What Is Ecological Succession?
There is a concept that has developed in the community of professional ecologists that is called ecological succession. This refers to a change in the species structure in a given ecological community over time. This change is generally, though not universally, discussed in terms of an observed change. The causes and types of ecological succession are discussed below.
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Cause
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Ecosystems are not static. They are dynamic environmental systems that are subject to alteration. For any given species, be it plant or animal, there are environmental conditions that will allow that species to thrive. If those conditions remain static, those species would continue to thrive. Ironically, the presence of those very species--not to mention other natural forces and human intervention--can all serve to alter the environmental conditions such that those species can no longer thrive, but other species can thrive.
Primary Succession
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One type of succession is called primary succession. Primary succession occurs when all previous living organisms have been removed from an area. A lava flow, intense wildfire, or glaciation can leave an area in this uninhabited state. At this juncture, organisms entering into the uninhabited area begin the process of primary succession. It typically entails simple plants, such as lichens and mosses, overtaking the area. Over time, as the simple plants change the soil, progressively more complex species move into the area with each, in turn, largely displacing the formerly dominant species.
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Secondary Succession
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The other major form of ecological succession is referred to as secondary succession. Secondary succession is also set in motion by a disturbance of the environment. These disturbances are insufficient to complete wipe out the previously existing species, but may include windstorms, some less intense wildfires and defoliation due to insects. In this case, previous species of plants will re-sprout and start the cycle over somewhere in the middle. Again, species will progressively replace one another as the system matures.
Climax Communities
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The relative end point of ecological succession is what is called a climax community. The climax community is an environmental system in which there is very little or extraordinarily slow change. An old growth forest is a good example of what ecologists consider a climax community. It is important to realize that these climax communities are subject to change. There is a process called microsuccession in which small variances in the system lead to small changes.
Considerations
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Humans both influence and are influenced by the process of ecological succession. Almost every human intervention from clear cutting and over-hunting to farming and pollution can all set ecological succession into motion. Every human intervention alters the environmental conditions, effectively creating situations in which different species can dominate. These new conditions tend to be such that they invite in rapid growth species like weeds. In turn, human beings are required to expend considerable time and energy managing the changes they set in motion.
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