whether various species of forest trees 
will show important differences in 
mortality or productivity is not yet 
clear. 
At higher elevations, snow pro- 
tected the plants beneath the canopy 
of forest trees from direct ash deposits, 
but impacts still accrued in this un- 
derstory vegetation. Many plant spe- 
cies already flattened by snow were 
trapped by heavy ash. Erosion and 
rain may eventually remove sufficient 
ash to free such plants, but the damage 
may have been too severe or too much 
of the growing season may have passed 
for them to survive. Mosses and li- 
chens, which form low mats, are the 
most severely damaged. Other species, 
such as the erect-growing huckleber- 
ries ( Vaccinium spp.), were able to 
emerge from the ash layer as the snow 
melted. These plants grew well during 
1980, probably because there was less 
competition from other plants and be- 
cause the high insect mortality re- 
duced grazing pressure. Many of these 
emergents have sent roots into the nu- 
trient-rich ash and may thus benefit 
directly from improved nutrition. 
Jim MacMahon of Utah State Uni- 
versity has shown that pocket gophers 
are major agents of ash-layer disrup- 
tion. These little burrowing rodents 
improve soil aeration and water in- 
filtration. As a consequence, minerals 
from ash are more rapidly incorpo- 
rated into the soil, where they can 
be used by plants. Silviculturists nor- 
mally view pocket gophers as unmiti- 
gated pests because they eat young 
conifers, but for the next few years, 
gophers may prove valuable allies in 
the reestablishment of tree seedlings 
in clear-cuts and blowdown areas. 
For most plant species, recovery in 
heavily ashed areas will be rapid. 
Young Douglas firs, silver firs, and 
noble firs ( Abies procera) may suffer 
heavy mortality, and species of li- 
chens, mosses, and other low-growing 
plants will be disproportionately rare 
for many years, but overall forest pro- 
ductivity should soon return to pre- 
eruption levels. When nutrients from 
the ash, such as phosphorus and po- 
tassium, are added to the soil, they 
may actually generate a pulse of en- 
hanced productivity. Understanding 
the differential effects of Mount St. 
Helens’ ash deposits on vegetation will 
improve the ability of ecologists to 
read the history encoded in tree rings, 
pollen records, and soil profiles in 
other volcano-dominated ecosystems. 
Less apt to survive than trees that 
were primarily subjected to ash de- 
posits are the scorched conifers found 
in a narrow but expanding band be- 
tween green timber and standing dead 
trees. Many trees in this border zone, 
such as western hemlock ( Tsuga het- 
erophylla), Douglas fir, and noble fir, 
survived the initial surge of heat and 
gas from the main eruption but were 
weakened by it and also received 
heavy ash deposits. During the dry 
summer, many trees gradually suc- 
cumbed from internal heat or other 
factors. Fortunately, young saplings 
beneath many of these trees escaped 
virtually unscathed by virtue of the 
snow pack present during the eruption. 
Thus, the next conifer generation is 
already well established and should 
experience a burst of growth now that 
the saplings are released from com- 
petition with their parents. 
Still closer to the volcano, where 
stands of large trees did not survive 
the first blast, stark contrasts appear 
between areas that had been clear- 
cut shortly before the eruption and 
areas that had been covered with for- 
est. In most parts of the blowdown 
area, snow again offered some pro- 
tection to ground-layer vegetation, and 
terrain closest to the mountain re- 
ceived less ash than more distant areas 
directly in the path of fallout. In the 
clear-cut areas, regeneration of her- 
baceous vegetation began shortly after 
the eruption. Species that commonly 
grow on recent clear-cuts, such as 
fireweed ( Epilobium angustifolium), 
pearly everlasting ( Anaphalis margar- 
itacea), and bracken fern, have eco- 
logical characteristics distinct from 
those of forest understories. They grow 
fast, produce many easily dispersed 
seeds, and are able to colonize newly 
disturbed sites rapidly, tolerating high 
light, high temperatures, and drought. 
In contrast, areas in the blowdown 
region that were covered by deep for- 
est at the time of the eruption lacked 
herbaceous vegetation as snows re- 
turned in the winter of 1980. The for- 
est understory normally consists of 
herbs and shrub species adapted to 
cool, moist, dark conditions. These 
grow slowly; produce few, poorly dis- 
persed seeds; and are intolerant of 
high-light or high-temperature condi- 
tions. Any such understory plants that 
survived the adverse impact of the 
blast and ash layers were thus con- 
fronted with an inimical environment. 
Recovery in these blowdown areas 
will require invasion by aggressive spe- 
cies from the surrounding clear-cuts. 
As succession proceeds, conditions will 
gradually alter in favor of species 
adapted to the forest. A major pre- 
diction to be tested during the 1981 
growing season is that within the blow- 
down area, pioneer species from clear- 
cuts will make up the bulk of new 
growth in the once forested parts. 
However, since the flattened trees cre- 
ate microsites favorable to the survival 
and regeneration of some understory 
vegetation, the next forest generation 
will be fostered by the slowly decom- 
posing remains of dead trees. 
The potential juxtaposition of plants 
having markedly different ecological 
strategies offers opportunities to test 
some ecological theories. Prevailing 
opinion would predict, for example, 
that in open microsites, pioneer species 
should outcompete the forest species, 
whereas in protected sites, the reverse 
should happen. As conditions improve, 
overall dominance should rest with for- 
est species. 
The region of tree blowdown and 
its surrounding ring of moribund trees 
presents the U.S. Forest Service with 
difficult management options. Stand- 
ing dead and downed trees ameliorate 
the microclimate of the substrate, re- 
tard erosion, and foster natural suc- 
cession. Trees blown into stream chan- 
nels reduce erosion and siltation and 
promote the recovery of streamside 
vegetation and fauna. Furthermore, 
there is a widespread desire to pre- 
serve much of this region for inter- 
pretive, recreational, and scientific 
purposes. The Forest Service, which 
manages most of the affected land, 
must reconcile these factors with the 
value of downed timber and the dan- 
ger of fire or of beetle infestations 
in Douglas fir, starting in moribund 
vegetation and moving into healthy, 
economically valuable forests. Salvage 
removal of downed timber is begin- 
ning, although not in areas designated 
for detailed study by the Forest Ser- 
vice Special Planning Team. 
Flood plains are intrinsically unsta- 
ble habitats, and those in the area 
affected by the May 18 eruption will 
recover more slowly than either the 
ash or blowdown zones. The mudflows, 
which swept the lower thirty-two miles 
of the North Fork of the Toutle River, 
fifteen miles of the Muddy River, and 
many smaller streams, removed most 
of the vegetation in their path before 
settling into unstable masses. Erosion 
rates will be high, and successful seed 
invasion will be limited for many 
years. Last July I observed cottonwood 
41 
