Definition of Ecological Succession
Ecosystems are not static. The living components drive change. Plant dominance fluctuates. Once-ascendant species decline. New species are introduced. Human activities also shape communities. What were grasslands at one time may become a forest years later. As succession occurs, each stage on the path to stability has its own species composition and community structure. Does this Spark an idea?
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Significance
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Barring human influence, ecological succession occurs in stages. The classic theory of succession was developed by F.E. Clements in 1916. Clements defined the steps of succession from a bare site that he called nudation, through establishment of vegetation and shaping of the environment by plants, to stabilization. The end result was the climax.
Later theories challenged Clements. The ecosystem concept viewed succession as driven by a maturing of the community to a state where balance of energy flow is achieved. Another theory, the population concept, argued that change occurs because of population dynamics. Chance figures into the process of change. As the environment changes, so too does species composition.
Types
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Succession occurs in any ecosystem. An example in a terrestrial community is the succession of an open field to forest. Changes in the environment necessitate change in the community. In an aquatic example, water flow patterns may change over time, allowing silt to build up. Eventually, colonizing plants like cattails, reed canary grass and sedges may take hold. The pond is no longer a pond, but a marsh.
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Identification
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C. Keever's 1950 study provides a classic example. Keever documented the succession of an old field. After the crops were abandoned, crabgrass, dormant in the soil, took hold. Over time, other colonizing plants dominated. Crabgrass was replaced by white aster and ragweed, both aggressive. Perennial plants crowded out the annuals. Pine trees then took root. However, changes in the soil prevented the pines from regenerating. Eventually, hardwoods became dominant. The former field had reached a point of maturity or sere.
Considerations
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In classic ecological succession, there is no human involvement. Communities respond by reacting to change. Human activities can often cause change too quickly for communities to adapt. In the aquatic example, runoff from an increase in impervious surfaces can cause silting that is so rapid that species cannot adapt to it.
Benefits
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As long as the species composition and community structure remain relatively the same, stability will prevail. Stability does not replace change, however. Rather, the rate of change slows over time. A stable environment can accomodate regeneration or replacement of species as long as the energy balance remains the same.
Conclusion
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Change is constantly occurring in the environment, whether from human activity, climatic change or actions of the community itself. Its plants and animals adapt or not. Species composition may regenerate or be replaced. Over time, despite the dynamic nature of the environment, stability and a slowing of change are possible.
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References
Resources
- Photo Credit Fred Fokkelman: stock.xchng
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