IBL - Succession Lesson

 

Succession

Interactions between life and the earth systems are constantly in motion changing the structure and composition of a community over time. When there is no change in a community it is considered to be stable and at equilibrium.  But sometimes there is a change to the ecosystem, whether it is natural or man made that disrupts this equilibrium. Sometimes an area can return to equilibrium and other times it cannot. Succession describes the sequential appearance and disappearance of a species in a community over time. There are two types of succession: primary and secondary.

Primary Succession

Primary succession occurs when new land is formed or rock is exposed. This will typically happen after a volcano erupts causing lava to flow. On the Big Island in Hawaii, 32 acres of land is added each year from the eruption of the volcanoes, so primary succession is constantly happening. First weathering and other natural forces break down the substrate enough for certain plants and lichen to start growing. These are known as pioneer species. These species help to break down the mineral rich lava into soil. Eventually less hardy plant species will grow and replace the pioneer species. As the early species grow and die, they add to the layer of organic material creating the soil. Over time the area will reach an equilibrium state.

Secondary Succession

In secondary succession, there is a disturbance such as fire, flood, hurricane, that disturbs the ecosystem but remnants of the previous community remain. A classic example of secondary succession occurs in oak and hickory forests (as seen in the picture) cleared by wildfires. The fires will burn most of the vegetation in an area returning their nutrients back to the ground in the form of ash.

The first plants back to the environment are usually annual plants, then grasses and pioneer species. Then, shrubs will emerge along with small pine, oak, and hickory trees. These organisms are called intermediate species. Over time, 125-175 years, the forest will once again reach equilibrium where species composition is no longer changing and resembles the community before the forest. This equilibrium state is referred to as the climax community, which will remain stable until the next disturbance.

 

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