Life Returns to Mount St. Helens - University of Washingtonfaculty.washington.edu/moral/publications/1981 RDM NH small.pdf · Life Returns to Mount St. Helens One year after a major

Life Returns to Mount St. HelensOne year after a major eruption turned much of the mountain into an apparent grave,the slopes show abundant signs of resurrection

by Roger del Moral

Picking my way across a dry andbarren mudflow 5,000 feet up on theslopes of Mount St. Helens last Sep-tember, only four months after theeruption that devastated the mountainand far from any visible vegetation,I discovered an isolated, yet active,ant nest. These ants, probably f'or-mica subnuda, were at the top of afood chain whose lower levels, hiddenin the mudflow, were unknown. De-composing organisms and living plantsmay have formed the base of thechain, but without disturbing the nest,I could not determine whether soilanimals or fungi were involved. De-spite my curiosity, I decided that myignorance was less important than theexistence of this microcosmic ecosys-tem in a veritable desert. The antswere adding nutrients to the mud andhastening the reestablishment of lessad hoc food chains. After watching theactivities of these tiny survivors fora while, I continued up the slope,searching for signs of life among theruins of what was once the most per-fect of the Cascade volcanoes.

As Mount St. Helens marks the firstanniversary of its May I 8, 1980, erup-tion, it has already been exposed tomore hours of scientific scrutinv thanmost volcanoes are ever subjecled to.Logistical and technical problemsplagued efforts to study earlier erup-tions of other North American vol-canoes. Mount Katmai in Alaska. forexample, erupted in 1912, but ecolo-gist R. F. Griggs (to whom scientistsowe a major debt for his pioneeringbotanical and geologic studies of thatvolcano) was unable to approach themountain until 1916. By contrast. the

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proximity of Mount St. Helens to sci-entific centers provides a rare oppor-tunity to apply advanced methods incomprehensive, long-term studies ofhow ecosystems recover after a majorvolcanic eruption.

As an ecologist interested in com-Ray Atk6son

Above: Residents of Portland,Oregon, had a spectacular view ofthe July 22, 1980, eruption of MountSt. Helens, one of several sizableblasts that followed the majoreruption of May j,8. The mountain'sproximity to urban centers has beena boon to scientists. Right: Twomonths after the May 18 eruption, aparsley fern was found growing in aprotected area along a creek on theslope of the mountain. The fern,which survived a small mudflow, isgrowing out of a mud-coveredcrevice.

petition and succession in stressful en-vironments, I found myself among thehundreds of scientists drawn to themountain by the opportunity to doc-ument in detail the recovery processand by the exciting chance to testecological, evolutionary, and biogeo-graphical hypotheses. Biologists ob-serving events as they unfold onMount St. Helens are asking manyquestions: Which species first colonizethe various completely destroyed habi-tats? Are succession processes on to-tally denuded sites fundamentally dif-ferent from processes on sites witha residual biota? Does repeated ex-tinction and recolonization result inpopulations that are genetically dis-tinct from populations of the samespecies in stable habitats? Might com-munities whose species occur in pro-portions different from the regionalnorm be produOed?

My first field experience on the vol-cano after the eruption was on a re-connaissance trip last July with JerryFranklin of the U.S. Forest Serviceand several other biologists. While wewere awed by the magnitude of thedestruction, I was impressed even thenby the early evidence of biological re-coYery. Since that time, I have madeseveral research trips into variousparts of the volcano's "red zone" (theForest Service's designation for thepotentially most dangerous land, towhich access is closely controlled). Ihave also spoken with many other sci-entists investigating resurrection onthe mountain. The emerging pictureis one of diversity-diversity of impactand, consequently, of the conditionsto which organisms must adapt. Al-

Roger del Moral

titude and season influenced the na-ture and extent of the damage sufferedby different parts of the mountain.ln May, much of the landscape wasstill covered with snow. By contrast,when I visited the volcano late in thesummer of 1980 after a minor erup-tion, I found that hot-gas emissionshad scorched exposed plants. Thesewithered bits of straw provided an ink-ling of what might happen if a bigeruption occurred when there was nosnowpack to cushion the blow.

The May 18 eruption, like subse-quent smaller eruptions, was a seriesof events, each producing differentconditions. In some places, biotic re-covery has begun with survivors; inothers, colonizers from outside the im-pacted zone are required. Many eco-systems won't return to anything re-sembling their preeruption state foryears. But almost all affected ecosys-tems are showing resilience, and themessage is clear: while it took a beat-ing, life was never obliterated fromMount St. Helens.

The eruption, which followed twomonths of relatively minor volcanicactivity, unexpectedly concentratedits force on the land to the north.Although geologists had anticipateda major eruption and the magnitudeof the blast was not unprecedented,no one was prepared for the degreeof devastation spawned by the unusuallateral direction of the eruption. Morethan a cubic mile of ash was injectedinto the atmosphere, eventually coat-ing hundreds of square miles of forestand agricultural land. Millions of in-sects were knocked dead from the sky.Heat scorched trees up to sixteen milesnorth of the crater, and the blast blewdown trees in an arc of 160 degrees,extending more than ten miles fromthe crater. In most areas within a six-mile radius of the crater all life wasdestroyed. Large, rapid mudflows,confined to the lower elevations of sev-eral of the mountain's major streamsystems, crested over twenty-five feetand buried the flood plains of theMuddy River to the east and bothforks of the Toutle River to the west.A flow of hot debris then swept alllife from the northern flank of themountain and the upper Toutle Valley,creating an eerie moonscape. (Unlikethe sterile surface of the moon, how-ever, the debris is rich in organic re-siduals.) Melting glaciers and snow-fields triggered smaller mudflows onthe upper slopes. For example, on thesoutheast flank of the mountain. the

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melting of Shoestring Glacier causeda mudflow along Pine Creek that cov-ered vegetation on the edges of thecreek while removing it from the creekbed. In total, the eruption of MountSt. Helens had a profound impact ona region of about 160 square miles.

The number of animals killed asa direct result of the explosion washigh. Subterranean animals, such aspocket gophers, appear to have sur-vived in many places even within theblast zone, but mammals and birdsliving above ground had no protectionfrom the blast. The Washington De-partment of Game estimates thatamong the more prominent casualtieswere 5,200 elk, 6,000 black+aileddeer, 200 black bears, 11,000 hares,l5 mountain l ions, 300 bobcats,27,000 grouse, and 1,400 coyotes; theagency has estimated heavy additibnallosses due to ashfall. The eruption also

severely damaged twenty-six lakes bndkilled some eleven million fish, includ-ing trout and young salmon.

Animals outside the blasted areasmust contend with altered habitatsand reduced quantities and quality offood. [n the blowdown zone. elk anddeer are now common near water andwhere fresh forage has emerged fromthe ash. These survivors may have toforage more widely, but their reducednumbers w i l l ease compet i t ionstresses. Zoologists expect the popu-lations of vertebrates to build up asthe vegetation recovers, and they arehoping to determine how much thevertebrate pioneers may change theirbehavior with respect to habitat andresource use as their numbers in-crease. Significant changes in behav-ior would constitute evidence for in-terspecific competition, normally dif-ficult to observe in nature.

Larger vertebrates may form a cru-cial link in the process of vegetationrecolonization. Where heavy ash ormudflows dried to form a hard, uni-form crust. there are few cracks toshelter germinating seeds. But largeanimals wandering in search of foodor water make tracks that trap seedsand provide microsites suitably miti-gated for germination and growth.

Insects suffered incalculable tolls,primarily from the ash effects of theMay 18 eruption and from sizableblasts that occurred on May 25 andJune 12. Abrasion of the exoskeletonand ingestion of ash during preeningwere major causes of death. Studiesof agricultural areas in central Wash-ington have revealed that althoughhoneybees and other beneficial insectssuffered greatly, most insect popula-t ions recovered quickly. NearerMount St. Helens, where higher al-titudes mean a later spring, fewer in-sects were exposed at the time of theeruption. In the blowdown area, manyspecies have been encountered, butexcept near water, their numbers arereduced. I noted that seed set in lu-pines, which are dependent on insectsfor outcrossing (the production of off-spring from individuals of the samespecies but different strains), was pooreven where the vegetation received lit-tle damage. I believe this poor seedproduction was a result of the relativepaucity of pollinating insects.

Insect colonists will come frompools of insects outside the blast zone,and new insect communities will even-tually develop. Will these communi-ties be similar in species number andcomposition to communities in similar

but unaffected habitats? Daniel Sim-berloff's experiments during the1960s, in which all insects were re-moved from a series of very smallFlorida keys, indicate that such com-munities will soon return to the samenumber of species but that the com-position, largely a matter of chance,will be quite different. In the MountSt. Helens blast zone, the habitat islarger than in the island experimentsand there is no significant barrier tomigration. Will this alter the results?Will novel, stable assemblages of in-sects be formed?

Food limitations present survivinginsects and early immigrants withunique challenges. Species with themost generalized requirements arepredicted to be successful, and someearly observations in the blowdownarea support the idea that survivalrequires adaptability. In the weeksafter the big eruption, when ash wasubiquitous and aphids were rare, JerryFranklin and I observed a ladybug,normally an aphid predator, feedingdirectly on the sap of a bracken fern(Pter idium aqui l inum) that hademerged from the ash. Such short-circuited food chains should return tonormal as the vegetation, on whichaphids and other herbivores depend,recovers.

Because insects have short genera-tion times and are often early colo-nizers, entomologists are likely to ob-serve microevolutionary events, whichinvolve shifts in gene frequency ratherthan speciation. For example, wherebiotic recovery requires immigration,the first individuals of a species toinvade an area aie, not surprisingly,

Far left: Twelve miles or so west ofMount St. Helens (visible in thedistance), clear-cut and forestedareas along the North Fork of theToutle River escaped direct efectsofthe eruption. Large, rapidmudflows, however, buried theriver's flood plain. Left: Closer tothe volcano, trees were blown downand a hot debris flow, placed on topof the mudflow, swept all life fromthe upper Toutle Valley.

usually the best able to disperse. Re-duced competition and the absenceof predators in their new environmentmay permit a "founder effect" to oc-cur, that is, the genetic differencesbetween founding individuals and theaverage members of the donor pop-ulation become fixed. Such differ-ences will probably be minor, but ifthey occur repeatedly in many species,biogeographical processes that areknown to operate between islands willhave been shown to be significant forevolutionary processes in terrestrialsituations as well.

The effects of the eruption on vege-tation in various zones are also understudy: In forests within a few milesof the mountain, the initial ash de-posits fell wet because of eruption-induced thunderstorms and coveredthe trees and ground with a thick goo,which soon dried to form an imper-vious, cementlike layer. Ash on vege-tation interrupts gas exchange andcurtails photosynthesis. Jini Seymourof the University of Washington mea-sured temperature in ash-coated silverfirs (Abies amabilis) and found themto be more than 30oF warmer thanadjacent leaves from which the ashhad been removed. Fortunately, sinceheavy ash fell prior to bud burst inhigher elevations, much ash-free newgrowth is now present in most of thesurrounding forest. As ash-coveredleaves are washed clean by precipi-tation or replaced by new growth, conifer prodirctivity should return to nor-mal. Some species, such as red cedar(Thuja plicata), retain ash more te-naciously than others, such as Douglasfir (Pseudotsuga menzdesii), but

Eyewitness accounts, photographs, and instrumentrecords have been used to piece together the initialsequence of the May 18, 1980, eruption of Mount St.Helens, the youngest and most active Cascade volcano.A huge bulge formed rapidly, high on the north face ofthe mountain's volcanic cone, in the weeks prior to May18. Then, at 8:32 A.M. on that day, an earthquake struckthe mountain, triggering an avalanche on the north facethat is now thought to be the largest ever witnessed byhumans. Superheated groundwater close to the magmaflashed into steam, resulting in a lateral explosion thatpulverized rock and trees and sent a hurricane-force,hot-gas-propelled bolt of ash off the north face andacross the Toutle River Valley to the north and west.Temperatures in this iderno were estimated to exceed900" F. Comparable to a 400 megaton nuclear blast, theexplosion blew down trees in a l600 arc up to fourteenmiles north of the crater and totally devastated asomewhat smaller "blast zone." Seconds later, overlyingrocks were incorporated into a high-velocity debris flow,driven by rapidly melting glacial ice. On the westernflank of the mountain, this chocolate-colored massswept down the upper Toutle River Valley, eventuallyforming a mudfiow that swept the entire drainage area.To the north, a lobe of this hot debris flow crashed intoSpirit Lake while another swept over 5)}-foot-high

. THE ERUPTION

Coldwater Ridge, removing all lrft in its*path. As thesummit of the mountain collapsed, two vertical columnsof ash-laden gas and steam were injected more than65,000 feet into the air. This ash was eventuallydeposited, in layers up to fve inches thick, over 49percent of lVashington State and beyond. Close to themountain, ash deposits were less thick, but they fell wet,forming o sticky goo on all surfaces. The plume ofblasted ash also removed much of the remaining summitand lowered the peak from 9,677 feet to about 8,400feet. As a consequence, the feeding zone of all glaciershas disappeared. Shortly after these events andcontinuing throughout the next day, an indeterminatenumber of pyroclastic flows, or nu6es ardentes (hot, gas-charged avalanches of fluidized rock fragments), wereejected from the crater, so that much of the upper debrisflow was covered with more than seventy feet of finelypowdered ash and pumice.

The volcano remains active, with frequent small,harmonic tremors and occasional bursts of steam andash. Sizable eruptions, with their attendant smallpyroclastic and pumice flows, occuted on May 25, June12, July 22, August 7, October 17 and i,8, and December27 of last year. Future eruptions are expected, but mostgeologists believe that another large eruption is notlikely.

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BLAST ZONE

TREE BLOWDOWN

MUDFLOW

LANDSLIDE AND DEBBIS FLOW

PYROCLASTIC FLOW

FLOOD

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whether various species of forest treeswill show impo'rtant differences inmortality or productivity is not yetclear.

At higher elevations, snow pro-tected the plants beneath the canopyof forest trees from direct ash deposits,but impacts still accrued in this un-derstory vegetation. Many plant spe-cies already flattened by snow weretrapped by heavy ash. Erosion andrain may eventually remove sufficientash to free such plants, but the damagemay have been too severe or too muchof the growing season may have passedfor them to survive. Mosses and li-chens, which form low mats, are themost severely damaged. Other species,such as the erect-growing huckleber-ries (Vaccinium spp.), were able toemerge from the ash layer as the snowmelted. These plants grew well during1980, probably because there was lesscompetition from other plants and be-cause the high insect mortality re-duced grazing pressure. Many of theseemergents have sent roots into the nu-trient-rich ash and may thus benefitdirectly from improved nutrition.

Jim MacMahon of Utah State Uni-versity has shown that pocket gophersare major agents of ashJayer disrup-tion. These little burrowing rodentsimprove soil aeration and water in-filtration. As a consequence, mineralsfrom ash are more rapidly incorpo-rated into the soil, where they canbe used by plants. Silviculturists nor-mally view pocket gophers as unmiti-gated pests because they eat youngconifers, but for the next few years,gophers may prove valuable allies inthe reestablishment of tree seedlingsin clear-cuts and blowdown areas.

For most plant species, recovery inheavily ashed areas will be rapid.Young Douglas firs, silver firs, andnoble firs (Abies procera) may sufferheavy mortality, and species of li-chens, mosses, and other low-growingplants will be disproportionately rarefor many years, but overall forest pro-ductivity should soon return to pre-eruption levels. When nutrients fromthe ash, such as phosphorus and po-tassium, are added to the soil, theymay actually generate a pulse of en-hanced productivity. Understandingthe differential effects of Mount St.Helens'ash deposits on vegetation willimprove the ability of ecologists toread the history encoded in tree rings,pollen records, and soil profiles inother volcano-dominated ecosystems.

Less apt to survive than trees that

were primarily subjected to ash de-posits are the scorched conifers foundin a narrow but expanding band be-tween green timber and standing deadtrees. Many trees in this border zone,such as western hemlock (Tsuga het-erophylla), Douglas fir, and noble fir,survived the initial surge of heat andgas from the main eruption but wereweakened by it and also receivedheavy ash deposits. During the drysummer, many trees gradually suc-cumbed from internal heat or otherfactors. Fortunately, young saplingsbeneath many of these trees escapedvirtually unscathed by virtue of thesnowpack present during the eruption.Thus, the next conifer generation isalready well established and shouldexperience a burst of growth now thatthe saplings are released from com-petition with their parents.

Still closer to the volcano. wherestands of large trees did not survivethe first blast, stark contrasts appearbetween areas that had been clear-cut shortly before the eruption andareas that had been covered with for-est. In most parts of the blowdownarea, snow again offered some pro-tection to ground-layer vegetation, andterrain closest to the mountain re-ceived less ash than more distant areasdirectly in the path of fallout. In theclear-cut areas, regeneration of her-baceous vegetation began shortly afterthe eruption. Species that commonlygrow on recent clear-cuts, such asfireweed (Epilobium angustifolium),pearly everlasting (Anaphal i s mar gar-itacea), and bracken fern, have eco-logical characteristics distinct fromthose of forest understories. They growfast, produce many easily dispersedseeds, and are able to colonize newlydisturbed sites rapidly, tolerating highlight, high temperatures, and drought.

In contrast, areas in the blowdownregion that were covered by deep for-est at the time of the eruption lackedherbaceous vegetation as snows re-turned in the winter of 1980. The for-est understory normally consists ofherbs and shrub species adapted tocool, moist, dark conditions. Thesegrow slowly; produce few, poorly dis-persed seeds; and are intolerant ofhigh-light or high-temperature condi-tions. Any such understory plants thatsurvived the adverse impact of theblast and ash layers were thus con-fronted with an inimical environment.

Recovery in these blowdown areaswill require invasion by aggressive spO-cies from the surrounding clear-cuts.

As succession proceeds, conditions willgradually alter in favor of speciesadapted to the forest. A major pre-diction to be tested during the l98lgrowing season is that within the blow-down area, pioneer species from clear-cuts will make up the bulk of newgrowth in the once forested parts.However. since the flattened trees cre-ate microsites favorable to the survivaland regeneration of some understoryvegetation, the next forest generationwill be fostered by the slowly decom-posing remains of dead trees.

The potential juxtaposition of plantshaving markedly different ecologicalstrategies offers opportunities to testsome ecological theories. Prevailingopinion would predict, for example,that in open microsites, pioneer speciesshould outcompete the forest species,whereas in protected sites, the reverseshould happen. As conditions improve,overall dominance should rest with for-est species.

The region of tree blowdown andits surrounding ring of moribund treespresents the U.S. Forest Service withdifficult management options. Stand-ing dead and downed trees amelioratethe microclimate of the substrate, re-tard erosion. and foster natural suc-cession. Trees blown into stream chan-nels reduce erosion and siltation andpromote the recovery of streamsidevegetation and fauna. Furthermore,there is a widespread desire to pre-serve much of this region for inter-pretive, recreational, and scientificpurposes. The Forest Service, whichmanages most of the affected land,must reconcile these factors with thevalue of downed timber and the dan-ger of fire or of beetle infestationsin Douglas fir, starting in moribundvegetation and moving into healthy,economically valuable forests. Salvageremoval of downed timber is begin-ning, although not in areas designatedfor detailed study by the Forest Ser-vice Special Planning Team.

Flood plains are intrinsically unsta-ble habitats, and those in the areaaffected by the May 18 eruption willrecover more slowly than either theash or blowdown zones. The mudflows,which swept the lower thirty-two milesof the North Fork of the Toutle River,fifteen miles of the Muddy River, andmany smaller streams, removed mostof the vegetation in their path beforesettling into unstable masses. Erosionrates will be high, and successful seedinvasion will be limited for manyyears. Last July I observed cottonwood

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Oouglas C. Anderson

of the hypot-hesis that the recoveryrate on a site from which vegetationhas been totally obliterated dependson the proximity to a pool of colonists.According to this hypothesis, recoveryshould proceed much more rapidly onthe South Fork than on the NorthFork.

Experimental manipulat ions ofplots established on the debris flowsduring the next several years may alsohelp answer some general questionsabout succession. Is there a definitivesequence to the recovery pattern ordo chance and local seed availabilitydominate the process? Are the activi-ties of specific colonizing plant speciesrequired to facilitate the subsequentsuccess of other species? One way totest such hypotheses is by determiningwhether, after a number of years, plots

In many places, trees that withstoodthe blast were scorched by heat andnoxious gases and covered with ash.Where this occurred. the mountainshows a line between brown. deqdtrees and green, living ones.

(Populus trichocarpa) seedlings colo-nizing the lower North Fork of theToutle. Because they float through theair, cottonwood seeds were among thefew seeds available shortly after theMay eruption. Unfortunately, subse-quent erosion from minor summerrains washed these seedlings away.Bob Zasoski of the University ofWashington has estimated that morethan ten years will pass before thefirst trees are established on thesemudflows and more than a centurybefore a more or less normal forestcan develop.

Whi le mudflows devastated thelower river valleys, a huge debris flow-a turbulent, water-driven, hot massof rocks, boulders, and uprooted trees-ravaged the upper valley of the Tou-tle's North Fork. A few plants mi-raculously survived the vast jumble,and an occasional fireweed or brackenfern rhizome sprouted, but recoveryon this debris flow will depend pri-marily on seeds invading from lessdamaged areas.

Comparisons between the broad de-bris flow on the North Fork of theToutle River and the much narrowermudflow, close to intact vegetation,on the South Fork will provide a test

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from which the first cr:lgnists are pe-riodically removed differ from controlplots. Another question of interest iswhether succession tends to convergetoward a single community type orwhether initial site differences persistindefinitely. This question may be an-swered by comparing the initial degreeof vegetation heterogeneity with thatfound five or ten years later. Signifi-cantly reduced variety would implythat convergence is indeed occurring.

Several slower and less publicizedmudflows were driven by glaciersmelting on the east, south, and westslopes of Mount St. Helens. Last Sep-tember, I visited the upper portionof the six-mile-long Pine Creek mud-flow, which was propelled by the nownearly defunct Shoestring Glacier onthe southeast flank of the volcano.

Although the preeruption vegetationin this location is not known, the areastill reveals interesting aspects of vege-tation recovery. The heat and toxicfumes of the main eruption killed thesparse lodgepole pine (Pinus contorta)and subalpine fir (Abies lasiocarpa)scattered on the high ridges abovePine Creek. The subsequent mudflowdestroyed creek vegetation but itmerely buried the snow-covered dor-mant ground cover of the ridge. Ini-tially there was no vegetation on themudflow. which varied in thicknessfrom a few inches near the treelineto more than five feet at its upperend. The Cascade aster (Aster led-ophyllus) was the first plant to emergethrough this mud. Other herbs, in-cluding the broad lupine (Lupinus lat-ifulius) and Newberry's knotweed

(Polygonum newberryi), did notemerge until light rains created smallerosion channels along which theseplants were confined. Where mud wasmore than about a food deep, no vege-tation emerged in 1980.

Since mud seali the soil and canlimit oxygen exchange, buried vege-tation may be suppressed through theinhibition of root respiration. An al-ternative mechanism, however, mayoperate on mudflows and in areas ofheavy ash deposition. Both mud andash insulate the soil and create a lightbarrier.two characteristics of a snow-pack. Many plant species here andelsewhere may be fooled into "think-

ing" that winter continues. If this isso, as the 1980/81 winter snowpackmelts and further erosion cleanses themountain, surviving vegetation willemerge, having missed a growing sea-son but otherwise unscathed.

North of Pine Creek lies AbrahamPlains, a site that supported onlylimited vegetation prior to the May1980 eruption. After the initial erup-tion, pyroclastic and hot-ash flowsmelted snowfields on the mountain'snortheastern flank. The resultant mud-flows covered or removed all vege-tation on these plains. Revegetationin this area, unlike Pine Creek, willthus depend entirely on seed immi-gration.

The differences between recovervdue completely to immigration andthat abetted by residual vegetationwill be documented in permanentlymarked plots at Abraham Plains andPine Creek. Questions about succes-sion under stressful conditions will beaddressed. Do survivors and immi-grants belong to the same species? Or,as in the case of Abraham Plains, isthe habitat so severe that pioneers arethe only species capable of survival?Are differences in species compositiondue to dispersal failures or simply tothe absent species' inability to growin unaltered mudflow material? An-swers to such questions can be appliedto the future reclamation of derelict

Soon after the eruption, herbaceousvegetation began returning to recentclear-cuts within the blast zone.The pink flowers of fireweed, acolonizing species of disturbedareas, were a common sight.

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In what was once a large meadowcovered with hucklebeny bushes, alone spotted frog, right, rests next toa dying bush. To support thisamphibian, the meadow must stillhave some permanent water source.

Mammals, birds, and insects haveleft records of their wanderings inthe ash and mud, below. llthere thecrust is hard, the tracks of largeanimals provide traps for seeds andsuitable sites for germination.

lands in volcanic.regions-of the PacificNorthwest.

Further insight into recovery mech-anisms will' come from observationsof revegetation in sites on the periph-ery of the directed blast. The ridgesand glacial valleys in these areas es-caped the debris flow and pyroclasticactivity. On ridges above the SouthFork of the Toutle River, for example,the few lodgepole pines at timberlinewere killed by the scorching blast, butthe lush herbaceous vegetation thatnormally dominates these ridges, in-cluding the yellow penstemon (Pen-stemon confertus) and the broadleaflupine,. returned with no apparent illeffects. On the other hand, the glacialvalleys below the ridges, scorched bythe directed blast or scoured by mud-flows resulting from melting glaciers,

lost most of their vegetation. Nor-mally, these valleys support plants dif-ferent from those on the more exposedridges, but ridge vegetation is nowthe most likely source of seeds forthe newly exposed terrain. Mountainglaciers such as the ones that formedthese valleys ordinarily retreat slowlyenough for valley vegetation to keeppace. When Mount St. Helens erup-ted, however, the rapid melting of theglaciers not only exposed large areasfor the first time in more than a cen-tury but also washed away most veg-etation below the glacier. Thus, in theabsence of species specifically adaptedto the valleys, ridge species may ex-pand their habitat and create novelassemblages in the valleys.

Mount St. Helens is so young andits environment so harsh that even un-der normal conditions only the moregeneralized and stress-tolerant plantscan survive. All plants common to theupper slopes display adaptation to un-stable or chronically disturbed envi-ronments: deep taproots, buried grow-ing points, large storage reserves, andgood dispersal mechanisms. There-fore, although ridge-dwelling plantsmay under normal circumstances becompetitively inferior to valley dwell-ers, they may be physiologically ca-pable of surviving in the valleys. Iplan to monitor the development ofthe upper glacier valley vegetation tosee whether plant communities com-posed of ridge species do develop.Their existence in the valleys wouldbe strong, although indirect, evidencefor the importance of competition instressful environments.

Of all the regions on the moun-tain, the most severely affected wasthe blast zone immediately north ofthe crater, including Spirit Lake. Ev-ery type of volcanic behavior dis-played by the mountain has assailedthis terrain. All life was seeminglyobliterated. Trees were pulverized andsoil vaporized. Yet, even here, life isreturning. Forest recovery will be slow,but it will happen. Soil developmentwill require the establishment of mush-rooms, Iichens, and pioneering herbs.Seed and spore sources are scarce buta few pockets of vegetation remain.A protected ridge beyond AbrahamPlains, on the eastern edge of thisarea, for example, supports some silverfirs and a few areas of herbaceousvegetation.

Higher terrestrial life may be scarcein the blast zone but dead organicmatter is abundant, and such a re-

source is never unexploited for long.Here, where many humans died,where entire ecosystems ceased to ex-ist in a matter of seconds, Dave Hos-ford of Central Washington State Col-lege has found a mushroom, Autra-cobia melaloma, growing from theash, slowly decomposing organic mat-ter found there, and beginning a ter-restrial succession.

Most of the biological action in theblast zone, however, is taking placein lakes. Spirit Lake, once a pristineand clear body of water and now asappealing as a sewage lagoon, teemswith microscopic life. Bob Wissmarof the University of Washington, whois conducting a systematic survey ofthe affected lakes, has pointed outthat the water in Spirit Lake was to-tally removed by the force of the de-bris flow and replaced by a hot, muddyslurry of ash and debris. Thousandsof trees, blown off the mountain andwashed into the lake, have providedthe basis of a new aquatic food chainon the clogged water surface. As thewater cooled, blue-green algae andbacteria were the first active organ-isms, but decomposing anaerobic bac-teria and protozoans now dominate thebiota. The slowly dissolving organicmatter has reduced the oxygen contentof the lake and continues to releaseprodigious quantities of sulfur dioxide,the smell of which permeates the py-roclastic zone.

Many years will pass before SpiritLake and other profoundly alteredlakes return to a semblance of

'their

preeruptive state. Recovery will befaster in smaller, higher lakes, whichwere more thoroughly protected bythe snowpack. Higher lakes not hitby debris flows or mudflows were pri-marily affected by ash fallout and re-ceived only limited amounts of organicmatter.

Ephemeral lakes, laden with organicdebris and silt, pockmark the debrisflow that settled into the North Forkof the Toutle River. These lakes werequite warm throughout last summer,and decomposition in them was ram-pant. A witch's brew of phenolic acidsand tannins, smelling strongly of creo-sote and turpentine, is still drainingfrom them. Tracks of elk, deer, andcoyote are frequently encountered onthe debris flow where little food isevident, suggesting that the animalsmay well be in search of water. Un-fortunately, the quality of the waterin ephemeral and permanent lakes issuspect, On'one occasion, I found a

dead deer mouse, apparently poisonedby the tannin-blackened water in Cas-tle Lake, which formed when the Mayeruption dammed Castle Creek.

As I write, the winter rains cleansethe forest of ash. and snow falls onthe mountain slopes, restoring toMount St. Helens a pristine appear-ance. The volcano will undoubtedlyrumble for several years, however, andminor damage is likely to continue,particularly on the north slope. In suchareas, the biological recovery clockmay restart several times, providingfuture opportunities to observe severalstages of succession simultaneously.

Recovery on the mountain will goon for many years. At first, physicalchanges will predominate: wind willremove the dust, mud will erode, gla-ciers may recover somewhat. Manylakes and streams should recoverquickly, although the persistence ofheavy sediment loads will probablyretard the recovery of fish. In thehigher forests, snow-protected smalltrees will form the next generationand provide a forested look to muchof the blowdown area within fifteento twenty-five years. Above timber-line, as surviving vegetation emergesfrom beneath mudflows and ash. onlvsubtle differences from preeruptionconditions will be evident. Wherehigh-elevat ion vegetat ion was de-stroyed, however, revegetation will beslow and dependent on long-distancedispersal.

Foresters, ecologists, soil scientists,limnblogists, entomologists, and otherbiologists have coordinated their stud-ies of the biological aftermath of the1980 Mount St. Helens eruptions. Inour efforts to understand how ecosys-tems recover from such fundamentaldisturbances, we build on the workof pioneers. What we learn may, inturn, help us develop judicious waysto cope with future natural catastro-phes. No one wishes to experience fur-ther Cascade eruptions, but shouldthey happen, we will be better pre-pared to encourage rapid and effectiveecosystem recovery techniques. n

llith the afternoon sun obscuredbehind a ridge, fireweed blossomsscatter their luminous message oflife among the stumps of an earlierclear-cut operation four miles westof the peak of Mount St. Helens.

Ralph Perry

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