The process that changes the community, in an orderly or sequentially way, is called ecological succession. The succession leads to the formation of a stable community of organisms in a particular area after a certain period of time. The community that becomes stable after the successional changes is called “climax community”.
Hult first time used the term succession, in 1885. There are two kinds of succession, primary succession and secondary succession. When a community experience changes on an entirely new habitat, which has never been colonized before, then this is called primary succession while, the series of changes experienced by the community living on a pre-colonized area is called secondary succession.
Primary succession in open water like ponds, pools or lakes, which converted into land community, constitutes “hydrosere”. It is a plant succession which starts in the aquatic environment, called “hydrarch.” The changes taking place in the vegetation of hydrarch are called hydrosere. This kind of successional change is found in both animals and plants. However, it is more visible in plants. The seral stages in a pond are as follows:
i) Phytoplankton Stage: the colonial planktons are the first invaders of the pond. Algal spores brought by the wind, along with some soil particales, deposited in water. The phytoplanktons are the pioneer species, therefore, form the pioneer community. Phytoplankton includes blue-green algae (cyanobacteria), green algae ( spirogyra, oedogonium, ulothris, etc) bacteria, and diatoms.
ii) Submerged Stage:In this stage, soil become soft and suitable for the growth of rooted hydrophytes due to the decay of phytoplanktons and zooplanktons. Due to the decomposition of submerged organisms, soil become rich in nutrients and silting reduce the depth of water.
iii) Floating Stage:
Decaying of the hydrophytes of the submerged stage causes the decrease in the water depth few feet. Therefore, the plants, developed in this stage, are rooted in the soil and their leaves float on the surface of the water. These plants reduce water level by transpiration.
iv) Reed Swamp Stage:
It is also known as amphibious stage. In this stage, water table reduces and pond becomes shallower due to the decay of the plants and animals of the floating stage. The plants of this stage are slightly rooted in the soil and most of their parts are found above water table. These plants have walled-developed rhizome and thick vegetation.
v) Sedge Meadow Stage:
The soil, in this stage, becomes more suitable for plant growth due to the continues decomposing of the organisms of reed swamp stage and reduced water table. The plants of this stage have much branched rhizome system. The dense growth of plants also increases the rate of transpiration. The nutrients in the soil converted into oxides of nitrate and sulphates due to the action of oxygen.
vi) Woodland Stage:
Finally, woodland community of trees invades on the terrestrial environment. Now the vegetation of these trees is dependent on the environmental conditions.