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Succession

Succession describes the changes in species and physical environment in an area over time. There are two types: primary succession (no previous plants) and secondary succession (after previous population). This process occurs in stages, with pioneer species colonizing first and climax communities forming later.

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Succession

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  1. Succession

  2. 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

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

  4. 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

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

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

  7. The 1st 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.

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

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. 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

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. increasing time

  20. increasing Plant and animal diversity Biomass Productivity Complexity Stability

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

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

  23. Surtsey- eruption 1963-67

  24. 1967 colonization of lava flows by lichens/mosses

  25. Higher plants

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