A. B. Adams, V. H. Oale',Botany Deparlment, Unversity of Washington,Seattle, Washington 98195 E. P. Smith'. Centerfor OuantitatrveScience Unversityof Washinglon,Seaftle Washington 98195 ano A. R. Kruckeberg,Bolany Departmenl, Universty of Washington,Seatte, Wash ngton 98195

PlantSurvival, Growth Form and RegenerationFollowing the 18 May1980 Eruption of MountSt. Helens,Washington

Abstract The conposition o{ piani connunilies changesafier cataclysrnssucb as volcanic eruptions.These comnunity changesnight be more accuralelyforecasl if lhe florislic compositionofcommuniries is known p.ior 10an e.uption becauserecovery ofplants dependsupon the mechanismsby which they nornally respond to disturbances.To identify sone o{ these mechanisns and their consequencesfor plant community recovery,we followed the recoveryof plani connunities after rhe l8 May 1980lateral blast of Mount St. Helens and eranined both speciesrhat survived and those lhat regenerated.Plants with sobterraneandor- nant buds (geophyte$and those lhat could regeneratefrom fregmentssurvived the eruption best.As a result, the proportion oi geophytespecies and relative plant cover of geophyres as significantly highe. than that of orher growth forn types.Initial recruihent onro the hummocky+urfaceddebris slide (i.e., nounded surface)was strongly biased toward geophyresand an- nuals, possiblr due to extreme enrironmental conditions on this new substrate.In contrast, olher habitats (blowdown,mud flow and scorched,dead forest)created by the e.uprion havehigher vegetationcover and are doninated by planls lhat surviyed ihe eruption. Becauseplants ha'e evol'ed in responseto frequent disturbancessuch as fires, snowslidesand floods, they are preadaptedto sinilar, bur less frequent, disturbancesthat are associatedwirh volcanic eruplions.

Introduction Influencesof climate,time, and substrate After large-scaleecosystem distuibance accurate have been formulated in a predictive model for assessmentsof plant regeneration are necessary long-term biomass accumulation on lava sub- for determining resource availability for ter- stratesby Eggler(19?l). Halpern and Harmon restrialand aquatic fauna, estimating the quan- (1983),based on initial observationsof revegeta- tity of sedimentto be expecteddownstream, and tion of the Lowerand UpperMuddy River mud assessingthe magnitudeof competitionthat com' flowat Mount5t. Helens,predicted successional mercialplantations may encounter.The effects patternsto be variablefollowing this volcanic of volcanicdisturbanccs on planlcommunilies disturbancebecause there is a varietyof surface andthe importanceof growthforms in plantre- substratesfor colonization,means of reproduc- source.Differential establishrnenthave been described (Smathers and tion and distancesto seed plant survivalwithin and betweendisturbance Mueller-Dombois1974, Man'ko 1974, Criggs past 1933, Franklin et al. 1985, Antos and Zobel typeshas not beenstatistically tested after debrisavalanches and associated lateral venting l985a,b),The pre-eruptiveinfluence of climate stratolayervolcanoes such as thosethat oc- andrecurrent disturbances such as fires, floods, of curred at Bandai-san, in IBBB(Sekiya and andsnowslides have been recently considered as Japan, Kikuchi lBB9),and at the Russianvolcanocs selectiveagents of adaptationsthat increasethe Bezymiannyin 1956and 1964(Tokarev l98l). probability of surviving eruptions (Adams and Criggs(1933) working four yearsafter the l9l2 Dale 1987,Antos and Zobell985a,b). A variety eruptionof Mount Katmai,Alaska, noted both ofplant responsesto burialhave been described the importanceand difficulty in differentiating by Antosand Zobel(1987) including the forma- betweenhold-over plants and new colonizers tion of adventitiousroots, upward growth of followingvolcanic eruptions. rhizomes,and movementof perennatingbuds. The eruptionsof Mount St. Helens,Wash- rCurrenr address: f,nironnental Sciences Dirilion, Oal ington(Lipman and Mullineauxl98l, Swanson Ridse National Laboratory, Oak Ridge, Tennelsee,3?831. et al. 1983,Weaver e, aL 1983,and Waitt el al. 'Cunent address:Statistics Dept., Virginia PolytechnicalInst. l9B3),provide opportunitiesto developmethods E Srat' t nirpr'irt.Bld.[.burg. Vireinra.2aOot for predictingthe mechanismsand magnitude of

160 Northwe"tScience, \ol.6l, \o,3, l9B7 r I

vegetationrecovery following cataclysmicerup- recordedthe numberof stems/speciesat the soil tions. Since quantifying differences in plant surface. growth forms rnouldallow us to substantiatpor refute past obseryations for vegetation following GroMh Form Classificationand Spectra other volcanic eruptions and provide a rneans for Plantswere classified by the locationof dormant assessingfuture successionaltrends, we decided meristematictissue relative to the ground sur, to use the Mount Helens blast zone to test St. face (Raunkiaer1934, Mueller-Domboisand growth for differential survival as a function of Ellenberg 1974).Crowth form spectrawere con- form. By looking in the time pe od immediate- structed for speciesclassified as annuals (A), Iy following the lateral blast, we were easily able plantswith budsbelow ground (G or geophytes), hold-over plants to separate from new colonizers. plants with buds at the ground surface (H or We believe that the rnethods results pre- and hemicryptophytes),plants with buds2.5 to 50 cm paper provide sented in this a simple way of us- above the surface (C or chamaephytes),tall pre-eruptive plant ing composition and associated shrubs (S), deciduoustrees (D) and evergreen plant poten- types of regeneration for forecasting trees(E). The percentof speciesfor pre-1980data tial plant recovery in the large- aftermath of a (256spp.) was constructed using the dataof St. scale natural disaster. John (1976).The growth form spectraof percent speciesfor the four disturbancehabitats were Methods determined using specieslists constructed on Samplingwithin Disturbance Habitats foraysthrough the habitatsand from established plots. The percent growth Thepost-eruptive habitats selected to examine cover of form types averagedfor the total areawas determined by differencesamong growth forms were: 1) blow- summingthe averagecover of eachgrowth form down;2) standingscorched (seared), dead forest; within a givenhabitat and then dividing this sum 3) mud flow; and 4) debris avalanche(Figure l). by the total number of habitats.The cumulative Ocularestimates of percentcover by species(ob- mean numberof individualsper plot was cal- tainedby dividing the plots into quartersand culated by dividing the total nurnberof in- summing to give a total estimatefor eachplot), dividuals of eachgrowth form by the number of the numberof speciesabove the ash,phenological plots and summingthe growthforms for each stages(seedling, emerging, immature plant, samplingperiod. flowering,setting seed or dead)represented by eachspecies, ash depth and distancefrom the Analyslsof Types of Plant Flegeneraton craterwere recorded for 25 m' circularplots from late June to Augustof 1980in blowdownand Threetypes of regenerationwere considered in scorched,dead forests, and mud flow habitats. our field work: 1) regenerationfrom newly Becauseplant cover was markedly lover on the depositedseeds (recruitment or establishmentof debrisslide relative to the other threehabitats nengpnets):2) reg"neraliUn from in si/asurviv- consideredin this research,we predictedthat ing plants; and, 3) regenerationfrom plant plant establishmentonto the debriswould be fragmentstransported by the energ] forces relatedfor the most part to survivalof seedlings. associatedwith the eruption (e.g.,the blast, This wouldallow a contrastof growthforms in avalancheand mud flows).The presenceof seeds a habitatrecolonized by seedswith habitatsin wasdocumented vith seedtraps (0.25 m') (Adams which a greaterproportion of the flora survived. and Adams1982, Adams and Dale 1987).Seed- Therefore,we consideredannual and seasonal lingswere distinguished from emergentresidual variability in growth forms on the debris slide plants by the presenceof cotyledonsand the by samplingover a threeyear period (15, 83 and absenceof "uLrtprranpanlissup frum prerious 103 250 m'?permanent circular plots during years'growth. Plants were unearthed to deter- Augustof 1980,l98l, and 1982,respectively) and mine if regenerationwas occurringfrom frag- for three time intervalsduring the summerof mentsor from ln sirz rootstockssprouting in 1982(June, July andAugust). In additionto the mineralsoil. To ascertainthe potentialof sub- informationcollected for the plotsin the other alpine lupine (Lupinus latifulius) to regenerate three habitats,for the debris slide plots we vegetatively,a singlelupine rootstockwas placed

Plant Survival,Grovth Form and Regeneration l6I Figure t. Map of study area relarive to rhe confluenceof tbe Cowlitz and Toutle Rivers and the Mount St. Helenscrater. The location of25 m'circular piots and transectsin 4 disturbancehabitats are shown.The bold letiers indicaie the dislur- bance type and the associatednunbers denole ihe nunber ofplols at eachlocarion. Disturbance types are blordown (B),standing scorched, dead forests (S), nud flowslM) and debris slide (D). The set ofplots designatedM9 represents 9 plols locared west of tbe map approximately I kn east of the confluenceof the Cowlitz and Tourle Rivers. The 250 n'zpernanent circular plots on ihe debris siide used in I980 ran soutb to north fron CasdeLake to Coldvater Lake and 3 plots were located on porlion of the debris slide that splashedacross Spirit Lake and was depositedjust north of Spirit kke. In l98I and 1982 the plots ran from 5 km east of the rerminus of the debris slide to Castle and Coldrater Lakes. Plots are spacedat 50 m intervals along line iransects in all habitats.

162 Adams,Dale, Smith and Kruckeberg in six claypots filled with debrissubstrate and flows and the debris slide) (Figure 2A). Since therootstocks were watered daily at the Univer- speciescompositions were identical for blowdown sity of Washingtongreenhouse. Methods used to anddead, scorched forests (100 spp.), these spec- determinesubstrate physical and chemicalprop- tra arepresented as a singlespectrum in Figure erties, and moisture stress troughs used in 2A. In the blowdownand scorched,dead forests, documentingregeneration from transpodedfrag- above-groundplant tissue was removed by the mentsare describedin Adamsand Dale(1987). lateralblast. Here most plantsregenerated in. sita. Over70 percentof thesespecies and 89 per- StatlsticalAnalyses cent of the relativecover consisted of plantsvith perennatingbuds belowthe ground.The mud To test the significance of distancerelative to flow (22 spp.)and debris slide (20 spp.)habitats ash depth in residual plant recovery,a multiple differed from the blowdownand scorched,dead regressionwas run utilizing numberof species forests by the occurrence of relatively fewer asthe dependentvariable versus ash depth and geophytes.The mud flow differedfrom the debris distanceas the independentvariables. To deter- slide spectra by having a higher proportion of mine the significanceof differencesin abundance speciesthat have buds projectingabove the of growth form types, a two-wayANOVA with mud's surface(shrubs )50 cm, deciduousand unequalfrequencies was performed on the log evergreentrees) and fewer specieswith buds transform + 0.0005)of percent cover with [Y below the surface. growthform and disturbancetype as factors.For the debrisslide data collected in permanent250 The barplots of eachseparate habitat repre- m2 circularplots during Augustof 1980,1981, sent the cumulative sum of the meansof each and 1982,a two-wayANOVA with unequal fre- growth form type (Figure 2B). Total mean per- quencieswas performed on the log transform of cent coverwas low in all four habitats( < 25 %), number of individualswith growthform and year but neverthelesshigher than we had expected. asfactors. Significant differences between growth Plantswith buds below the surfacerepresented form typeswere determined by computationof the highest percent cover/plot, followed by Scheffe'spair-wise contrast tests (Winer 1971). deciduousand then evergreentrees. A two-way ANOVA rnilizing percentcover with growthform Results anddisturbance type as factors, showed that the gror.rth form-disturbancetlpe interactionwas Similaritiesand Contrastsin GroMh Form significant(p < 0.001,F,s, 's = 8.02).Computa- Spectraof the Four Habltats tion of pair-wisecontrast tests indicated that the Disturbancetypes had different growthform rnaindifferences were associated with the relative spectra(Figure 2) and differenttypes of plant importance of conifers and deciduoustrees on regeneration.Annuals were poorly represented the mud flow and geophytesin other disturbance in the pre-eruptionflora and wereabsent from types.Tn 1980.pFrl'cnt corer for hemii"rlpto- all fourhabitats in thesummer subsequent to the phytesand treeswas lowl nevertheless,cover was eruptionof MountSt. Helens (Figure 2A). All six 16 timeshigher for plantswith budsat the sur- other growth form types were representedbv face and twice as high for treesin the scorched, residualor survivingspecies, The relativepro- deadforests than in the blowdown. portion of geophyteswas higher for the total area than existedin the pre-1980flora, whereashemi- [,4echansms of Regeneration cryptophytesand chamaephytesare notablyless. In 1980survival of seedlingswas found to be vir- No majorchanges in the relativeproportions of tually nonexistentin all four habitats(Adams and speciesof tall shrubs,deciduous or evergreen Adams 1982).In 1980regeneration in the blow- trees were noted when the spectrumfor the downand scorched,dead forests lvas almost en- pre-1980flora is comparedwith the cumulative tirely from in situ plant parts sprouting from percentof speciesfor the total. mineral soil. No regenerationfrom transported Growth form spectra of cumulative percent plant fragmentswas found in thesetwo habitats. of specieswere similar for blowdown and The numberof speciesregenerating seemed to scorched,dead forests, but thesetwo spectradif- be relatedto erosionin that the greatestnumber fered from those that occurred on lahars (mud of specieswere found on moderatelysteep slopes

Plant Sunival, Crowth Form and Regeneration 163 A tsf tao B H: ao gt 20 iico

60 r*: lJ ;P *; 4@ ;(n )= " 26 =l{ ;= :d- f,, -c] 0- o PRE- TOT^LSCORCH* XUO- OEERIS 1980 t^REABL0l{00rN FLoY SLI0E FLoR^k- SUMMER,1980 --j

tr r- !t C D t@o ::tQeo 0(* a@ z26A -tZf,= 60 qs >;i 40 ;: _^ 1E 2@ =t 1,, o 1,. r./ -o

MAY l99S NIRCH l9A2 tuoFL0fs NUOFLOTS figure 2. Crowth forn specira are reported for speciesclassified m annuals(A), planrs {iih buds belofi ground (C), planrs {ith buds at the ground surface(H), plantFvith buds 2.5 to 50 cn abov€ the surface(C), rall shrubs (S),deciduous rrees(D) and evergreentrees (f,). (Ai The percent of speciesfor pr€-1980daia (2s6 spp.)(Sr. John 19?6)and for 4 disturbancehabitats sampledfron June to July, I980. {B) The percent cover of gro{ih form types av€ragedfor the total area(sun o{averagecover ofeach habitat divid€d by the total nunber ofhabitats) and for rhe 4 disrurbance typ€s for 25m'lcircular plots sampled during July and Augnsi of 1980.(C and Dl Growth forn spectra for 250m' plots located on the debris slide. (C) Cunulative percent of speciesin debris avalanch€plois. (Dl Cunulative rnean number of individuals per plor calcujatedby diridins the totsl nunber of individuals of each growrh forn by rhe number of plots and sunning the growth fonns for each year. 0n 19 March 1982an explosiveeruplion gene.at€d a lahar that covereda large portion ofrh€ debris slid€ as far as 8lm fton rh€ crarer{q/aitt e, dt 1983).This second- ary disturbance is noied on Fis. 2C-D.

164 Adams, Dale, Srnith and Kruckeberg with gullies that penetratedthrough the ash to greenhouse(Adams and Adams 1982,Adarns er the surfaceof the pre-eruptivemineral soil. Multi- al. 1986).Lupinus Latiftlius becameestablished ple regression of data from blowdown and on the debrisslide and setseed in 1981.All six scorched,dead forestsshows number of species rootstocksections of this lupine placedin debris (N)25 m'?plot surviving and emergingabove rhe substratesprouted shoots and roots within two ash in July l9B0 to be related to depth of ash weeks. (D in cm), and not to distancefrom the moun- tain (N = 5.75 - 0.22D,p = 0.002,I = 0.40, Yearly and SeasonalTrends on the n = 50 plots); of distanceincreases I [addition Debrls Slide by 0.005 and the coefficient is not significantly different from 0 (p = 0.620)1.Regeneration from Only geophyteswere found in the debris slide iz sltu geophytesand hemicryptophyteswas rare plots in l9B0 and geophytesremained predomi- on both the mud flow and debrisslide. Regenera- nant in August samplesduring the three year tion from transported fragments occurred studyperiod. With the exceptionof smallshrubs, throughoutthe North Fork Toutle mud flow sites. all growthforms showed relatirc innreases in im- On the debris slide vegetativeregeneration was portanceto the total spectrasubsequent to 1980. mostly in rributary backfills and the outer Yearly changesin cumulativepercent of species margins of lateral terraces(Voight et al- l98l) in 250 m'?circular plots on the debrisslide were associatedwith rootwads,clumps of mineral soil pronounced(Figure 2C). In particular, the pro- and distal clumpsof forest fragmentsdeposited portion of annualsand deciduoustrees increased. at the westernterminus of the slide. Ahhoughtotal plant coverremained less than On the North Fork Toutle mud flow and percent slide through 1982, debris slide more than 20 speciesregenerated one on the debris of magnitude increase from hagmentsand from plants lransportedon there were three orders root wads,stumps and soil torn frorn the valley in the number of individuals/2S0m' plot from l9B0 to 1982(Figure 2D). The two-wayANOVA walls.Regeneration occurs from tubers lwestern with unequalfrequencies performed on number statflorlet (Trientalis latifu lia)l; corms [trillium- leavedwood-sorrel (Oxalis trilliifu lia)l; rhizomes of individualswith growth forrn and year as fac- torsvas significant(p<0.001, F,o,,o3 = 13.21). [beargrass(Xerophyllum tena.r)];and taproots The interactionof growthform with year wasin- [pearly everlasting (Caaphalium microcepha- lzrn)]. In 1980, on the debris slide, fireweed significant.Contrast tests indicate the main dif- (Epilobiumangustifolizm), Canadian thistle (Cir ferenceis due to the increaseof plantswith buds sium antense) and lady fern (Athyrium fi,lh- underground, and to a lesser degree to the femina) sprotted from axillary buds of changein annuals,and to an evensmaller incre- transportedrhizomes. In mud flow materialof ment of increasefrom deciduoustrecs. the North Fork Toutle valleylocated four km number of plantson the lvest of the debris slide terminus up to five In 1982the total and then fragmentsweie found sprouting within a 25 m2 debrisslide increased from Juneto July decreasedfrom July to August (Figure 2D). plot in l9B0 fMertens'sedge(Carex mertensii), dagger-leafrush (/uzczs ezsy'olius)and horSetails Deciduoustrees in 1982 showedan increase (Equisetum spp.) from rhizomes]. Broken throughoutthe samplingperiod but represented branchesof black cottonwood(Populus tricho' < l0 percentof the total number of individuals. corpo)and willows(So/ir spp.)developed leaves Annualsand geophytes show the largest increases and stemsfrom preformedprimordia embedded from June to July of 1982, whereas annuals in bark on stemsections on both the mud flow decreaseand geophytesremain unchanged from and debrisslide. Nine fragments[soft rush (/aa July to August. As expected,over 99 percent of cuselfusus), C. mertensiiar'd bentgrass (lglosris the increasein numbers of individuals on the d,iegoensis\fsprouted from mud flow substrate debrisslide was from seeddispersal and seed- spreadover an area of 13 m'?as part of a ling survival during l98l-82 aswas easily deter- moistureslress trough experimentconducted mined by the presenceof cotyledonsand lack of within the Universitv of Washinston research tissuefrom prcviousyears' growlh.

Plant Survival, Growth Form and Regeneration 165 Discussionand Conclusions lateralblast of Mount St. Helens.Plants that GeneralFeatures of the GroMh FormSpectra regeneratedin blowdownand scorched,dead foresthabitats also regenerate after fires (Miller The structureof florasurrounding Mount St. andMiller l9?6,Agee and Scott 1983, Hitchcock Helensboth beforeand after l9B0 is distin- and Cronquistl98l) and snowslides(Cushman guished from other vegetation at temperate 1981,Adams and Dale 198?).In the blowdown latitudes of the nofihern hemisphere as described andscorched dead forests, most surviving plants by Whittaker (1960), and differs from nearby vol- regeneratedftom in situ buds of rhizomes, canoessuch as Mount Rainier, Washington, by tubers, bulbs and corms. Antos and Zobel a high proportion of geophylesrelative to hemi- (1985a,b)found sinliar resultswhen investigating cryptophvtesand chamaephytes.After the crup- understoryspecies covered by tephrafrom Mount tion, survival and recruitment of growth form St. Helens.In addition,these researchers noted typesvaried significantly betweenhabitats con- that long-termsurvival was dependentupon sidered. The type and magnitude of vascular reestablishmentthrough the productionof adven- plant recovery in the first growing season follow- titiousroots within the tephra,as well as surviv- ing the eruption of Mount St. Heiens appeared ing the burial. Species with the ability to to depend upon the relationship between the regeneratefrom meristematictissue located nature of the disturbance which al area ex- severalcm belowthe surfacehave the greatest periences,aspect, time ofsnowmelt and ongoing survivalrate during fires (Flinn and Wein 1977, disturbances such as erosion. Mclean 1969).Also, in blowdownand seared forest habitats some tall shrubs Ie.g., Preadaptationto Firesand Snow thimbleberry (Rubusparoiflorus), salnonberry Periodicfires and climate(in particularheara (R. spectabilisl.and elderberry (sambucu's precipitation, much of it in the form of snow) may racemosa)fwhich had their aboveground parts explain, in part, the high proportion of geophytes destroyedby the blastresponded via adventitious in the floristin,^omposition of communitiessur- budsforming epicormicshoots as they do follow rounding volcanoesof the CascadeMountains. ing fires and snowslides.In this sensethese Similarly, the relatively frequeni eruptions of spei^iesaet as fa,.ultatir.geoph)les. Mount St. Helens (Mullineaux and Crandell l98l) Productionof new foliageby plantswith buds mar har'. a 5cie.liveeffccl regptation.truc- on at the surface,small shrubs, and coniferoustrees ture that resultsin proportion a higher of plants wasrestricted to areasprotected by snow,north with dormant primary meristematic tissue under- and northwestfacing slopes, or to the scorched, ground being found near Mount St. Helens.The deadforests in the caseof hemicryptophytesand chancesfor survival were found to be higher for chamaephytes.Plants of the PacificNorthwest plants buried by snow at the time of the erup- which possessbuds 2.5 to 50 cm aboveground tion (Means within the blast zone er ol 1982, leveloften have sclerophyllous evergreen leaves. Adams and Adarns l9B2), but the reverse r,as The total lossof buds and leavesexplains the found to be true in foreslsoutside the blast zone scarcityof smallshrubs in the devastatronzone where Antos (1982) and Zobel found reduced during the first growingseason following the cover at sites rvith tephra on top of snow for sprlngeruption. Both the proportionof chamae- shrubs, tree seedlings and erect evergreen herbs. phytespecies and their relativepercent cover had Antos and Zobel, in commenting on the scarcity decreasedfollowing the lB May eruption.Many ol X. tenax in habitats surrounding Mount St. chamaephytespecies [e.g., Oregon grape Helensrelative to its occurrence in similar habi (Berberisneruosa), salal (Gauhheria shallon) and tats in other parts of the Cascades,note that tim- twin flower(Linnaea 6oreolis)] are residualcom- ing of volcanic eruptions in relation to snow ponentsof burnedareas in the PacificNorthwest packs may greatly influence initial damage or sur- and regeneratevegetatively within a year after vival of vegetation. a fire (Miller and Miller 1976).These specres Montane forests and subalpine meadows of wouldbe expectedto be more abundantafter the Washington do have recurrent fires and eruption.Adventitious buds can form on roots snowslides which remove above-ground plant (especiallyinjured roots),but this is least likely biomassin a manner similar to that ofthe lB May to happenduring the spring (Hartmannand

166 Adams, Dale, Smith and Kruckeberg r

Kester 1975).Dispersal of small shrubsback into hasbroad implications for predictingthe poten- the devastationzone should be relatively rapid tial for vegetationrecovery in this habilattype. in the Pacific Northwest becallse birds and mam- Populus trichocarpa and SaLix spp. partially mals are major seedvectors fbr speciespossess- coveredby mud flowsactually produced seed in ing this growth form type (Best l98l). l9B0after the eruption,Other species, including conifers,seeded in 1981.The short.term survival Non-vascular plants that respond to fires were of treeson mud flowsprovided a seedsource, also the taxa that responded to the eruption of and snagsare more favorable habitat for ger- Mount St. Helens. For example, the most com' minationand growth.As such,their short-term mon mossfound during our ongoing studieshas survivalhas a significantimpact on future vegeta- been Funaria l4rgrometrica, a circumboreal tion trends.Our resultsare slightlydifferent than speciesoften found after forest fires and in camp- those of Halpern and Harmon (1983) who fire pits (Laryton l97l). Similarly, Discomycetes reportedresults for data collectedin l98l for the sporocarps (e.g., Peziza oioLacea ar.r).Pyronema MuddyRiver mud flowwhich is closerto Mount spp.)\lerpfound lhroughoul the devaslalion zone St.Helens than our mudflow plotson the North in 1980. These therrnophilic fungi are often Fork Toutle,and apparentlyhad much fewersur- found after fires and in pasteurizedsoil used in vivingtree snags in l98l thanwe found in 1980. greenhouses(Dennis l97B). Our work is similar to that of Halpern and Har- mon in thar we too found regeneration from Preadaptationto F oods fragmentsto be present,and we found microsites At Mount St. Helens,some disturbances were within habitatsto be diverseand to explainmuch similar to seasonalfloods causedby hearryrains ofthe diversityof the flora.Fragment regenera- and snowmelt.0n lowerportions of the Toutle tion appearsto be moreimpo ant on thc North and Muddy Rivers, and Pine and Swift Creeks Fork Toutle mud flow than on the the Muddy a slurry of mud, water and organic material River mud flow. washeddown from the mountainsweeping away muchof thevegetation. Marks on standingtrees Potentialfor FragmentRegeneration as a showthe waterlevels were as much as 15 m above Functionof Habtat normal stream levei as far as 33 km from the Fragmentswere dispersedby the energy crater of Mount St. Helens.The largestflows oc- associatedwith lahars. Vegetativc regeneration curred on the North Fork Toutle River where from transported fragments, such as that which conifersand broad leaf deciduous trees were left might occur following a flood, occurs in mud flow standingbut buried by metersof mud. Often and debris substrate. Regeneration from lrag- standingtrees had a ring ofbark removedby the ments has not been documented for volcanic force of the flow leaving the cambial layer eruptions. We found that mud flow and debris exPosed. slide materials possesspropenies that enhance Plant responsesafter mud flowsare similar their potential as rooting media (Hartmann and to methodsof regenerationthat thesesame spe- Kester 1975,Adams and Dale l9B7), such as: l) ciesutilize following floods. Observations frorn neutral pH (6.?t0.2, standard deviation);2)low the mud flowsof Kautz Creek,Mount Rainier, conductivity (lessthan two mmhosicm);3) suffi- Washington(Frehner 195?) and Mount Lassen, cient aeration due to a predominance of sand; California(Beardsley and Cannon 1930) indicate 4) moisture retention provided by silt and clay; that manytrees died up to threeyears after be- 5) a small, but significant quantity of nitrogen; ing partiallyburied probably due to insufficient and, 6) emplacement temperature of deposits hot oxygensupply to their roots or from cambial enough to kill root pathogens [e.g.,nematodes damage.On the Kautzmud flowburied trees set Heterodera) an,Jwater mo\r1s(Rhizophotinia anc) seed the following spring and fall, and tree Phfthium\\, bnt not too hot to destroy beneficial establishmentwas most abundantwhcre snags bacteria (maxirnum temperature for debris and providedprotection against ertreme tempera- mud flow rvas92'C) (Banks and Hoblitt l98l). turesand drought stress. Plant fragments were also dispersedby the The differencein the growth form spectrum force of the blast itself. The capacity for the of meanpercent cover for the mud flow habitat blast to dispersefragments is demonstratedby

PiantSurvival, Crowth Form and Regeneration 167 eye$itnessaccounts of the eruption.For exam- (Figure2C-D). Nevertheless, this disturbancedid ple, climbers at 2400 m on Mount Adams vary in the magnitudeof its impact on the debris reporledIhal plant fragments up to a melerin slide, depositingmore than I m of mud and Iength and conifercones landed around them pyroclasticmaterial in somespots to lightly man- shortly after 15:32U.T. on l8 May 1980 (a tling other areas(W aitt et aL.l9B3\.lf localized minimum of one fragment/I0m2)(Jack Chris- disturbancessuch as this havehigh ratesof oc- tiansen, pers. comm.). Fragments lyere found currenceson the debrisslide, annuals such as dispersedthroughout the blowdownand seared wood groundsel(Senecio syhtaticus) and annual forFsts.yet no fragmenlswere found rpgpnerating halrgrass (Deschampsia d,anthonioides) and here.In this case,fragment regeneration might geophytesadapted to chronic disturbancesmay hayebeen prevented by: l) high temperatures remain dominant here. With more moderate that destroymeristematic tissue and beneficial disturbancerates, deciduous trees may become symbionts;(blowdown and scorchemplacement established and survive by producing adven- temperaruresranged froIn 100to 350'C)(Banks titious roots, regeneratingfrom fragments,and andHoblitt 1981,Winner and Casadevall1983); dispersingcopious amounts of seeds. 2) coarserparticle sizesthat reducemoisture The distanceof seedsources from distur- retentivity; and, 3) an almost impermeable bancesites is critical to future vegetationtrends, cementJikelayer with low porosity createdwhen and is already a major factor in the Mount St. water combines with the fine-grained surface Helensarea, For example,redalder (Alnus rubra) tephra layer that coversmost of the potential (a major componentof flood plainsof western regenerationsites in the blowdownand seared Washington)did not survive in the blast zone. forests. Alnus rubra performs well when started from seedon both mud and debris substrate(Adams Vegetaton Trends on the Debris Slide er oL 1986),and this deciduoustree alreadyhas The debris slide underwenta significant change becomedominant on lower reachesof the l9B0 in growth forrn spectra from 1980 to 1982 and and l9B2 mud flow depositsin the North Fork showedseasonal variation in 1982.Although the Toutle floodplain where seedsources are near- proportion of annuals increasesin temperate by. This samespecies is rare on the debds slide zonesof the northern henisphere following dis- whereseeds are lesscommon. The rate at which turbances(Whittaker 1975),60 percent for the l. rubra establishesmay influencelong-term suc- July l9B2 debrisslide data is high. The reason cessionaltrends. For instance,if the disturbances for the abundanceof annuals is believedto be occurat evenlower frequencies, then a mixed due to the hot, dry conditionsthat existon the coniferousforest may have a chanceto become suface of the debris slide. Other habitats in the establishedprovided that l. rubra saplingsdo northwest(e.g., serpentine outcrops and arid not becomerapidly establishedand shadeout regionseast of the CascadeMountains) that sup- coniferseedlings. port high proportionsof annualsalso havehigh In our studiesat Mount St. Helenswe have temperature and low available water supplies. been able to establishthat plant growth form is Alpinelupine (Zapizuslepidus val. lobbifi,yellow importantnot only to initial recruitmentonto monkey-flower(Mimulus guttatus) and miner's newly depositedsubstrates of this stratolayer letnce (Montia sibirico) which are often peren- volcano,but in addition, is a significant factor nial, acted similar to many arid region species in the compositionand quantity of residual,sur- on rhe debris slide in that some individuals viving plant populations.Geophytes are not only floweredand setseed the first year and then died, the predominantsurvivors, but in addition,they thus beconing annual. Temporary strearnsand are importantin initial seedlingrecruitment from pools common on the debris slide provide the blowdownabove the Toutle River onto the ephemeralresources similar to deserthabitats. debrisslide. Annuals are able to exploit these temporary Groupsof speciespossess common adapta- resourcesand then spend the rnore slressful tions(c.g.. the position of dormantmprislematic periodsas dormantseeds. tissue)that influence sunival. Initial prognosis Overall,vegetation trends in our plotswere of the Mount St, Helensimpact areasunder- not set back by the 19 March l9B2 mud flow estimated the regenerative potential of the

168 Adams,Dale, Smith and Kruckeberg vegetation and overestimated the successof paper,We are especiallyappreciative ofJ. Frank- aerial seeding with non-native grasses(Brown lin (U.S.D.A. Forest Service),D. Jamison, K. 1981,Carlson et aL 1982).If mechanismsof sur- Russelland the WashingtonDepartment of Na' yival are understoodand the compositionof the tural Resourcesfor logisticalsupport and sugges- preexisting flora is knovn, then more accurate tions.We thankJ. Nishitani,R. Walker,D. Stuntz, predictions of speciesresponse and magnitude S, Kaluzny, and J. Creager for technical of vegetation recovery may be possible. assistance,the EarthwatchVolunteers, R. Holland and V, Dainesfor field assistanceand S. Cessel Acknowledgements for comments.This researchwas supported in part The authorsthank D. Chapman,B. Hallet,E. Leo- by the Centerfor FieldResearch (Boston, MA) and pold, S. Malone, B. Meeuse,R. Paine and M. was seeded with NSF emergencyfunding Slatkin for reading through initial drafts of this (DEB.B0-214,60).

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170 Adams,Dale, Smith and Kruckeberg