OUT

F THE AS

by James R. Sedell, Jerry F. Franklin, and Frederick J. Swanson

Aquatic Ecologist, Chief Plant Ecologist, and Research Geologist, respectively, Pacific NorthwestForest and Range Experiment Station, U.S. Forest Service

Reprinted from AMERICAN FORESTS, October, 1980. Magazine of The American Forestry Association,1319 18th Street N.W., Washington, D.C. 20036

Even as the decapitated mountain threatensfurther devastation, scientists are observingthe ecosystem's remarkable powers of recoveryby James R. SedcII, Jerry F. Franklin, and Frederick J. SwansonAquatic Ecologist, Chief Plant Ecologist, and Research Geologist, respectively, Pacific NorthwestForestand Range Experiment Station, U.S. Forest Service

After a century of silence, Mt. St. Helens took just a few moments to transformmajor expanses of lush, green forest into ashen, gray wasteland. Yet, almostimmediately, green began showing through the ash.

The eruption began when a large earthquake triggered a catastrophic slump of thenorth side of the mountain. Millions of cubic yards of rock, ice, and snow rushed northand west, topping a 1,000-foot ridge, flowing down the valley of the Toutle River'sNorth Fork, and ripping up many square miles of big timber on the valley floor. Thismassive flow unroofed a zone of superheated ground water, which flashed to steam.

The resulting blast blew down timber like matchsticks over more than 100 squaremiles. Fragments of wood and foliage, mixed with pumice and pulverized rock, blank-eted the landscape to depths of four to 16 inches, and gave the appearance of graysnowfall. Beyond the shattered carcasses of timber, the hot blast scorched standingtrees and left a red ring of dying forests. A vertical blast. first of steam and then ofgases from within the volcano, shot 65,000 feet into the air and carried with itshattered rock, pumice, and car-size blocks of ice. Pyroclastic flows containing rockfragments and pumice hotter than 900°F boiled off the north face of the mountain.The landscape changed throughout the day, and is changing still, as further eruptiontriggers more debris flows and ash falls.

The sight of the devastation overwhelmed scientists and others who went to workin the area. But life is already returning to the land's resilient ecosystems. Overcenturies and millenia these ecosystems have experienced dramatic changeswrought by volcanism and wildfire. Over years and decades, the plants and animalshave recovered. What sets the events of 1980 apart is the large number of spec-tators looking over the mountain's shoulder.

Researchers from the Forest Service's Pacific Northwest Forest and RangeExperiment Station are enga ged in an immediate assessment of problems of soilstabilization, revegetation, stream cleanup, salvage of dead trees, reestablishmentof fisheries, and the effects of ashfall on water quality and quantity. The article thatfollows is based on the observations of the scientists as they began their work. Whatwe have seen so far—the power of the volcano and the recuperative powers of theecosystem—is impressive.

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Don Elder, USDA

VEGETATIONE

ven while the ash was still falling, the green of plant sur-vivors tinted the stark landscape. The volcano's blast killed

above-ground plant parts within its reach, but it failed tosterilize the soil. Plants sprouted from roots or rhizomes withindays or weeks. Fireweed proved well-adapted to poke upthrough the ash crust, and it soon colonized vigorously. Re-growth is particularly noticeable where erosion has removedpart or all of the ash and pumice mantle.

Each week, more diverse and vigorous growth of stream-side vegetation can be seen. Other wetlands, such as seepareas and marshes, are now visible as green patches. It is tooearly to know if this regrowth will suffer from erosion caused bywinter rains, but so far the vegetation has shown remarkableresilience. Areas covered with snow at the time of the eruptionare in particularly good shape. The snowpack protected smalltrees as well as shrubs and herbs. The snowpack slumped asit melted, breaking up the ash and pumice crust and providingavenues for plant growth. These sites began recoveringrapidly as a kind of instant forest emerged from the filthysnow.

Natural reseeding of the blast zone began in earnest in latesummer with arrival of the light seeds of fireweed, willows, andother plants. By summer's end, many plants were sprouting,including just about all the original shrubs and herbs—fromferns and trilliums to huckleberry. Some portions of the mud-flows in the lower Toutle and Muddy Rivers were colonizedby black cottonwood seedlings within weeks of the May 18eruption.

Don Elder, USDA

LANDSCAPEO

n the mountain's north slope, where the blast was cen-tered, a jumbled, unfamiliar landscape greeted re-

searchers. In the photo at right, a U.S. Geological Surveyhelicopter seems to perch at the edge of nothingness, havingferried to the mountain scientists who conducted seismicmonitoring. Farther downslope, debris flows on the NorthFork of the Toutle River buried forests and floodplain withdeposits hundreds of feet thick, and formed an eeriemoonscape of spires, pits, and gullies. New lakes formedwhere the debris dammed stream channels. An entirely newdrainage network is forming on the surface of the pyroclasticand debris flows. But streams changed by mudflows are be-ginning to cut back into their original channels.

Erosion in the form of small landslides and gullies beganeven in the first days after the initial eruption. This fall andwinter, heavy rains will move vast quantities of ash and debrisdown hillsides and into stream channels. The ash depositseliminate habitat for aquatic organisms. But high stream flowswill erode these deposits and permit biological recovery. Asthe ash and debris are washed from slopes, the original soil isbared, and roots remaining below can resprout. The land isfurther enriched by volcanic fallout, which is literally droppingnew soil from the sky.

Tracks of elk, deer, coyotes, and other large animals werevisible immediately after the eruption. Many survived the blastto emerge and wander in search of scarce forage. Insects andother invertebrates are the most conspicuous animal life.Foraging ants are a noticeable feature of the landscape, butshortages of food and water are taking a heavy toll. Hornets,flies, spiders—and many, many mosquitoes—are frequentlyencountered. Pocket gophers, moles, and probably other bur-rowing vertebrates also survived in significant numbers. Birdsare least in evidence of all the animals relative to their numbersbefore the blast.

S. Greene

FOREST

STREAMS, LAKESConditions at the edge of the blast zone vary, depending on

the lay of the land in any given area and its distance fromthe mountain. Brown stands of scorched, standing dead treesoccupy thousands of acres to the northwest on lands of theWeyerhaeuser Company and Washington Department ofNatural Resources. To the north and east, the transition fromblasted, down timber to green stands occurs over a lineardistance of only 400 or 500 feet. Enormous toppled Douglas-firs made scientific forays physically difficult in some areas. Inthe photo above, coauthor Jim Sedell scrambles to gatherdata on Ryan Lake.

Airfall ash coats standing trees and clings tenaciously tofoliage. Rain and wind remove only part of the ash. Much of thefoliage is seriously damaged, although it is not yet clear if thiswas caused by heat, chemicals, or the ash coating. Fortu-nately, buds were not damaged. Buds had not yet burst openin mid-to-high elevations at the time of the May and Juneeruptions, and subsequent foliage appears healthy. But treesat lower elevations were further along in growth, and sufferedsevere damage to new as well as old foliage. Growth will beslowed until new needles are created, but mortality of theaffected trees will probably be limited.

Natural seeding of Sitka spruce and red alder, as well as of afew conifers, will come in the fall. But natural reestablishmentof dense forest stands in the core of the blast area will takemany decades—natural seed is scarce. Artificial reforestationcan speed the process where forest management is wanted.

T he streams and rivers that drained Mt. St. Helens before theeruption were clear, cold, turbulent waters that cascaded

over moss-covered boulders and large down trees. A richdiversity of aquatic organisms inhabited these flowing waters,which made them popular with fishermen.

The streams that received debris and pyroclastic flows werecooked or buried, or both. The little remaining surface waterflowed in several small, shallow channels, most of which hug-ged the margins of the valley floor. Floating pumice pebblesand fragmented organic material turned the once-clear watersinto a brown-gray soup rich in dissolved organic matter. Novisible life remained. But within two weeks, filamentous bac-teria and algae could be seen growing along margins of chan-nels and backwaters of streams draining the debris flow of theNorth Toutle River. These microbial algal mats thrived on dis-solved nutrients that leached from shattered rocks and trees.

Downstream of the debris flow, massive mud flows filled theriver channels. The North Toutle River mudflow raced 45 milesdown to the Cowlitz River and on to the Columbia. The tem-perature of the Cowlitz where it entered the Columbia was90°F, killing nearly all life in the channels. One month after theMay 18 eruption, the waters were still so turbid that an adultsalmon could survive for only four hours before suspendedsediment shredded its gills.

Many streams draining the blast zone have headwatershigh on Mt. St. Helens and other peaks to the north. The forestthere was blown down, and blast deposits containing organic

matter filled the channels up to 10 feetdeep. A few remaining organisms re-treated to crevices in the bark and woodof downed and shattered trees in thestream bed. There they fed primarily onbacteria and fungi.

Streams affected by debris flow tend totake slow, tortuous routes, and can nur-ture life more easily than streams hit bymudflows, whose waters are swift andturbid. Biological recovery will begin toappear in channel margins and backwat-ers of these mudflow streams, wherethere is less suspended sediment to scourthe bed and cloud the waters.

In streams suffocated by ash, theabundance and diversity of aquatic or-ganisms will be low until the ash has beenwashed to streamside or out to sea. Inver-tebrate communities in those streamsconsist of very small midges, a few cad-disflies, and stoneflies. The spawninggrounds and rearing pools of the salmonhave been buried by ash. But the watersof the Toutle River should maintainhealthy runs of salmon and steelheadtrout within a decade, so long as there areno significant eruptions in the future.

Tributary streams that flow into ash-laden rivers have provided major refugesfor fish outside the blast zone. The otherprincipal fish refuges are the small, newlyformed lakes where mudflows havedammed tributaries. These lakes serve assettling basins for ash, and downed treesand shrubs provide abundant cover.

Most of the conditions we have de-scribed so far are in areas west of Mt. St.Helens and her sister Cascade peaks.East of the crest, streams were affecteddifferently. Streams on the east side thatreceived heavy ashfall have maintained

comparatively intact communities of in-sects and fish in the salmon family. Thefish show signs of gill abrasion, but aresurviving. Habitats for rearing fish stillexist. Recovery should be rapid in theseareas. Survival through the first winter willbe particularly important for the recoveryof aquatic communities.

Mt. St. Helens' eruptions affected lakesand streams in a way different from otherwell-studied lakes and streams affectedby volcanoes in Russia, Japan, andAlaska. This is because of the rich forestthat had stood on St. Helens' slopes andbeyond. The volcano's blast blew tre-mendous quantities of organic matter intowater bodies, resulting in high concen-trations of dissolved material leachedfrom shattered foliage and wood. Thelakes have 20 to 200 times the levels ofdissolved organic nutrients that they hadbefore the eruptions. All the water bodieshave 20 to 100 times as much downedwood along their shores. Streams aredaily transporting hundreds of tons offoliage, bark, and wood fragments into theColumbia River estuary.

More than 30 lakes were directly af-fected by the blast. Lake waters wereonce low in nutrients and were crystal-clear and blue. Now they are black, cloudygreen, or brown—depending on size anddistance from the mountain. Spirit Lake,once a beautiful forest lake close to Mt. St.Helens, is stained black from the mate-rials leached by distillation of tree partsand foliage. Lakes within the blast zoneare murky brown from ash, blast deposits,and foliage leachates. Those in the ashfallarea are greenish from lignt reflecting offsuspended ash.

Biological recovery of Spirit Lake and

the newly formed lakes has begun fromscratch. These lakes, filled with debris,could be described as "primordial soup."A foul odor from burning wood, turpentine,and sulfur rises from Spirit Lake. Mi-croorganisms flourish as large pop-ulations of bacteria, algae, and proto-zoans feed upon each other and upon therich reservoir of dissolved nutrients. Mos-quitoes are rapidly colonizing the lakes.The biological activity is rapid and con-stantly changing as one group of mi-crobes exhausts certain nutrients and issucceeded by another group, which feedson the available food resources. Thebiological production of Spirit Lake hasnever been higher—although it has thusfar been limited to single-cell organisms.The small ponds on the debris flow of theNorth Toutle River changed color in a fewdays from murky green to red brown asdifferent algal and bacterial flora took over.

Lakes within the area of blown-downtimber are dominated by filamentous andspiral bacteria, but they also contain adiverse set of plant and animal com-munities. Bacteria, zoopiankton, andbenthic or bottom-dwelling animals canbe found, as well as salamanders andcrayfish. Considering the physical dam-age to surrounding forests, the aquaticcommunities are surprisingly intact.Hellgrammites and stoneflies emergedwithin weeks of the eruption, and are nownumerous. The bottoms of the lakes,which are now devoid of oxygen, will prob-ably recover and sustain a fish popula-tion in two to three years. In areas ofheavy ashfall, there appears to be a dropin the amount of algae. Fish growtn will beslow tnis year, but production of fish mayincrease within two to three years. ■