Ecological Succession

  • An important characteristic of all communities is that their composition and structure constantly change in response to the changing environmental conditions.
  • This change is orderly and sequential, parallel with the changes in the physical environment.
  • These changes lead finally to a community that is in near equilibrium with the environment and that is called a climax community.
  • The gradual and fairly predictable change in the species composition of a given area is called ecological succession
  • The entire sequence of communities that successively change in a given area are called sere(s).The individual transitional communities are termed seral stages or seral communities. In the successive seral stages there is a change in the diversity of species of organisms, increase in the number of species and organisms as well as an increase in the total biomass.
  • Succession is hence a process that starts where no living organisms are there – these could be areas where no living organisms ever existed, say bare rock; or in areas that somehow, lost all the living organisms that existed there. The former is called primary succession, while the latter is termed secondary succession.
  • Examples of areas where primary succession occurs are newly cooled lava, bare rock, newly created pond or reservoir.
  • The species that invade a bare area are called pioneer species. In primary succession on rocks these are usually lichens which are able to secrete acids to dissolve rock, helping in weathering and soil formation. These later pave the way to some very small plants like bryophytes, which are able to take hold in the small amount of soil.
  • They are, with time, succeeded by bigger plants, and after several more stages, ultimately a stable climax forest community is formed.
  • Secondary succession begins in areas where natural biotic communities have been destroyed such as in abandoned farm lands, burned or cut forests, lands that have been flooded. Since some soil or sediment is present, succession is faster than primary succession
  • Based on the nature of the habitat – whether it is water (or very wet areas) or it is on very dry areas – succession of plants is called hydrarch or xerarch, respectively
  • Hydrarch succession takes place in wetter areas and the successional series progresses from hydric to the mesic conditions.
  • Xerarch succession takes place in dry areas and the series progress from xeric to mesic conditions

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