Exit Glacier Retreats
0 Years

Exit Glacier Retreats








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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Lichen and Mosses 
Grow on the Exposed Rock
1 Year Later

Lichens and Mosses








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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Small Shrubs Begin to Grow
3-30 Years Later










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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Willow, Alder, and other Small Trees
26 - 45 Years Later

Willow Trees










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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Birch, Cottonwood, and other Deciduous Trees
45 - 100 Years Later

Birch Trees










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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Black Spruce, White Spruce, Hemlock
100 - 350 Years Later

Black Spruce









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.


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