The Sleeping Bear Dunes National Lakeshore on Michigan's western shore is a remarkable example of succession. These dunes are giant mounds of sand that are constantly changing as the winds come off of Lake Michigan blowing the coastline sand up and over the existing dunes. This wind erosion slowly recedes the coastline.
The dunes are stabilized when grass and other vegetation grow on the dune. When areas of exposed sand form, such as with a trail, the dune becomes destabilized and strong winds may cause large, bowl-shaped areas of sand called blowouts. The sand from a blowout may cover other vegetation on the leeward side of the blowout. According to the August 29, 2006 article, " Sand Dunes," by the U.S. National Park Service, "When you are on the Sleeping Bear Plateau, you can also observe hills of sand in great crescent shaped waves that have moved inland over time covering forests in front of them and exposing skeletal forests, killed hundreds of years earlier by the moving dunes, behind them."
Ecological Succession and Natural Disasters
Brooker et al., describe succession as, "the gradual and continual change in species composition and community structure over time." On a sand dune, for example, grass begins to grow creating a more stable dune. This allows other plants to take root and spread throughout the dune.
In other types of soil, the first plants to colonize an area may not only make the terrain more stable, but may also change the soil content so that different types of plants can grow in that area. The soil composition may continue to change until the first type of plants can no longer survive in that area, and are replaced by plants that thrive in that soil composition.
On a sand dune, a blowout may occur and the whole process of succession will begin again. This is just one example of a natural disturbance. Natural disasters caused by hurricanes, glaciers, volcanic eruptions, and other strong forces of nature may completely destroy a community. The process of succession may duplicate itself as it does on the dunes; however, if the soil composition is different than it was when it was first colonized, different plants will colonize the area and the new community may be radically different.
Primary Succession and Secondary Succession
Cain et al. explain that there are two types of succession based on how the process begins. "Primary succession involves the colonization of habitats devoid of life, as we see on the Pumice Plain on Mount St. Helens, or because they are newly created habitats, such as volcanic rock. Secondary succession involves the reestablishment of a community in which most of the organisms have been destroyed." The blowouts on the Sleeping Bear Dunes are an example of secondary succession. A blowout removes all of the life in a small area, and the grass surrounding the blowout eventually covers the whole area. This creates a more stable environment in which other plants may grow, such as bearberries.
Some communities are thought to reach a climax stage, where the community composition remains relatively unchanged until a disturbance occurs, like a volcanic eruption. This may not completely destroy a community, but it may send the community into an earlier stage of succession.
It is questionable whether communities can ever achieve the climax stage. The Sleeping Bear Dunes continue to exhibit earlier stages of succession in a harsh environment. Visitors may hike through the dunes and witness the blowouts and the beginning stages of secondary succession as well as more advanced stages with berry bushes and cottonwood trees.
Reference
Brooker, Robert J., Widmaier, Eric P., Graham, Linda E., and Stiling, Peter D. Biology. New York: McGraw-Hill, 2008.
Cain, Michael L., Bowman, William D., Hacker, Sally D. Ecology. Sunderland: Sinauer Associates, Inc., 2008.
Diane Ursu - Diane Ursu joined Suite101 as a contributing writer in August 2009 and became a Feature Writer in January 2010. She is a freelance writer ...
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