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Exit Glacier Retreats
0 Years |
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Exit Glacier Retreats
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Exit Glacier gets lots of snow in the Winter but melts even more in the
Summer. So overall it gets less snow added to it than snow that melts away.
This causes the glacier to slowly recede up the valley. Land that had been buried
for thousands of years is suddenly uncovered. All the soil and
plants have long ago been scraped away but soon the bare rocks will
support a rich growth of plants and animals. Because plant and
animal life have to start over from bare rock we refer to this as
Primary Succession.
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Succession
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Lichen and Mosses
Grow on the Exposed Rock
1 Year Later |
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Lichens and Mosses
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After about one year, lichen and moss begin to grow on the
exposed rocks. These lichens and mosses begin to retain water and
help keep the silt and soil from blowing away.
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Succession
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Small
Shrubs Begin to Grow
3-30 Years Later |
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Fireweed
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About three years after the glacier has retreated, pioneer
plants begin to grow. Some of these plants are: Fireweed, Lupine, and Blueberry Bushes. Bees and
spiders begin to travel here to get food from these plants. These
small creatures bring seeds, caught on their bodies, to the area so that
new
plants and small shrubs begin to take root. Also, the decomposing
flowers and leaves from these plants add nutrients to the poor soil that
is starting to be seen there. This stage of succession can last up to 30
years before new trees begin taking root.
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Succession
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Willow, Alder, and other Small
Trees
26 - 45 Years Later |
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Willow Trees
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As
the small shrubs begin to die off they add lots of nutrients to the
soil. These nutrients prepare the soil for other larger
species. Soon small trees like the alder and willow begin to
reclaim the land. The shrubs and smaller trees provide the cover
and nesting that small birds, rodents, and other small mammals need.
Soon, these animals begin to live in this area. Those smaller animals attract
larger predators such as the lynx, red fox, grizzly bear, and gray wolf.
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Succession
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Birch, Cottonwood, and other Deciduous
Trees
45 - 100 Years Later |
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Birch Trees
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The
alder trees are a very important species because their leaves improve the
soil by bringing nitrogen from the air. This happens through
its leaves, down
its stem and from its roots into the soil. This added nitrogen
from the air prepares the soil for larger trees. Next, the birds
and insects that inhabit this area bring in birch and cottonwood seeds
that are trapped in their fur and feathers or dropped in their scat
(poop). Soon, these larger trees are flourishing. Their tall
trunks and broad leaves shade the smaller trees that eventually die off
and add more nutrients to the soil. Then, more small animals and larger
animals begin to inhabit this area.
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Succession
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Black Spruce, White Spruce, Hemlock
100 - 350 Years Later |
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Black Spruce
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Black
spruce, white spruce, and hemlock trees eventually take root on this
once barren land. Their large trunks raise them above the other
trees which soon die out and fertilize the soil. These trees grow
into an old growth stand or a climax forest. Even more small
animals and larger animals begin to inhabit this area.
Back to Boreal Forest
Succession
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