Succession Succession Ecosystems are constantly changing Succession describes

Succession

Succession • Ecosystems are constantly changing. • Succession describes the changes in species and physical environment in an area over time. • takes place in a series of stages (seres). At each stage, certain species colonise and change the environment so that it becomes more suitable for others

How Does Succession Work? There are 2 types of succession: PRIMARYPlants grow where NO PLANTS HAVE GROWN BEFORE. SECONDARYPlants grow where there has been a previous population. These will have been destroyed, eg: by fire

Primary succession • Starts from (newly formed)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

Difficult to live on a rock surface. Why? • Too exposed. • No soil. • Temperatures fluctuate. • Dry. • No easily available nutrients.

How does succession work? A bare patch of ground will not stay bare. It will rapidly be colonized by a variety of plants. A recently cleared patch of ground The same ground 2 years later

The 1 st species to colonise are called PIONEER SPECIES. The “ultimate” species to colonise are called the CLIMAX COMMUNITY. Sand dune succession. The pioneer species is marram grass.

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

Pioneer species • are often 'opportunist' species which are able to rapidly exploit a sudden new opening in ground plant cover. (no dormancy period) • They must be able to grow quickly. They are usually short-lived. EXAMPLE: Mosses • They are low growing • They then provide a microhabitat equivalent to a miniature forest for a variety of invertebrates such as mites and spiders. • The moss also acts like a sponge when wet, in some cases providing a semi-aquatic microhabitat

Stage 2 • 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.

Stage 3 • Growth of larger plants such as shrubs 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.

Stage 4 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 – main principle • The plants present at each seral stage modify the environment • These changes makes conditions 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 – E. g Clover, moss • Grasses/herbaceous plants –often annuals. – E. g foxglove • Shrubs/scrub – E. g. Bramble, hawthorn • Small trees – E. g. birch • Deciduous woodland – the climax community – E. g Oak

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 and animal diversity Biomass Productivity Complexity Stability

increasing number of layers of vegetation + plant height Numbers of habitats Number of niches Complexity of food webs

increasing soil depth soil fertility soil humus (organic matter) Mt St Helens Water retention

Surtsey- eruption 1963 -67

1967 colonization of lava flows by lichens/mosses

Higher plants