Primary  succession, such as
   this sequence in Glacier Bay, Alaska, occurs where no soil exists when
   succession begins.
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<Li> Pioneering species such as mosses and fireweed build up the soil.
<Li> Shrubs such as Dryas follow.
<Li> Nitrogen fixation by Alder further enriches the soil.
<Li> Eventually a climax forest is dominated by spruce and hemlock.