PDF Examples of ecological succession

[Pages:1]Imagine a forest that has been destroyed by a forest fire. All the plants and animals that lived there are gone. But the burned-up forest will not remain lifeless forever. Plants and animals will return to the area in a process called ecological succession.

Succession is gradual change in the structure and makeup of an ecological community over time. This can happen in an area where a disturbance destroyed an existing ecosystem. It can also happen in an area of new land where an ecosystem has never existed before. As succession progresses, new populations of organisms replace previous populations.

Primary succession occurs where no ecosystem has existed before. It is a very slow process because it begins on bare rock. A glacier that retreats leaves behind no soil. Lava from a volcanic eruption hardens into bare rock. Primary succession begins with soil formation.

The first stage of succession involves pioneer species. In primary succession, pioneer plants are those that can grow without soil, such as lichens. Lichens begin breaking down a rock. Seasonal cycles of freezing and thawing form cracks in the rock. The dead remains of lichens and dust fall into the cracks. Mosses may being to grow. When mosses and lichens die, they form parts of soil. Slowly, enough soil forms for small shrubs to grow. The roots of the shrubs break up more rock and more soil forms. Larger plants are able to grow. Eventually, a mature community exists where once there was only a bare rock.

Primary succession has been recorded at Glacier Bay, Alaska, as a glacier has retreated. At the edge of the glacier there is ground-up rock called glacial till. Farther away is till covered with lichens. Back even farther, small shrubs and tree seedlings are growing. Where the glacier was long ago, there is now a mature forest.

When disturbances destroy an existing habitat, secondary succession may occur. This disturbance could be a forest fire or volcanic eruption. The plants and animals are gone, but the soil remains. Secondary succession begins on existing soil.

Pioneer species in secondary succession are small, fast growing plants that make many seeds. Next, taller plants and shrubs shade out, or grow around and above, the pioneers. Then, tree seedlings appear. Over time, a mature community returns. This process may take hundreds of years.

Succession can happen even in mature or climax communities. For example, when a tree falls in a mature forest, sunlight may again be able to reach the forest floor, which would allow new growth to begin. In this case, succession would begin with new smaller plants. Communities are always changing and growing.

Examples of ecological succession:

Example A - A dirt field is plowed and left over the summer. Over the summer, weeds start to grow on the field. After the weeds grow, small shrubs begin to take root. After a few years, trees begin to grow in the field.

Example B ? An old wheat field has been left alone by the farmer that once planted the field. After a while, grasses move into the field and begin to take over. Next, flowering plants, such as wildflowers begin to grow. Later, small shrubs begin to grow in the old wheat field. Finally, a few years later, native trees begin to grow in the field.

Example C - A sandy beach along the coast starts to have some small plants that have rapidly spreading roots. The plants take root and begin to grow. This brings in more fertile soil production and other shrubs begin to grow in the area. After a few years, trees begin to take root where there once was just a sandy beach.

Example D - A volcano erupted along a mountain side. After the eruption, the ground was basically just rock. Lichens and mosses began to grow on the rock and began to break down the rock to form soil. Small grasses begin to take root and start to grow also. Smaller shrubs come next. Small burrowing animals moved in to disturb the soil even more as larger plants start to grow. After several years, trees take root and grow where there once was only rock.

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