Basic Types of Succession

Based on different criteria, there are following kinds of succession:

Primary succession
If an area in any of the basic environments (such as terrestrial, fresh-water or marine) is colonized by organism for the first time, the succession is called primary succession. Thus, primary succession begins on a sterile area (an area not occupied previously by a community), such as newly exposed rock or sand dune where the conditions of existence may not be favorable initially.

Secondary succession
If the area under colonization has been cleared by whatsoever agency (such as burning, grazing, clearing, felling of trees, sudden change in climate factors, etc.) of the previously plants, it is called secondary succession. Usually the rate of secondary succession is faster than that of primary succession because of better nutrient and other conditions in area previously under plant cover.

Autogenic succession
After the succession has begun, in most of the cases, it is the community it self which, as a result of its reactions with the environment, modifies its own environment and, thus, causing its own replacement by new communities. This course of succession is known as autogenic succession

Allogenic succession
In some cases replacement of one community by another is largely due to forces other than the effects of communities on the environment. This is called allogenic succession and it may occur in a highly disturbed or eroded area or in ponds where nutrients and pollutants enter from outside and modify the environment and in turn the communities.

Autotrophic succession
It is characterized by early and continued dominance of autotrophic organism such as green plants. It begins in a predominantly inorganic environments and the energy flow is maintained indefinitely. There is gradual increase in the organic matter content supported by energy flow.

Heterotrophic succession
It is characterized by early dominance of heterotrophic organism such as bacteria, actinomycetes, fungi and animals. It begins in a medium which is rich in organic matter such as small areas of rivers, streams; these are polluted heavily with sewage or in small pools receiving leaf litter in large quantities.

Induced succession
Activities such as overgrazing , frequent scraping , shifting cultivation or industrial pollution may cause deterioration of an ecosystem. Agricultural practices are retrogression of a stable state to a young state by man’s deliberate action.

Retrogressive succession
It means a return to simpler and less dense or even impoverished form of community from an advance or climax community. In most cases, the causes are allogenic, i.e forces from outside the ecosystem become severe and demanding. For example, most of our natural forest stands are regarding into shrubs, savanna or impoverished desert-like stands by the severity of grazing animals brought from surrounding villages. Excessive removal of wood, leaf and twig litter also leads to retrogressive succession.

Cyclic succession
It is of local occurrence within a large community. Here cyclic refers to repeated occurrence of certain stages of succession whenever there is an open condition created within a alarge community.

Ecological Succession

When stripped of it’s original vegetation by fire, flood, or glaciation, on area of bare ground does not remain devoid of plants and animals. Beginning with plants, area is rapidly colonized by a variety of both plant environmental factors. This modification of environment may in turn allow additional species to become established. The transitional series of communities which develop in a given area called sere or seral stages, while the final stable and mature community is called climax. The development of the community by action of vegetation on the environment leading to the establishment of new species is termed ecological succession. Succession is the universal proses of directional change in vegetation during ecological time. It can be recognized by the progressive change in the species composition of the community. Retrogression in community development does not occur unless succession is disturbed or halted by fire, grazing, scrapping or erosion.

Couses of Succession

Since succession involves a series of complex processes, so there exist many causes  of its occurrence. Ecologist have recognized the following three primary causes of succession:

1.       Initial or Initiating causes. There are climatic as well as biotic in nature. The climatic causes include factors such as erosion and deposits, wind, fire, etc., which are caused by lightening or volcanic activity. The biotic causes include various activities of organism. All these cause produce the bare areas or destroy the existing populations in an area.

2.       Ecesis or Continuing causes. These are processes as migration, ecesis, aggregation, competition, reaction, etc., which cause successive waves of populations as a result of changes, chiefly in the edaphic (soil) features of the area.

3.       Stabilising causes. These include factors such as climate of the area which result in the stabilization of the community.

 

Trends of Succession (Functional Changes)

Trends of changes during ecosystem development from a young to mature stage include the following features:

1.       A continuous change occurs in the kinds of plants and animals.

2.       An increase in the diversity of species takes place. The general appearance of the community or the physiognomy keeps on becoming more and more complex as succession proceeds.

3.       There is a progressive increase in the among of living biomass and dead organic matter. Such an increase occurs in gross as well as primary production in the initial and seral stages. Thus, there is more biomass accumulation, gradually reaching a huge biomass structure in the climax.

4.       Green pigment (chlorophyll) go on increase during the early phase of primary succession. The ratio of yellow/green pigments remains around 2 in the early stages and increases  to 3 to 5 in the climax stage. Pigment diversity also increases.

5.       The community respiration increases but the P/R (i.e. Production/Respiration) ratio remains more than 1 in the seral stages. The huge living biomass respires a lot in the climax stage and the P/R ratio equals 1 (i.e. PR 1). Thus, in the early stages P>R and in the climax stage P = R.

6.       The food chain relationships become more complex as succession proceeds.