Multimedia Mania/abacus-multimedia-mania.iso/dp/0100/01000.txt

Text File | 1993-07-27 | 21KB | 351 lines

$Unique_ID{bob01000}
$Pretitle{}
$Title{Glacier Bay
Post-Glacier Plant Succession}
$Subtitle{}
$Author{Kirk, Ruth}
$Affiliation{National Park Service;U.S. Department Of The Interior}
$Subject{ice
glacier
inlet
spruce
forest
high
alder
bay
plant
plants
see
pictures
see
figures
}
$Date{1983}
$Log{See Harebells & Fireweed*0100001.scf
See Lituya Glacier*0100002.scf
}
Title:       Glacier Bay
Book:        Part II: Of Time And Ice
Author:      Kirk, Ruth
Affiliation: National Park Service;U.S. Department Of The Interior
Date:        1983

Post-Glacier Plant Succession

In Muir Inlet

     A photograph taken in the 1890's shows an excursion steamer at the Muir
ice front and, perched close by on a completely barren moraine, the one-room
cabin where John Muir hosted Harry Reid's research party.  Today the cabin is
just an overgrown heap of chimney stones and from the place where the photo
was taken you can't even see out through the alder and spruce.  As for the
glacier snout, it's now 40 kilometers (25 miles) away. Just as glaciologists
find these inlets ideal for pinpointing the coming and going of ice, botanists
revel in the chance to document the plants' green conquest of denuded
landscapes retreating glaciers leave behind.

[See Harebells & Fireweed: Harebells (front) and fireweed push up their colors
from streamside rock rubble tumbled like fist-sized gems by past torrents of
glacial meltwater.]

     My husband, Louis, and I were at the Muir snout this afternoon with Chess
Lyons, aboard our small sloop, Taku.  At 7 meters (23 feet) long, Taku is
outclassed by some icebergs we sailed among.  We brought the sloop to Juneau
by ferry and then sailed and motored to Glacier Bay.  Louis is a skilled
sailor so enamored of the sea that I suspect saltwater, not blood, flows in
his veins.  Our friend Chess has no sailing background but his career as
naturalist with British Columbia Provincial Parks - he is now retired - and
maker of nature films has given him abundant outdoor experience.  I am adept
in the galley, less so in the cockpit, yet enthusiastic about life afloat,
whether aboard Growler last month or now Taku.  We ate today's lunch while
sailing up the inlet, wind flicking salad from our bowls.  Even without sails
raised, Taku heeled ten degrees.  With sails, we traveled faster than Taku's
rated hull speed of seven knots.

     Yesterday we motored to the head of Wachusett Inlet, a Muir tributary.
The lower part of Wachusett Inlet, longest free of glacier ice, is green with
vegetation while utter barrenness still characterizes the newly ice-free upper
reaches.  At the head of the inlet we hiked to the divide separating Wachusett
from Queen Inlet.  This took us backward through vegetation's green
chronology: The lower the slope, the more recent the plants.  Hiking at first
was like crossing a desert alluvial fan except that we found no plants.  Even
in Death Valley you can't take a dozen steps without coming on greenery.  Here
was nothing but sand and rock.  The land is virgin, newly released from the
ice.

     A bit higher I finally noticed a plant, a single fireweed half a finger
high.  Soon other fireweed plants and equally tiny willows were present.
Upslope the plants gradually got taller and the willow even had branches.  We
added scouring rush to the species list we were keeping, then dryas.  The
dryas stood a centimeter (0.4 inches) high, each plant having six leaves.  I
kept the lens cap on my camera because the plants were so widespread and puny
that footsteps kicked up dust.

     The vegetation changed abruptly as we reached a high terrace that had
been free of ice substantially longer than the slopes below.  The willow now
reached halfway to our knees.  leathery-leaved dryas plants formed circular
mats, and cushions of dark, dry moss padded spaces between alders growing as
high as my shoulder.  At the divide we found Christmas tree spruce and carpets
of heather.  We had walked backward through plant succession, beaching our
dinghy on land born just two years ago and climbing to a surface now green,
but new a century ago when Harry Reid made his glacier map and John Muir
explored the inlet that bears his name.

     Plant beginnings may be no more than "black crust," a cohesive feltlike
nap believed to be mostly algae.  This helps stabilize silt and hold in
moisture.  Moss adds thicker, more conspicuous tufts to the covering, and
windblown spores and seeds of plants from scouring rush to fireweed and
willow, spruce, and alder arrive and root.  Along beaches, seeds such as those
of ryegrass ride ashore on extreme high tides.  Blueberry and crowberry seeds
get deposited in bird feces, the seedlings thereby benefitting from minute
dots of fertilizer.  Bears and wolves and mountain goats, shaking water from
their pelts, may shake out clinging seeds picked up where they last fed.
Campers sweeping out tents may also contribute.  By such means, vegetation's
green conquest makes its start.

     Successful growth depends in part on where the seeds happen to land.
Glacier till and outwash are notoriously deficient in nitrogen and at first
produce this stunted, yellowish plant growth.  Green exceptions to rule are
alder and dryas.  Both solve the problem by associating with micro-organisms
that draw nitrogen directly from the air.  Alder relies on molds living on its
roots in nodules about the size of grain kernels or as sometimes big as
walnuts.  Roots apparently interrelate with mycorrhizae, minute fungi that
sheathe the roots of many plant species and stimulate growth in ways not fully
understood.  The process seems to involve enzyme and nitrogen production.

     Fossil leaves, seed hairs, and pollen recovered in bogs and excavations
indicate that dryas pioneered much of northern Europe and America at the close
of the last Ice Age.  Their first year the plants produce single rosettes of
tiny leaves.  The next year this growth triples; the third year it quadruples.
Mats well over a meter (a yard) across develop after five years.  At this
stage, lateral shoots rapidly fuse individual mats into massive carpets.

     Sitka alder (Alnus crispa) begins to dominate suitable sites within a
couple of decades following glacier retreat.  It eventually forms dense stands
that are abominably tangled and disliked by humans who are afoot.  At this
stage trees are about 3 meters (10 feet) high, the limbs of individual alders
growing low and wickedly interlocked.  Hike through such thickets and you find
arms, legs, shoulders eyeglasses, bracelet, and backpack each caught
separately and pulled in differing directions.  You can't see out.  Holding to
a course is largely luck without a compass.  Brown/grizzly bear tracks thread
what openings there are, then vanish.  The more you try to see where the
tracks lead, the more certain it is that your noisy bashing about will startle
a ptarmigan, the explosive whirr of its wings all but stopping your heart
until its gravelly tobacco-tobacco-tobacco call registers an all-clear: bird,
not bear.

     "Two of us after three hours of thrashing through this dreaded shrub,
emerged at the point where we had set out!" lamented a recent British
researcher.  But alder has its good side.  It stimulates the growth of other
plants.  Its fallen leaves put as much nitrogen into the soil as alfalfa
would.  Dryas similarly enriches the soil.  Alder and dryas are such
successful plant pioneers and become so dominant that you'd expect them to
last forever. Their growth is so dense, however, that their own progeny can't
make headway. Their role is to stabilize and enrich the soil.  That done, they
die out and a comparative explosion of plant diversity ensues.

     Overall, this successional drama is similar along the shorelands of all
up-bay country.  First come the scattered pioneers, succeeded by a low-growing
mat stage and then a thicket stage.  The two major arms of the Glacier Bay
waterway differ, however, in their rates of development within these stages
and in the species playing key roles.  In Muir Inlet and its tributaries alder
is ubiquitous.  In the upper Tarr Inlet drainage alder thrives only in swales
and draws.  Soapberry and willow approximate a thicket stage, one you can
easily hike through.

     These geographic differences are surprisingly clear cut.  In Muir Inlet a
land surface that has been free of ice nearly a century will host a formidable
tangle of alder - or be well along toward spruce forest.  But in Tarr Inlet,
dryas and willow still will dominate a surface of comparable age.  Why should
Muir Inlet be ahead in its plant sequences?  Probably because it opens toward
the prevailing southerly wind.  This may simplify the arrival of seeds and
spores, and moderate temperatures.  Harsh Tarr Inlet conditions contrast
markedly.  Ocean-born moist winds are blocked by the Fairweather mountains,
which send cold, dry air draining downslope from the high peaks.

     From Growler, we regularly rowed ashore so that Emily Chase could core
trees for a study, counting annual rings to find out how long it takes for a
surface freed of ice to become upholstered by full forest.  In the park,
Bartlett Cove, which is edged by a Little Ice Age terminal moraine, has been
evolving toward forest the longest.  It melted out a bit before Captain
Vancouver arrived offshore.  Its forest now is a stately mix of Sitka spruce
and western hemlock.  The forest floor is thickly padded by moss and clubmoss
and is studded with fern, blueberry, devil's club, and twayblade.

     On Young Island, only a few kilometers up the bay from Bartlett Cove and
therefore free of ice only about two centuries, we sank ankle deep into
chartreuse moss which extended from the forest floor onto the stubby lower
branches of spruce.  The trunks of these trees were bigger than one person
alone could encircle with outstretched arms.  The only hemlock we happened to
find had a diameter less than half that of most of the spruce.  On Francis
Island, spruce were mere dark pyramids barely beginning to overtop thick
cottonwoods, and we saw no hemlock.  There, we pulled ourselves up steep
slopes by alder and willow branches.  We had moved 30 kilometers (19 miles)
up-bay from Bartlett Cove, sampling forests separated by about twelve decades
of growth opportunity.

     Spruce arrive and sprout early in Glacier Bay's plant sequence, but they
grow slowly at first.  A 30-to-40-year-old tree may stand only knee high yet
have a trunk as thick as a man's ankle.  Its time is coming.  Eventually it
dominates for a century or two, then is outnumbered by hemlock, providing
events follow a classic course for plant succession here.  On the outer coast,
however, not all spruce forests even wait for the ice to melt.  The forest
actually grows like a green rug atop the stagnant Fairweather Glacier tongue
and on remnants of the Lituya Glacier, flourishing because lowland glaciers
characteristically carry heavy mineral loads.  Spruce and even good-sized
hemlock stand rooted in thick soil and duff.  But they tilt drunkenly because
pits form in the underlying ice and meltwater grottoes collapse.

     Muskeg is the final stage of plants' green conquest in southeast Alaska,
though none exists along Glacier Bay National Park and Preserve's inner
waterways.  Sufficient time has not elapsed since withdrawal of the Little Ice
Age glaciers.  Muskeg represents a wondrous coming full circle, a return to
openness though not to barrenness.  It develops as forest soil deteriorates
after 500 to 1,000 years, building a hardpan layer that blocks drainage and
prevents roots from anchoring securely.  Mature trees consequently topple
readily during wind storms, creating openings which encourage other plants.
Saturated conditions preclude most bacteria and fungi, retarding decay.
Instead, sufficient organic litter accumulates to hold year-round moisture
even without the hardpan layer, which slowly disintegrates.  Acid conditions
prevail and vegetation changes from forest to muskeg.

     Along the park's outer coast are lowlands that escaped being covered by
ice during the last glacier advance.  They have been muskeg for at least 8000
years, changing very little through most of this time.  New species
continually arrive and vie for optimum position during the two or three
centuries that lead up to the spruce-hemlock stage.  But once muskeg takes
over, little changes.  Spruce and western hemlock continue, but grow scattered
and dwarfed and with a look of great age and adversity.  Mountain hemlock,
lodgepole pine, and in places yellow cedar, come in.  Beneath them a variety
of soggy and leathery-leaved species forms a rough upholstery.  The mood of
muskeg is elfin, mysterious.

     Just east of Glacier Bay, muskeg grows at Point Couverden, the Home Shore
that gave refuge to Tlingits fleeing the Little Ice Age glacier encroaching
upon their Valley of the River Grass.  En route from Juneau Louis, Chess, and
I anchored Taku overnight in the point's lee and I rowed ashore. Walking
inland I passed first through beachside ryegrass and head-high cow parsnip
flower stalks left from last season.  Then I passed through a band of
spruce-hemlock forest rich with fern.  Ahead I could see the rounded tops of
lodgepole pine, a clear contrast to the sharp spires of spruce and the
pointed-but-drooping tops of hemlock.  Abruptly, the forest gave way to open,
mossy, soggy muskeg.  Pines grew scattered and interspersed with a few stunted
mountain hemlock.  Deer fern replaced the lady fern and wood fern I'd noticed
in the forest, and hip-high bushes of bog laurel and Labrador tea mixed with
enormous blueberry bushes laden with fruit the size of giant peas.  I could
pick five or six powdery-blue berries at a time without moving my hand.  For
the first time I can remember it didn't matter if a berry dropped.  We had
blueberry pancakes for breakfast.

Tidal Inlet

     The wind has died.  Louis and Chess and I are motoring up Tidal Inlet in
Taku, savoring the last of the daylight.  Waterfall Fjord would be an
appropriate name here.  Every few minutes we come to another falls.  Most
spill over the cliffs, unnamed and rarely seen.  Ribbons of white, cascades,
plumes.  One as lacy as Yosemite's Bridal Veil Falls, deep-set in a rock vee.
Another showy only at the bottom, where it splashes from six separate ledges.
A third hits so hard it spurts up and out.  From the side you see only an odd,
gravity-defying spout of white water.

     High above us, the fjord wall is gashed by a raw arc, the scar of a
gigantic landslide, that stretches for more than 2 kilometers (1 mile) and
looks as high as a six- or eight-story building.  It is ten times that.

     Austin Post once told me the scar formed as ice choking the inlet
retreated, withdrawing support and leaving an over-steepened slope.  This
probably happened around 1860-70.  Parts of the scar have stabilized enough
for alders to grow, but the whole slope looks poised to slide more - and it
probably does slide a little whenever there's an earthquake.

     We cruise along sipping brandy aboard Taku and contemplating earth forces
capable of suddenly resetting the clock of life's sequences.  Were this slide
to let go and crash into saltwater, a stupendous wave would strip vegetation
far beyond reach of the slide itself.  That happened at Lituya Bay in July
1958.  A quake along the Fairweather Fault, at the upper end of the bay,
dislodged rain-soaked rubble from a steep headwall.  This material sheared off
ice at the snout of the Lituya Glacier, then, riding an air cushion, shot
across the toe of an adjacent cliff to an elevation of 525 meters (1,700
feet).  The force hurled icebergs and seals onto high ledges and violently
uprooted mature spruce.  Displaced water rose as an incredible wave that
ravaged shores even at the mouth of the bay, 11 kilometers (7 miles) from the
headwall.  The wave lifted a fishing boat, swept it across the moraine
guarding Lituya Bay's entrance, and smacked it down in the ocean so forcefully
the seams burst and the boat disassembled, fortunately not before the couple
aboard could leap into their skiff and row off.

     From the air the devastated Lituya Bay cliff scar is astonishing.
Uprooted trees litter every beach of the bay.  Seen from a boat, the
destruction appears even more dramatic.  Its full magnitude is immediate,
without the detachment a plane affords.  The soil, forest, glacial till, rock,
and ice that slid into the water is estimated at nearly 400 million cubic
meters (1.3 billion cubic feet).  This appalling mass sent a wave racing
down-bay probably 250 kilometers (155 miles) per hour and exerting sufficient
pressure to splinter trees and rip mussels and barnacles from their holds.
Lituya Bay shorelands for a kilometer (half mile) inland still have recovered
only to the alder stage.

[See Lituya Glacier: Lituya Glacier - A 1958 earthquake triggered a landslide
at Lituya Bay's upper end. The slide created a wave that denuded the
promontory facing it to an altitude of 525 meters.]

     Four earlier giant waves - 1936, 1899, 1874, 1854 - can still be traced
by tree damage.  Heights ranged from some 20 meters (65 feet) to about 130
meters (425 feet) gentle foretastes of July 1958.  Doubtless there have been
others, and giant waves remain certain for the bay's future, perhaps soon.
Slopes where the 1958 slide broke loose are still unstable and a separate huge
inverted vee of unconsolidated earth hangs on a cliff near the North Crillon
Glacier.  This new headwall slippage already seems to defy gravity.

     Bedrock geology is responsible for such slippages.  The 1958 quake
registered eight on the Richter scale and produced a 7-meter (23-foot)
horizontal displacement along the Fairweather Fault.  With the edge of the
oceanic plate slipping beneath the continental plate and wrinkling the edge
into mountain ranges, earthquakes are inevitable.  Given the walled-in nature
of fjords, so are the consequent devastating waves.  The shifting along the
junction of the oceanic and continental plates is a tectonic ("building")
process.  The Earth's crust is built of adjoining plates which float on a
molten core.  Uplift of the coast comes in jerks.  Barnacles still cling where
bellflowers and Indian paintbrushes bloom.  The change from tidepool to cliff
garden can be abrupt.

     The coming and going of glaciers can also directly raise and lower both
the ocean volume and the land surface.  Worldwide sea level during the
Wisconsinan Ice Age stood about 100 meters (325 feet) lower than it does
today.  It rose as the glaciers melted and released water to the oceans.  If
Earth's ice were all to melt, sea level would rise far more.  Fish would swim
Tokyo's Ginza.  Sea anemones would wave from Manhattan's World Trade Center.

     Evidence of sea-level fluctuation along the park's outer coast includes a
wave-cut terrace 30 meters (100 feet) above present tide line.  Because the
terrace is recognizable on both sides of the Fairweather Fault, tectonic force
cannot explain its origin.  Most likely it formed during sea-level changes
produced by glacier ice.  Ice a kilometer or two (0.5 or 1.3 miles) thick is
enough to depress bedrock.  Melting releases this weight, and the land slowly
rebounds or rises.

     In Glacier Bay, the rate of rebound is greater than anywhere else in
southeast Alaska, and even by worldwide standards it is spectacular.  At
Bartlett Cove rebound now produces a 4-centimeter (1.5-inch) rise per year. On
the nature trail near the lodge, where you drop down the stairs from mature
spruce-hemlock forest into a zone of young spruce and beach meadow, you step
onto land newly raised from the sea.  The base of the stairs marks the old
high tide line.  Count a sapling's growth rings, then add time for salt to
wash from the beach and for spruce to germinate, and you can know about how
long ago the surface changed from sea bottom to dry land.  Up-bay, release
from the weight of the ice is more recent than at Bartlett Cove and present
rebound is even more rapid.  The shorelands rising fastest now are those close
to the mouth of Muir Inlet, where glacier retreat began only about a century
ago.

     With rebound, islands expand noticeably, decade by decade, and shoal
water shifts, quickly rendering inshore marine charts useless.  Tide zones and
beach meadows are constantly born anew.  And humans experience certain
dilemmas.  For example, the land has risen so decidedly that National Park
Service employees now can get their boats to and from the headquarters dock
only when full high tide floods the channel.  At Gustavus, the politics grow
tangled, for who owns virgin land?  Once the gravel of these flatlands formed
the fill in Muir Inlet.  Swept southward, that gravel lay beneath the sea for
millennia.  Now the land has risen and we humans puzzle over its ownership.