Biol 4 Succession

Succession - the process by which an ecosystem changes over time. 

Primary Succession - where there was no established ecosystem before, there is no soil or organic matter. for example when a volcano erupts and forms a new rock surface which a plant species can colonise.

Secondary Succession - where there has been an established ecosystem that has been removed, but the soil remains. for example after a forest fire.

Primary Succession

• Starts when a species colonises a new land surface. 
• Seeds and spores blow in and grow.
• At first Abiotic conditions are harsh but the pioneer species are adapted to cope.
• They die and are decomposed (to humus) so create a basic soil.
• The conditions become less hostile, so new organisms can grow. 
• They die and further enrich the soil, making it deeper and containing more minerals.
• Larger plants can grow in the deeper soil and hold it together with its root structures. 
• The soil gets better and better, so more complex plants can grow, until the climax community is established.

Secondary Succession

• Happens quicker than primary succession because there is already soil in which larger plants can grow. 

At each stage for either primary or secondary succession, different plants and animals that are better adapted to the improved conditions move in, out compete the current species there, and become the dominant secies in the ecossytem. 

The ecosystem steadily becomes more complex, so new niches are created and the abundance of each species increases. 

The final Stage is called the Climax community, and remains this way as it is in a steady state. 

Different Ecosystems have different Climax communities. 

Which species make up the climx community is dependent on the climate. the climax community for a particular climax is called a climatic community. 

• In a temperate climate, there's a lot of water available, mild temperature and not much change between the seasons. The climatic climax will contain large trees because they can grow in these conditions once deep soil has been developed.
• In a polar climate, theres not much water available, temperatures are low, and there's huge changes between the seasons. Large trees cant grow in these conditions, so the climatic community is only likely to be herbs and shrubs.

Different Ecosystems have different Climax communities. 

Which species make up the climx community is dependent on the climate. the climax community for a particular climax is called a climatic community. 

• In a temperate climate, there's a lot of water available, mild temperature and not much change between the seasons. The climatic climax will contain large trees because they can grow in these conditions once deep soil has been developed.
• In a polar climate, theres not much water available, temperatures are low, and there's huge changes between the seasons. Large trees cant grow in these conditions, so the climatic community is only likely to be herbs and shrubs.

Managing Succession - Conservation

Human activities can prevent succession, to preserve a species or for aesthetic reaons. When succession has been stopped artificially like this it is called a plagioclimax.

• A regularly mown grassy field wont develop shrubs and woody plants, even if the climate of the ecosystem could support them. The growing points of the woody plants are cut off so they cant estalish themselves. Only the grasses can survive being mown, so the diversity stays low and succession cant progress.

Conservation sometimes involves preventing succession in order to preserve an ecosyatem in its current seral stage. For example, large areas of Scotland are kept as moorland to provide habitats for many of the plant and animal species. If the moorland was left to natural processes, succession would lead to the climax community of a spruce forest. This would mean the loss of the moorland habitat and could lead to the loss of some of the plants and animals that live there. Preventing succession keeps this habitat intact

• Animals are allowed to graze on the land - this is similar to mowing. The animals eat the growinf points of the shrubs and trees, which stops them establishing themselves and keeps the vegetation low.
• Managed fires are lit. After the fires, secondary succession occurs - the species that grows first, the heather, is the species that are trying to be conserved. The larger species take longer to gorw and will be removed the next time the moor's burnt.