Succession
Succession is defined as the slow orderly progression of changes in community composition that takes place through time. Glacier Bay national park provides a prominent example of how ecological succession takes place.The bare and mineral-poor soil of the glacial moraine that was exposed as the glacier receded, had a very high pH providing uninhabitable conditions for most plants. Lichens were the only organisms able to populate the area and their acidic secretions thickened the accumulation of soil and reduced the basic pH. From this point mosses were able to colonize and add more nutrients to the new soil. The moss provide a nutrient-rich enough soil for alder shrubs to take root. These alder shrubs have symbiotic bacteria that play a vital role in fixing the poor nitrogen levels in the atmosphere and also further reduce the basic pH with their acidic leaves. After the nutrient poor environment has been mended, spruce trees grow and dominate the shrubs producing a dense spruce forest. The succession that occurred in Glacier Bay Alaska is an example of primary succession rather than secondary succession. In primary succession the plants and other organisms grow and inhabit a previously uninhabitable region, such as those covered by glaciers. Secondary succession is when an area that was previously inhabited by organisms is disturbed and then inhabited. The diagram below gives a visual representation of the succession that took place in Glacier Bay.