Control & Regulation

Control & Regulation Succession in Plant Communities Mr G Davidson

Plant Succession • If a field is abandoned and left bare, many seeds will land on it, but only some will survive. • This pioneer community will then be replaced by sturdier plants. • The organic matter of the pioneer plants will add to the soil fertility, providing better conditions for newer plants. G Davidson

Plant Succession • Eventually, this process will stop, usually with trees in this country. • These trees are known as the climax community. • The original colonisation of the bare field is known as primary succession. G Davidson

Plant Succession • The overtaking of a community by the next is known as secondary succession. • The plant occupying the field increases the favourability so much that it becomes more favourable to another community which soon takes over. • e.g. humus from dead leaves is broken down and makes the soil more fertile so that other, more demanding species can move in and choke out the existing community. G Davidson

Plant Succession • The Climax community is:- • the final product of succession • self-perpetuating • in dynamic equilibrium with its environment G Davidson

Plant Succession • As succession goes on, soil becomes deeper and organic matter and mineral contents rise. • The vegetation increases in size and biomass. • As a result of changing vegetation, supported animals also change. G Davidson

Plant Succession • The more developed the succession, the more diversity there is of life forms and the more complex the food-webs. • Soil type is affected by edaphic factors: • mineral matter • pH • humus content • These are affected by the climate and bedrock of a given area. G Davidson

Plant Succession • Some soils, however, are unable to support climax communities due to a lack of one of the above, for example: • The highest supportable community in this area is not known as the climax community, but as the edaphic climax community, which means that it is atypical of the climatic region in which it lives. G Davidson

Human intervention • In Britain, a few hundred years ago, the countryside was covered in the climax community of deciduous forest. • However, most of this has been cleared for settlement, conifer forestry and most importantly, agriculture. G Davidson

Human intervention • The constant use of the land prevents succession and stops climax communities from returning. • Further grazing by animals such as sheep also prevents saplings from developing into trees, and so the climax communities rarely develop. G Davidson

Control & Regulation