Succession

A process by which communities of plants and animals colonise an area and then, over time, are replaced by other, more varied organisms.

Primary succession Starts from bare rock or water Primary succession is quite unusual in the world today. –Sand dunes are one of the few places where it takes place. –Volcanic island of Surtsey off Iceland

Stages in succession 1 Pioneer species These are the first species to colonise an area. They are able to withstand desiccation, extremes of temperature and low levels of nutrients

Stages in succession 2 The pioneer species penetrate and break up the rock. As the pioneer species die and decompose, humus builds up. Simple plants such as mosses and ferns can now grow.

Stages in succession 3 Mosses and ferns cast shade to stop further growth of lichens Their roots are longer and so further break up the rock. The organic matter gradually increases as these bigger plants die. More water is retained by this so grasses, small flowering plants and shrubs can grow.

Stages in succession 4 Growth of larger plants and the animals which inhabit them will cause further changes in soil and light conditions. The shading effect of the larger plants kills some of the smaller ones.

Stages in succession 5 Climax community Eventually the area is colonised by dominant plant species and a climax community is reached This would usually be oak woodland in the UK.

Primary succession - recap The plants present at each seral stage modify the environment making it more favourable for other plant species to colonise and out compete the current plants. e.g. the growth, death and decay of lichens produces organic matter which allows the growth of mosses which could not grow before the lichens

Primary succession - recap Bare rock Pioneers Grasses/herbaceous plants –often annuals Perennial herbs Shrubs/scrub Small trees Deciduous woodland – the climax community

Secondary succession This is much the same as primary succession except it occurs when the current seral stage is removed abruptly. This may be due to a natural disaster such as a fire or volcanic eruption, or by human influence such as deforestation and strip mining.

Secondary succession This time there is already soil and probably seeds present. This means the succession will happen more rapidly than primary succession. Wind blown plants that are tolerant to high levels of sun and grow fast called pioneer or fugitive species will colonise the area.

Deflected succession Often a climax community is not reached This may be due to human activity such as agriculture –e.g, chalk grasslands of the South Downs do not develop into woodland because of the grazing of sheep placed there by man.

Deflected succession Can also be the result of one or more limiting factors in the local environment –Woodland fails to develop around abandoned lead mines as many species cannot tolerate the high levels of lead in the soil Can also be called plagioclimax.

increasing time

increasing plant diversity

increasing animal diversity

increasing biomass

increasing complexity

increasing stability

increasing productivity

increasing height of plants

increasing n o of layers of vegetation

increasing n o of habitats

increasing n o of niches

increasing soil depth

increasing soil fertility

increasing soil organic matter

increasing soil water holding

simple food chains complex food webs

Surtsey- eruption

1967 colonization of lava flows by lichens/mosses

Higher plants