Succession

Succession:

Primary Succession: starts in newly formed habitats, where there has never been acommunity before.

Secondary Succession: this is when one community changes into another. This is whenan existing community has been cleared, by something like a fire, and succession beginsagain.

The pioneer species: the first organism to begin to colonise the bear rock. Examplesof a pioneer species include lichen and algae. These are the only species that canwithstand the extreme temperature and lack of soil, water and nutrients.

The pioneer species begin to break down the rock, allowing some organic material toaccumlate. The organic material and small pieces of rock build up, and soil starts to form.

This change, along with a few other changes, allows for other species to begin to grow.One of these species would be the wind-blown moss spores.

Succession continues... the mosses will build up more organic material in the soil,which allows the soil to hold water. This means that small, shallow rooted plants are ableto take root, and establish themselves.

From here on conditions in the habitat improves and seeds from larger, taller plantsappear. They compete with the smaller plants that have already been established, andthey win. They replace the existing community.

Eventually... a community dominated (usually) by trees is formed. This is known as theclimax community, and is stable. This means it will remain unchanged until there is achange in the habitats conditions.

The climax community is dependent on environmental conditions (such as the soil typeand climate) and what species are available.

Secondary Succession:

When plants grow on bare soil, made by something like a forest fire, they mark the earlystages in secondary succession. This, if left, would lead to the re-establishment of thenatural forest climax community. In the UK this would be an oak forest, but in SouthAmerica this would be a rainforest.

Deflected Succession:

When a community remains stable because of human intervention, this is called deflectedsuccession. An example would be farm animals grazing preventing the grasslands fromturning into a woodland. Another example would be the community of organisms in yourgarden.

There are climax communities that are without trees, such as the Keen of Hamar. Theenvironment and underlying rock prevent much other then grass and a few rare plantsfrom growing. These are low-competition pioneer phase species, but have been theclimax community there for around 10,000 years.