The initial plant community that was established within the boundaries of this plot was made up of those species that could tolerate the periodic mowing that "controlled" this "grass" ecosystem.
Soon, though, other plant species became established as a consequence of the removal of the stress of mowing. Over time, the increased shading of the soil surface and the increased moisture retention of the undisturbed soil-litter interface allowed an even greater diversity of plants to grow and thrive in the Succession Garden.
Eventually, taller, woody plants became established which shaded out the sun-loving weed community. In the coming years we expect tree seedlings to grow up within the Succession Garden and slowly establish a new section of the forest. Ecological succession is a force of nature. Ecosystems, because of the internal species dynamics and external forces mentioned above, are in a constant process of change and re-structuring.
To appreciate how ecological succession affects humans and also to begin to appreciate the incredible time and monetary cost of ecological succession, one only has to visualize a freshly tilled garden plot.
Clearing the land for the garden and preparing the soil for planting represents a major external event that radically re-structures and disrupts a previously stabilized ecosystem. The disturbed ecosystem will immediately begin a process of ecological succession. Plant species adapted to the sunny conditions and the broken soil will rapidly invade the site and will become quickly and densely established.
These invading plants are what we call "weeds". Now "weeds" have very important ecological roles and functions see, for example, the "Winter Birds" discussion , but weeds also compete with the garden plants for nutrients, water and physical space.
If left unattended, a garden will quickly become a weed patch in which the weakly competitive garden plants are choked out and destroyed by the robustly productive weeds. A gardener's only course of action is to spend a great deal of time and energy weeding the garden. This energy input is directly proportional to the "energy" inherent in the force of ecological succession.
If you extrapolate this very small scale scenario to all of the agricultural fields and systems on Earth and visualize all of the activities of all of the farmers and gardeners who are growing our foods, you begin to get an idea of the immense cost in terms of time, fuel, herbicides and pesticides that humans pay every growing season because of the force of ecological succession.
Open water such as a lake or pond eventually becomes climax woodland. Hold your mouse pointer over each image for more information or for a full explanation click here. There are two main types of succession, primary and secondary. Primary succession is the series of community changes which occur on an entirely new habitat which has never been colonized before. For example, a newly quarried rock face or sand dunes.
Secondary succession is the series of community changes which take place on a previously colonized, but disturbed or damaged habitat. For example, after felling trees in a woodland, land clearance or a fire. The Major Points: The species living in a particular place gradually change over time as does the physical and chemical environment within that area.
Succession takes place because through the processes of living, growing and reproducing, organisms interact with and affect the environment within an area, gradually changing it.
Each species is adapted to thrive and compete best against other species under a very specific set of environmental conditions. If these conditions change, then the existing species will be outcompeted by a different set of species which are better adapted to the new conditions.
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They all initiate the process of succession in communities. Aa Aa Aa. The Role of Disturbance. In plant communities, succession begins when an area is made partially or completely devoid of vegetation because of a disturbance.
Disturbances can take many different forms, and can vary in intensity and size. Large, extreme disturbances such as volcanic eruptions or glacier retreat result in very slow succession due to complete mortality of all living individuals in the system, as well as loss of the entire soil complex. This type of succession is often called primary succession, as the soil, as well as all characteristic organisms, needs to re-establish.
Large, low intensity disturbances, such as plowing in conventional agriculture, result in moderate amounts of succession, where species can survive in the soil and quickly recolonize areas after a disturbance. Early successional communities are those that establish themselves relatively quickly after disturbance, while late successional communities are those that establish themselves much later.
Classic Perspectives of Succession. Figure 1: Chronosequences are often used to study succession. A Typical chronosequence for sand dune succession. Figure 2: Two contrasting views of succession. A The super-organism concept, where groups of species are tightly associated, and are supplanted by other groups of tightly associated species.
Patterns and Mechanisms of Succession. Plant reestablishment 15 years after the debris avalanche at Mount St. Figure 4: Succession after glacier retreat. Figure 5: Keever's observed pattern of succession in North Carolina agricultural old fields. Recent Research on Succession. Recently, ecologists have been developing mathematical models to better characterize and predict successional changes.
For example, The Resource Ratio Hypothesis, proposed by David Tilman , models successional shifts in plant communities based on the assumption that succession is driven by a tradeoff in competition for nutrients in early succession, and for light in late succession.
Other researchers, such as Henry Horn have used transition matrix models and Markovian models to measure rates of succession and predict the outcomes of succession. Figure 6: Plant diversity increases throughout succession. Fields were last plowed in While the process of succession has been studied by ecologists since the turn of the 20th century, it is still very much a dynamic field of study today.
Multiple, complex mechanisms can all interact to result in predictable patterns of change in communities over time. Recently, ecologists have used principles of succession to inform the applied ecological fields of Restoration Ecology and Invasion Biology.
References and Recommended Reading Bazzaz, F. Odum, E. The Strategy of Ecosystem Development. Science , Reiners, W.
Plant diversity in a chronosequence at Glacier Bay, Alaska. Ecology 52, Article History Close. Share Cancel. Revoke Cancel. Keywords Keywords for this Article. Save Cancel.
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