Succesion

Over a period of time, the different species of organisms in a community are gradually replaced by others. This is succession. Think about the soil that accumulates at the base of a wall along the side of a concrete yard. It is colonised by small plants which are adapted to these conditions. These are known as pioneer species. If left undisturbed, many of these will die. Leaves and stems drop off and decompose, adding humus to the soil. Conditions will now be suitable for other species of plant which will gradually replace the original pioneers. If left undisturbed for long enough, a climax community is eventually established. In Britain, this is generally woodland of some sort. A climax community is the final stage in an ecological succession. 

Some terms used in describing succession

Pioneer community
The organisms that first colonise an area.

Climax community
The final stage in an ecological succession. The type of community formed depends to a large extent on the climate. In much of the south of Britain it is oak woodland; further north it is likely to be pine woodland. Climax communities are stable and change very little.

Sere
A sere is a complete succession from pioneer community to climax community, and a seral stage is a particular stage in this succession with its own distinctive community of organisms.

Primary succession
This is a succession in which the pioneer organisms colonise a surface such as bare rock or sand dunes on which nothing had been growing before.

Secondary succession
In contrast to primary succession, secondary succession is where pioneer species colonise an area where there has already been a community of living organisms but these have now been removed. Examples are the bare ground resulting from clearing forest or ploughing farmland.

 
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