The Best of the Bureau/The_Best_of_the_Bureau_Bureau_Development_Inc._1992.iso/dp/0100/01000.txt

Text File | 1992-08-07 | 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 pla