flourish, calving rates are lower and winter kill rates higher.

Outside the monument, a multiagency project since 1994 has looked at whether thinning Douglas firs might diversify the wildlife that call the forest home.

Right now, much of the wildlife living space is sky high, as if all the books were piled on just the top shelf, said Peter Frenzen, monument scientist. If that uniform "umbrella" instead had gaps that allowed light to seep through, could you create a mosaic of trees and bushes of different heights, each foliage layer offering habitat to distinct species?

Species such as the northern flying squirrel and the spotted owl specialize in specific types of forest. Could you re-create those conditions to encourage their survival? Finding the answer could take decades.

"The jury is still way out on that stuff," Frenzen said. "All that the biologists know is these suite of organisms have developed in those conditions. Now, by creating them artificially, can you do them any good? We don't know."

Pub Date: 10/04/98

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