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.