6 First-Year Recovery of Upland and Riparian Vegetation in the...

6First-Year Recovery of

Upland and Riparian Vegetationin the Devastated Area

around Mount St. HelensArthur McKee, Joseph E. Means,

William H. Moir, and _fen), F. Franklin

ABSTRACT

At the end of the first growing season following the May 18, 1980,eruption of Mount St. Helens, no vascular plants were found inregions subjected to pyroclastic flows, and plant cover on the debrisflow within the blowdown zone was estimated at 10-'%. The greatestplant cover within the devastated area was found on sites clearcutbefore the eruption; for these sites, the mean was 3.8% and the maxi-mum sampled value was 17.2%. Areas of blown-down forests without asnowpack at the time of eruption had a mean plant cover of only 0.2%(maximum value of 0.66%). The presence of a snowpack during theeruption greatly ameliorated the effects of the blast and the associateddeposits of ash on understory plants. Riparian areas had the greatestspecies richness, probably because of more favorable microsites foundalong streams and created by their action. Favorable microsites werealso critical for plant survival and regrowth in upland habitats. Virtu-ally all the live plants were perennials that had sprouted from thepreeruption soil and had penetrated the ash or had been protected by asnowpack.

INTRODUCTION

The violent eruption of Mount St. Helens on May 18, 1980, de-vastated 61,000 ha of forested terrain north of the volcano (USDAForest Service 1981a). The features of that and subsequent eruptionsare described in detail by Lipman and Mullineaux (1981). The tre-mendous landslide, the powerful lateral blast, subsequent mudflows,

6c

168

RECOVERY OF VEGETATION 169

ashfalls, and pyroclastic flows all combined to create a variety of newhabitats for revegetation (Fig. 6.1). Areal extents of these major habi-tats are estimated in Table 6.1.

The landslide resulting from the collapse of the north flank ofMount St. Helens on May 18 formed a debris flow that moved 24 kmdown the North Fork of the Toutle River, Primarily consisting ofrubble from the mountain, it also included some topsoil and variousplant parts such as rhizomes, roots, and stems that could possiblysprout under appropriate conditions. To the northwest, north, andnortheast of the peak, forests as far away as 28 km were flattened by thepowerful lateral blast, forming a blowdown zone. A scorch zone ofstanding dead trees that had been killed by heated gases formed a bandof varying width around the blowdown zone. Within the blowdown

FIG. 6.1 Mount St. Helens and vicinity. Note location of debns and pyro-c.lastic flows, tree blowdown, scorch zone, and mudflows.

170 ARTHUR MCKEE ET AL.

zone, nearly all above-ground plant parts not buried in snow werekilled on May 18. In the scorch zone, although mortality was extreme,some above-ground plant parts survived the eruption. Rapidly meltingsnow and ice and other processes created mudflows that filled streamchannels and buried existing soils at depths of several meters. As in thedebris flow, plant parts that could potentially sprout were incorporatedinto mudflows.

Ejects from the blast and subsequent ashfalls formed deposits oftephra ranging from 10 to 60 cm deep or more. Pyroclastic flowsassociated with the explosive eruptions of ash raced down the northflank of the volcano, fanning out over the debris flow and areas sub-jected to earlier pyroclastic flows. The pyroclastic flows were totallydevoid of plant parts that could reproduce vegetatively and thusformed a habitat for primary succession.

Prior to the May 18 eruption, the upland and riparian vegetationconsisted of a productive conifer forest dominated by Pseudotsugantenziesii, Abies amabilis, Abies procera, Tsuga heterophylla, and Thuja pli-cata, The forests ranged in age from young stands in areas recentlyclearcut to old-growth forests over 500 yr in age (USDA Forest Service1981b). The dominant trees in mature stands were >1 m in diameter atbreast height and >50 m tall. Basal areas of such stands ranged from 60to 110 m2/ha.

Logging over the last three decades had created an array of standsin various stages of secondary succession. After the eruption, thesestands could be expected to have very different capacities for vegeta-tive recovery than those of mature forests. Riparian vegetation alsoshould respond differently from upland vegetation, which is subjectedto less favorable moisture conditions.

Aerial reconnaissance prior to the study revealed that con-spicuous differences existed in the first-year recovery of vegetation inthe major habitats within the devastated area, which included thedebris flow, mudflows, pyroclastic flows, clearcuts, blowdown, andstanding dead forests. Moreover, the presence of a snowpack at thetime of the May 18 eruption had apparently enabled some low shrubsand seedlings to survive. Riparian vegetation also appeared to berecovering more rapidly than the upland vegetation.

In light of these preliminary observations, the primary objectivesof this study were as follows: (1) to document first-year patterns ofrevegetation in the major habitats created within the devastated area;(2) to compare vegetative recovery in forested areas clearcut prior tothe eruption, in blown-down forests, and in standing dead forests; (3)to investigate the effect of snowpack in the blown-down forests on


plant recovery; (4) to compare recovery of riparian vegetation on sitesin the devastated area with that on sites receiving only ashfall; and (5) toestablish a network of permanent plots for the study of vegetativerecovery in the future.

METHODS

Several sampling methods were required to deal effectively with therange of spatial variation in the major habitats. Because of their barrennature, debris and pyroclastic flows were sampled by establishing tran-sect lines and noting the presence of a plant species within 5 m of thetransect. Areas subjected to the pyroclastic flows were sampled at threesites ranging from 1020 to 1200 m in elevation. At each site, threetransects 250-300 m in length were sampled. A 2750-m transect wasestablished at 800 m elevation on the debris flow in the valley of theNorth Fork of the Toutle River.

Clearcuts and blown-down and scorched forests were sampled bytransects consisting of five 250-m 2 circular plots spaced 25 m apart.These transects were normally installed as adjacent pairs (occasionallytriplets) to allow comparisons among clearcuts and blown-down andscorched stands. The percentage of cover for each species was esti-mated in each 250-m' circular plot. The nature of the tephra wasdescribed and its depth measured at least once in every plot, In everyplot the coverage of woody debris was measured by an intercept linealong a diameter placed at right angles to the direction of blowdown. Atotal of 35 transects were established in 1980: 13 in clearcuts, 13 inblown-down forests without a snowpack during the eruption, 6 inblown-down forests with a snowpack during the eruption, and 3 inscorched forests. Sites that had a snowpack during the eruption werereadily recognizable because the tephra had slumped and crackeddistinctively as the snow had melted from beneath.

The riparian vegetation along streams was sampled in 10-m-widebelt transects oriented perpendicularly to the main streamflow. Thetransects spanned the active, border, and outer riparian zones as de-fined by Campbell and Franklin (1979). The active zone included thatportion of the riparian habitat subject to normal annual strearnflow.The border zone included any area from which litter could reach thestream after some delay. It included, but was not restricted to, areasthat flood during unusually high flows. The outer zone included thearea within the influence of the higher water table near a stream, asevidenced by topography, vegetation, or both.


Five transects were established for riparian vegetation in 1980:three in the blast zone and two in nearby areas with just ashfall. Alongthe ashfall transects, plant cover was sampled in 0.2 x 0.5 m micro-plots spaced 1 m apart on 10-m-long subtransects perpendicular to themain transect and spaced 5 m apart. Species cover was assigned to oneof six classes at each microplot, and the midpoint of the range of thecover class was used during the data reduction (Daubenmire 1959).

Vegetation was so sparse in the devastated area that cover for aspecies was estimated on the 5 x 5 m subplots formed by the maintransect and subtransects. Because microsites apparently played a keyrole in the recovery patterns of riparian vegetation in the devastatedarea, the percentage of each 5 x 5 m subplot occupied by differentmicrosites was estimated. These microsites were later grouped into sixtypes: (1) steep banks and streambanks, (2) areas beneath elevated logs,(3) rootwads and tops of logs, (4) sand or gravel bars and overflowchannels, (5) active channels, and (6) intact tephra. Tephra depositswere always reduced in the first three types of microsites because of thesite steepness or the shelter provided by a fallen log. Tephra was often<5 cm deep on these microsites. The intact tephra microsites hadundergone little or no disturbance or removal of the tephra sincedeposition.

The riparian vegetation around Meta Lake, located 13 km north-east of the volcano at 1080 m elevation, was sampled by five transectlines. Three of these were in the emergent wetland zone, and two werein the surrounding scrub shrub zone (Cowardin et al. 1979). Eachtransect consisted of 30 0.2 x 0.5 m microplots spaced 1 m apart. Plantspecies and seedbed substrates were assigned to one of six cover classes,and the midpoints of the ranges of the cover classes were used duringdata reduction (Daubenmire 1959).

Reconnaissance and sampling were conducted over a 2-weekperiod in mid-September 1980. Helicopters were required to travelinto the devastated area, and safety regulations limited the distancethat sampling crews could travel from the landing sites. Because ofdifficult access, most sampling was confined to the northeastern por-tion of the devastated area (Fig. 6.1).

RESULTS

UPLAND VEGETATION

No vascular plants were found along the transects in areas subjected topyroclastic flows, nor were any revealed on these barren surfaces byextended reconnaissance. The debris flows were almost as devoid of


vascular plants as the pyroclastic flows. In September 1980, total plantcover on the 2750-m transect was estimated at 10-°%; it consisted ofonly two small plants sprouted from rootstocks: a fireweed, Epilohumangustifolium, and a lady fern, Athyrium filix-femina.

Total plant cover was very low at all sites in clearcuts, blown-downforests without snowpack on May 18, and scorched forests (Table 6.2).The maximum value of 17.2%, obtained in a clearcut stand, was severaltimes the maximum sampled in blown-down forests without snowpackor scorched forests. None of the sites sampled in the latter two habitatshad even 1% total live plant cover. When two-way comparisons of plantcover and number of taxa per transect were made with a paired t-test(Snedecor and Cochran 1967), clearcuts had significantly more plantcover than did blown-down forests without snow (p = 0.05). They alsopossessed 10 times more plant cover than did the scorched forests,although the difference was not significant (probably because of thelimited sampling of scorched forests).

Species richness in the three upland habitats was similar to coverat the end of the first growing season (Table 6.2); the number of taxaper transect was low in all habitats sampled. The mean number of taxafor clearcuts was significantly larger than that for blown-down forestswithout snowpack (p = 0.10) or scorched forests (p = 0.01), beingabout twice as large.

Almost all the plant species encountered on the transects hadsprouted from plant parts located beneath the preeruption soil sur-face, but there were two types of exceptions. The most common wasgrass seedlings established from a seeding program by the USDA SoilConservation Service in the late summer of 1980 (Stroh and Oyler1981). The other exception was found in scorched forests near themargin of the devastated area, where the hot blast cloud had appar-ently cooled sufficiently so that occasional stems of deciduous shrubssurvived and sprouted epicormically.

The presence of a snowpack at the time of the May 18 eruptionameliorated the effects of the blast on the understory vegetation (Table6.3). In stands located between 1100 and 1340 m elevation, blown-down forests with snowpack had significantly greater plant cover thanthose without snowpack (p = 0.05). Although there was no significantdifference in species richness between the two habitats, the maximumspecies richness (n = 21) among all the upland transects occurred in ablown-down forest with snowpack. Unfortunately, no clearcuts orscorched forests with snowpacks could be sampled for comparison.

The frequency of the most common taxa found on the transectsin the upland habitats is shown in Table 6.4. The variation in plantspecies in the various habitats partially explains the differences


observed in first-year vegetative recovery. The most common speciesin the clearcut areas were early successional plants that sprout vigor-ously and are well adapted to full sunlight (e.g., fireweed, Epilobiumangustifolium; pearly everlasting, Anapha/is margaratacea; and thimble-berry, Rubus panfloru.^). In contrast, common shrubs and saplingsfound at higher elevations (such as huckleberries, Vaccinium spp.; silverfir, Abies amabilis; and mountain hemlock, Tsuga mertensiana) domi-nated the blown-down forests protected by snowpack. In addition tothe thermal insulation provided by the snowpack, the mechanicalprocesses of cracking and slumping of the tephra as the snow meltedfrom beneath provided thin spots and avenues whereby plants couldmore easily reach the surface. The sites with snowpacks also tended tobe on the north-facing slopes in the lee of the blast.

The most common species encountered on transects in blown-down forests without snowpack were low shrubs. These had sproutedfrom plant parts located beneath the old soil surface. Most of theindividuals were depauperate, in marked contrast to the vigorous earlysuccessional plants found in clearcuts. While the distribution of plantsin microsites was not quantified, the plants in blown-down standswithout snowpack were most commonly found on steeply angled rootwads or under fallen tree boles at sites where the tephra had notaccumulated as deeply as on open, level ground.

The relationship between plant cover and tephra depth in clear-cut areas is complex because of the interactions of many factors, includ-ing the intensity of blast, temperature of deposits, composition of thetephra, and time since clearcutting occurred. The correlation of totalplant cover with depth of tephra is poor (Fig. 6.2). The highest plantcover occurred at a site covered with slightly more than 20 cm oftephra. Some of , the lowest values, however, were found at sites withthis same depth of tephra. The site with the highest cover was deeplyrilled, and plant recovery was greater in those microsites with thinnertephra. Erosion within the devastated area will clearly play a major rolein vegetative recovery.

Earlier reconnaissance flights suggested a gradient of increasingplant cover as the distance from the volcano increased. This was notunexpected, because the intensity of the blast diminished away fromthe crater. The tephra depth also was reduced as the distance from thevolcano increased. Except for one site, total plant cover in clearcutsincreased with distance from the volcano (Fig. 6.3). At distances of<15 km from the volcano (where tephra depths were >20 cm), thecover declined to almost zero. Without exposure of the soil by erosion,plants had a difficult time penetrating tephra depths of >20 cm(Fig. 6.2).

RECOVERY OF VEGETATION

175

TEPHRA DEPTH (cm )

FIG. 6.2 Plant cover in September 1980 in areas clearcut prior to the May18 eruption versus depth of tephra. Tephra depth determined by a minimumof five soil pits per site.

If tephra depth and distance from the volcano are held constant,the major upland habitats can be ordered from the greatest total plantcover to the least as follows: clearcut, blown-down forest with snow-pack, scorched forest, and blown-down forest without snowpack. Theranking for species richness from greatest to least is: blown-downforest with snowpack, clearcut, scorched forest, and blown-down forestwithout snowpack. The eruption drastically reduced plant cover andspecies richness within the devastated area. Indeed, the values on thedisturbed sites often approached or equaled zero. Undisturbedforested sites in the region would normally have plant covers of 100%or more, and species richness on plots of similar size would be five toten times greater (Dyrness 1973, Dyrness et al. 1974).

20 1 I I I I F I

•

15

•10 •

5 • _


RIPARIAN VEGETATIONDespite the apparent greenness of riparian areas from the air, sam-pling indicated that vegetative recovery was occurring there at aboutthe same rate as on upland sites or perhaps even more slowly. Recoveryduring the first growing season depended on microsite conditions, and(as with upland sites) all riparian individuals in the devastated arearesulted from vegetative reproduction from below-ground plant partsthat survived the blast.

Total plant cover in riparian areas of the devastated area was verylow, especially when compared to riparian transects in the nearbyashfall area (Table 6.5). The plant cover in the border and outerriparian zones of the ash fall area was within the range expected in thePacific Northwest in undisturbed areas (Henderson 1978, Campbelland Franklin 1979). Values for total plant cover were low in the activezone for both the devastated and the ashfall regions, probably becauseof scouring by rapidly flowing streams heavily loaded with ash andpumice.

•

_

•

10 15 20

DISTANCE FROM CENTER OF VOLCANO (Km))

FIG. 6.3 Plant cover in September 1980 in areas clearcut prior to the May18 eruption versus distance from the center of the volcano.


Little difference in species composition existed between the ripar-ian habitats in the ashfall and in the devastated areas (Table 6.6). Thespecies found in riparian areas were typical of riparian sites west of theCascade range (Henderson 1978, Campbell and Franklin 1979).

After adjusting for varying plot sizes, species richness was greaterin the ashfall area than in the devastated area (Table 6.5). This patternwas consistent with earlier preliminary observations. Some similarityoccurred in the number of species encountered in the border zones ofthe two habitats, possibly because the overlying tephra was removed byhigh streamflows with limited scouring during storms. Such actionwould permit sprouting through the thinner layer of tephra and con-sequent growth without major scouring damage.

Previous reconnaissance suggested that microsite differenceswere important in riparian habitats in the devastated area. Accord-ingly, the riparian transects were stratified by microsite and covervalues normalized for microsite area (Table 6.7). Microsites with rela-tively thin tephra deposits, such as streambanks and steeply tiltedroot wads, tended to have the highest cover values within a transect.The lowest values were found on intact or very slightly reworkedtephra. The microsites with the most plant cover comprised only about5% of the total area sampled by transects. These islands of green in anotherwise gray world will undoubtedly be an important source ofpropagules for recolonization of the riparian habitats in the devastatedarea.

Total plant cover and number of taxa per transect around MetaLake are shown in Table 6.8. The highest cover in this shoreline areawas found in the emergent zone, but slightly more taxa occurred in thescrub shrub zone, which is located at a slightly more elevated positionaround the lake. Both cover and species richness, however, were low inall the zones. The dominant species found in the three zones aroundMeta Lake are shown in Table 6.9. The species composition suggeststhe presence of a snowpack on the shore of the lake at the time of theblast. Only on blowdown sites with a snowpack were Vaccinium spp.,Menzzesia ferruginea, and especially Abies antabilis found with coveragesas high as around Meta Lake.

The distribution of plant species around Meta Lake also sug-gested a possible interaction between snowpack and tephra deposition(Table 6.10). The north shore (which faces south) had a relativelygentle slope; consequently, little tephra washed into the lake. Also, thisshore had either no snowpack or just a thin one at the time of the blast.The emergent zone species, Carex aquatiiis, was protected from theblast by the water and was doing well. Vegetation in the scrub shrub


zone not protected by a snowpack was impoverished, unlike that on thesouth shore. The north-facing south shore had a snowpack thatoffered some protection to plants of the scrub shrub zone. The southshore was steep, however, and an alluvial fan of tephra covered muchof the emergent zone. The low cover values in the emergent zone werepossibly a result of relocated tephra burying the emergent plants.

More streamside than lakeside sites were examined by both sam-pling and preliminary observation. It should be emphasized that thesmall number and restricted distribution of sampled sites precludedstatistical testing of hypotheses concerning riparian recovery. Thepatterns observed, however, appeared to be consistent with more ex-tensive observations at other sites.

DISCUSSION

While the overall impression of the devastated area in mid-September,1980, was that its designated name was appropriate, vegetative re-covery had begun on all of the major habitats except those areassubjected to pyroclastic flows. The recovery during the first growingseason had several interesting characteristics:

Virtually all species of vascular plants present were perennialsthat had sprouted from below the sod surface and had penetratedthe ash or were protected by snowpack.Within the devastated zone, the presence of a snowpack at thetime of the eruption was an important factor in moderating theeffects of the blast.Total plant cover was greatest in clearcut sites because of theability of early successional plant species to reproducevegetatively.Total plant cover was minimal in blown-down forests withoutsnowpack because of the apparent inability of forest understoryspecies to resprout vigorously.Species diversity was greatest in riparian habitats; this was afunction of the diversity of microsites created by the action of thestreams.Within riparian habitats, the active zone was extremely low inboth plant cover and species richness.

7. The emergent zone had greater plant cover than the scrub shrubzones around lakes, but the latter had greater species richness.


Microsite conditions were key factors in survival and reestab-lishment in both riparian and upland habitats.Strong environmental and vegetational gradients existed withinthe devastated area, with both elevation and distance from themountain.

The future pattern of revegetation will be a function of severalfactors, including the influx of plant propagules, rates of vegetativereproduction, erosional processes on upland and riparian sites, log-ging and reforestation activities, and of course, future eruptions of themountain. The soil that lies buried beneath the tephra also will play akey role in revegetation. This soil once supported productive forestsand remains intact over most of the area. Virtually all of the vegetationappearing during the first growing season sprouted from, or wasrooted in, this buried soil. These plants will serve as important sourcesof propagules.

The tephra is a poor medium for plant establishment andgrowth. Samples of the tephra taken within 30 km of the volcano werevery low in nitrogen (0.018%) and phosphorus (4.81 ppm) and had apoor cation exchange capacity (2.86 meq/100 g) (unpublished data,G. Klock, USDA Forest Service, Wenatchee, Washington). The trialseedings by the USDA Soil Conservation Service were most successfulwhen grass and legume species were able to reach the buried soil (Strohand Oyler 1981). Those plants that were rooted only in the tephrashowed severe nutrient deficiencies.

The recovery of this devastated area will most likely be rapidrelative to many other volcanic eruptions because the soil buried be-neath the tephra is within the rooting distance of many plants. Lavaflows and thick tephra deposits characteristic of other eruptions slowrevegetation and couple it to soil formation processes. Smathers andMueller-Dombois (1974) provide a good review of posteruption re-vegetation.

Removal of the overlying tephra by erosion will hasten uplandrevegetation by allowing sprouts from buried vegetation to reach thesurface more easily and by reducing the distance a developing rootmust grow before entering the nutritionally rich soil. Rapid revege-tation after exposure of the buried soil has been observed at KatmaiNational Monument (Griggs 1919) and Paricutin Volcano (Eggler1948).

Recovery of the riparian vegetation will possibly be adverselyaffected by the erosional processes that enhance hillslope revegetation.The erosion of tephra into the riparian zone with subsequent re-


working by fluvial processes could dramatically slow the recovery of theriparian vegetation. Regrowth may be buried by aggrading streams orseverely scoured by the higher flows. Under heavy loads of sediment,stream channels will be less stable and the rate of new channel for-mation will be increased, with consequent undercutting and removal ofstreambank vegetation. For the next few years, the woody debris in andnear stream channels will probably have a greater influence on channelmorphology than will the recovering vegetation. Removal of the coarsewoody debris by salvage logging will further destabilize the system andmay have a profound effect on geomorphic processes and recoveryrates of the riparian vegetation.

Further study of the devastated area should result in a betterunderstanding of ecosystem recovery, particularly as it pertains to thelandscape of the Cascade range. From Mount Rainier to Mount Lassen,the Cascade range has been formed by relatively recent volcanism(McKee 1972, Crandell et al. 1975, Heusser and Heusser 1980,Hoblitt et al. 1980). Thus the 1980 eruption of Mount St. Helens is notunique. Past volcanic activity has probably determined the currentpattern of vegetation in the Cascades in such diverse ways as depositingtephra of different chemistries and depths and reducing or eliminat-ing plant species in heavily impacted areas. Detailed study of therevegetation in the devastated area around Mount St. Helens shouldcontribute to an understanding of the relative importance of variousenvironmental factors on the region's forest and riparian ecosystems.

ACKNOWLEDGMENTS

Several people contributed to this paper. Miles Hemstrom col-laborated in the initial sampling design for upland vegetation and led afield crew. Diane Mitchell, Sarah Greene, and Robert Frenkel assistedin riparian sampling. Fred Bierlmaier, Judy Alaback, Peter Frenzen,Glenn Hawk, and Robin Graham were among the many people of thefield crew who worked for long periods and contributed many ideas.This study was supported by the Pacific Northwest Forest and RangeExperiment Station of the USDA Forest Service, by Oregon StateUniversity, and by National Science Foundation Grant DEB 8024471to Oregon State University. This is Paper 1648 of the Forest ResearchLaboratory, Oregon State University.


LITERATURE CITED

CAMPBELL, A. G., and J. F. FRANKLIN. 1979. Riparian vegetation in Oregon's WesternCascade Mountains: Composition, biomass, and autumn phenology. ConiferousForest Biome Bull. 14, 90 pp. U.S./International Biological Program, Univ. of Wash-ington, Seattle.

COWARDIN, L. M., V. CARTER, F. C. GOUT, and E. T. LARoE. 1979. Classification ofwetlands and deepwater habitats of the United States. FWS/OBS-79/31, 103 pp.Office of Biological Services, Fish and Wildlife Service, U.S. Department of theInterior, Washington, D.C.

CRANDELL, D. R., D. R. MULLINEAUX, and M. RUBIN. 1975. Mt. St. Helens volcano:Recent and future behavior. Science 187:438-441.

DAuBENMIRE, R. F. 1959. Canopy coverage method of vegetation analysis. Northwest Sci.33(1):43-64.

DECKER, R., and B. DECKER. 1981. The eruptions of Mount St. Helens. Sa. Am. 244(3):68-80,

DYRNESS, C. T. 1973. Early stages of plant succession following logging and burning inthe western Cascades of Oregon. Ecology 54(1):57-69.

DYRNESS, C. T., J. F. FRANKLIN, and W. H. Mont. 1974. A preliminary classification offorest communities in the central portion of the western Cascades in Oregon.Coniferous Forest Biome Bull. 9, 123 pp. Univ. of Washington, College of ForestResources, Seattle.

EGGLER, W. A. 1948. Plant communities in the vicinity of the volcano El Paricutin,Mexico, after two and a half years of eruption. Ecology 29(4):415-438.

GRIGGS, R. F. 1919. The main character of the eruption as indicated by its effects onnearby vegetation. Ohio J. Sci, 19(3):173-209.

HENDERSON, J. A. 1978. Plant succession on the Alnus rubral Rubus spectabilis habitat typein western Oregon. Northwest Sci. 52(3):156-167.

HEUSSER, C. J., and L. E. HEUSSER. 1980. Sequence of pumiceous tephra layers and thelate Quaternary environmental record near Mount St. Helens. Science 210:1007-1009.

HtifiErrr, R. P., D. R. CRANDELL, and D. R. MULUNEAUX. 1980. Mount St. Helenseruptive behavior during the past 1,500 years. Geology 8:555-559.

LIPMAN, P. W., and D. R. MULLINEAUX. 1981. The nineteen eighty eruptions of MountSt. Helens, Washington. U.S Geol. Surv. Prof Paper 1250, 844 pp. U.S. Govern-ment Printing Office, Washington, D.C.

McKEE, B. 1972. Cascadia. McGraw-Hill, New York. 394 pp.ROSENFELD, C. L. 1980. Observations on the Mount St. Helens eruption. Am. Sarni.

68(5):494-509.SMATHERS, G. A., and D. MUELLER-DOMBOIS. 1974. Invasion and recovery of vegetation

after a volcanic eruption in Hawaii. U.S. Nat, Park Se v. Scant. Monogr. Ser. (No. 5),129 pp. Washington, D.C.

SNEDECOR, G. W., and W. G, COCHRAN. 1967. Statutical Methods. (6th ed.). Iowa StateUniv. Press, Ames, Iowa. 593 pp.

STROH, J. R., and J. A. OYLER. 1981. Assessment of Grass-Legume Seedings in the Mt.St. Helens Blast Area and the Lower Tousle River Mud Flow, May 1981. USDA SoilConservation Service, Spokane, Washington.

USDA FOREST SERVICE. 1981a. Draft Environmental Impact Statement-Mount St. HelensLand Management Plan. Gifford Pinchot National Forest, Vancouver, Washington.162 pp. plus 24 maps. 1981b. Preliminary Plant Association and Management Guide for the Pacific Silver Fir

Zone of the Gifford Pinchot National Forest. Pacific Northwest Region, Portland,Oregon, 123 pp.

U.S. GEOLOGICAL SURVEY. 1981. Mt. St. Helens and vicinity (map). Available fromGifford Pinchot National Forest, Pacific Northwest Region, USDA Forest Service.Vancouver, Washington.

182

ARTHUR MCKEE ET AL.

TABLE 6.1AREAL ESTIMATES OF HABITATS IN THE DEVASTATED AREA AROUND

MOUNT ST. HELENS, SEPTEMBER, 1980

HabitatArea(ha)

Sourceof estimates

Blowdown zone 35,000 2Blown-down forest 21,000 1Clearcuts 14,000 3

Scorch zone 11,600 2Scorched forest 9,600 2Clearcuts 2,000 3

Pyroclastic flow 1,000 5Debris flow 7,100 4Mudflows 5,600 2Crater 700 2

Total 61,000 1 and 2

'Source of estimates: 1. USDA Forest Service 1981a; 2. estimated from Post EruptionConditions Map in USDA Forest Service 1981b; 3. computed as the differencebetween values given in the above two references; 4. estimated from map in U.S.Geological Survey et al. 1981; 5. estimated from map in unpublished manuscript byN. C. Banks and R. P. Hoblitt, 1981, U.S. Geological Survey, Denver, Colorado. Onlythe area of the mudflows within the boundaries of the Post Eruption Conditions Map isgiven.


TABLE 6.2MEAN PLANT COVER AND NUMBER OF TAXA PER TRANSECT IN

CLEARCUTS, BLOWN-DOWN FOREST WITHOUT SNOW,AND SCORCHED FOREST IN SEPTEMBER, 1980

HabitatNumber of

transects

Cover (%)Number of taxa

per transect

Mean Range Mean Range

Clearcut 13 3.8a 0.0-17.2 6.2 b•c 0-15

Blown-down forestswithout snow 13 0.2a 0,0-0.66 3.7 c 1-8

Scorched forests 3 0.4 0.2-0.5 4,7 b 3-7

aSignificantly different at 0.05 according to a paired 1-test,bSignificantly different at 0.10 according to a paired 1-test.cSignificantly different at 0.01 according to a paired 1-test.


SEPTEMBER, 1980, IN BLOWN-DOWN FORESTS WITH AND WITHOUTSNOWPACK ON MAY 18, 1980

Number of taxaCover (%) per transect

Number ofHabitat transects Mean Range Mean Range

Blown-down forestswithout snow 5 0.06a 0.04-0.08 2.6 1-4

Blown-down forestswith snow 6 3.3a 0.2— 10.1 8.0 2-21

aSignificantly different at 0.05 according to a paired 1-test.

zO

a.

0zcn

0

0z

Ocx

Tr 0czi

Y0

;JoG

r

FGar

(A-

71 13 5c

"'"

c 33 ,11

O N —c 0

0 0

7,C 0:1

z

<

oo

36

seS

›'

Z

z

0

2

0

zLs4

O

Ot--00:0101,1t--0000C0t---cc, CNI

0000v1000 —• 00 st) CNI 0,1

— ce)

7:000u1001•004C000010C4

0 0 C: 010 xe) -0 •-• CeS ciD

Cs: -0. Le) •-•

C.1 I.; 50

1 Xi ..c C.)I-ca =0

8 ..;

— _i -48,..,c1bi) e

7,1 -= z!g -5, I -J ,.s e

F C 1 _i -1 I " E E E1., ..: .cco g ..,

z i:-.—4z

R 61 -2 `s" a.-dh -c

4 4',3 0 g z

.Q... ". -az -4 E a E 4

- '.,n v c3R g 43,.. 44. tUti .C.1

'4-07....•

_c0: 7,

.-,g t 2 cg ,s,.

''' C3C-7 4.1C:

- 4a. EL.:.

tU

.3 G I3

C

i'3C

V>

u

.0Cl Cn cD

al 0 un—

c

.. .... ....

On .. 01 CO ul

.1

..a, .., t ..,t t

e.:3 ',.; C:34.) c...)

I.. L. 1...V 2 2 217.: eaea

ciea ea eaOJ OJ 0.) 0.)

C.; C.;C'') C.;i... I.. V 0.

X. YV 1:O. a. • —

cDt--

.0 ... .., -.. Tr

-'0 32 3

Tr 39,1*

.107

C'd

c4

o at-- oo

en 00

V

h.

6

V

7

:45

V

V

•

LC

„,

C 0V

I..cei

C

V,;j —

ni an LO r-. ve1 oo c>cl 1...4" ..a, Tr Tr

m en en anf'

.=c." ce).1" ce)"1"e7IS cy,


TABLE 6.6DOMINANT SHRUBS AND HERBS ON RIPARIAN TRANSECTS IN THE

DEVASTATED AND ASHFALL AREAS, SEPTEMBER, 19802

Cover (%)

Stratum and taxa Devastated area b Ashfall areaTall shrubs

Acer circinatum Pursh 0.1 12.1A. macrophyllum Pursh tb 6.5Alnus rut7ra Bong. t 2.7Cornus stolonifera Michx. t 2.2Low shrubs and herbs

Festuca subulata Trin 0 1.7Gymnocarpium chyopteris (L.) Newm. t 1.4Heracleum lanatum Michx. 0.1 0Ptericlium aquilinum (L.) Kuhn 0.3 0Rubu.s pannflorus Nutt. t 5.4R. spectabilis Pursh 0.4 3.8R. ursinus Chain. & Schlecht. 0 3.3Stachys cooleyae Heller t 1.9Tiarella unifoliata Hook. t 1.3Tolmiea menziesii (Pursh) T. & G. 0 1.3aDevastated area had 3 transects and ashfall area had 2 transects. All taxa with > I% coverin the ashfall area and > 0.1% cover in the devastated area are included.bt = trace cover (>0.1%).

TABLE 6.7RIPARIAN PLANT COVER BY MICROSITE IN BLOWN-DOWN FORESTS

IN THE DEVASTATED AREA, SEPTEMBER, t 980a

Microsite

Total plant cover per transect number (%)

345 346 347 MeanStreambanksAreas

18.6 0.2 13.3 10.7under elevated logsRootwads

3.4 1.2 0 1.6and tops of logsBars

13.2 2.5 1.2 5.6and overflow channelsIntact

3.0 0 0.3 1.1tephraActive channels

1.70

0.30

0.20

0.70

aThe unweighted means for the three transects, which differ in area, are given.



THREE ZONES AROUND META LAKE, SEPTEMBER, 1980

Zone Cover (%) Number of taxa per transect

Emergent 12.4 3.3Scrub shrub 4.7 5.5Forest 0.2 2.0

TABLE 6.9MEAN COVER OF IMPORTANT TAXA IN THE SHORELINE TRANSECTS

AROUND META LAKE, SEPTEMBER, 1980a

Zone b and taxa Cover (%)

EmergentCarex aquatilis Wahl. 9.2Mosses 1.1Sa/ix spp. 0.7Vaccinium ovalifohum Smith 0.7

Scrub shrubAlnus sinuala (Regel) Rydb. 1.7Menziesia fm-ugmia Smith 1.2Trautvetteria carat:Meru-is (Walt.) Vail 0.7

ForestAfries orriatzias (Dougl.) Forbes 0.2Lichens 0.6

aAll taxa with more than 0.5% cover in emergent and scrub shrub transects and all taxain the forest transect are included.bEmergent zone had 3 transects, scrub shrub zone had 2 transects, and forest zone had1 transect.

TABLE 6.10MEAN COVER OF SHRUBS AND HERBS IN THREE ZONES ON THE

TRANSECTS AROUND THREE SIDES OF META LAKE, SEPTEMBER, 1980

Zone

Cover (%) (shrubs/herbs)

South shore North shore West shore

EmergentScrub shrubForest

2.2/0.155.9/2.0

2.3/28.60.5/0.5

0/0

0/0. 1a

a— indicates no data available.

1987. In: Bilderback, David E., ed. Mount St. Helens 1980:botanical consequences of the explosive eruptions. Berkeley,CA: University of California Press.

Reproduced by USDA Forest Service for official use.

6 First-Year Recovery of Upland and Riparian Vegetation in the...

Documents

Transcript of 6 First-Year Recovery of Upland and Riparian Vegetation in the...