Hydroseres : Definition, development stages

Hydroseres : Definition, development stages

The succession is found in water is called hydrarch and various stages of the succession are called hydrosere.

It is a series of developmental stages that occur during succession in a body of water (lake, pool or pond). Succession is quite conspicuous in standing water of moderate depth. It is slow and inconspicuous in a water mass having great depth or strong wave developmental stages of a hydrosere are as follows -

1. Phytoplankton stage - The Phytoplankton stage is the initial stage of hydrosere. (Example- diatoms, various species of green algae, blue green algae. bacteria, etc.) All the available resources needed for their growth and multiplication. They have the ability to fix atmospheric nitrogen and multiply them rapidly. Their dead organic remains go on depositing in mud and release nutrients through decomposition.
2. Rooted submerged stage - Dead organic remains of phytoplanktons develop a thin layer of soft mud at bottom which favours submerged hydrophytes like Hydrilla, Ceratophyllum, Najas, Vallisneria, Potamogeton, Utricularia or Myriophyllum. These plants have potentiality of producing large amount of soft muds by donating their dead organic remains. They grow faster and gradually occupy the bottom area where light is available for their photosynthesis.
3. Floating stage - When the thickness of soft mud at the bottom increases beyond 4 to 6 inches, floating leaved hydrophytes like Nelumbo, Nymphaea, Nymphoides, Eurale or Victoria invade the pond. They have rhizomatous habit or produce tubers which remain burned in the soft mud and produce floating leaves with long petioles to float over the surface of water. Free-floating stage Plants floating freely over the surface of water invade the pond after rooted floating leaved stage. Eichhornia, Lemna, Spirodela, Wolffia, Pistia, Azolla or Salvinea dominate in this stage of succession. They further eliminate the submerged communities by preventing entry of sun light into water.
4. Reed swamp stage (Amphibious stage) - In this stage, attached emergents like Scirpus, Typha, Sagittaria, Monochoria, Eleocharis etc. predominate and form largely having creeping rhizomes burned in mud and abundance of nutrients releasing from rapid decomposition of dead organic remains of previous occupants. The pond gradually converts into a swamp and presents an unfavourable environment for true hydrophytes.
5. Sedge meadow stage - Like Cyperus, Vitiveria, Juncus, Ranunculus, Dentella, Limnophila, etc., now start replacing the Reed swamp vegetation gradually and they develop terrestrial look to the pond. They have the capacity of enjoying aquatic as well as terrestrial environments and they will continue their growth till the shrubs and trees start invading the area. The soil becomes almost dry but possesses high level of fertility.
6. Woodland stage - Shrubs and trees start appearing at this stage by gradually replacing Sedge meadow stage. Example- Salix, Populus, Almus, Terminalia, Eugenia, etc., predominate at this stage and the trace of a pond has altogether disappeared. This is the beginning of climax of the succession.
7. Climax community - In hydrosere, the climax is attained when the forest develops at this area predominated by trees with a few shrubs and ground flora. Forest represents a most stable community capable of maintaining a dynamic equilibrium with the prevailing environmental conditions. Nature of forest and its vegetation composition depend upon the climatic and geographical conditions of the area. Deciduous trees predominate under the tropical environment (Shorea, Tectona, Eugenia, Terminalia, Bauhenia, Mallotus, Barrigtonia, Delbergia, Acacia, etc.), whereas, the evergreens under temperate environment (Pines, Cedrus, Junipers, etc.).