(a) Succession of plants in a water body is called hydrarch succession.
(b)
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Hydrarch succession |
Xerarch succession |
Pioneer species |
It begins with phytoplanktons such as diatoms, green flagellates, single-celled colonial or filamentous green algae multiply rapidly and with their death and decomposition organic matter is produced. |
Crustose lichens (e.g., Rhizocarpus, Graphis, Lacanora, Rinodina, etc.) form the pioneer species in xerarch succession. As discussed, the lack of water prevents habitation but lichens can tolerate desiccation. Besides, they can also produce some organic acids that can cause rock weathering, thereby releasing the minerals essential for the growth of lichens |
Climax communities |
Forest stage represents the final stage of hydrarch succession and includes mixed forest vegetation. This is a climax community called climax forest. Several trees rapidly invade the woodland community of trees and shrubs. |
Forests are the climax community. The weathering of rocks and addition of more organic matter due to the death and decay of the plants makes the soil favorable for the growth of large trees. |
(c) The series of biotic communities that develop one after the other is called hydrosere. The various successional stages are:
(i) Plankton stage: It is the pioneer stage. This organic matter mixes up with clay and silt at the bottom of the water body to form soft mud favorable for growth of next seral stage.
(ii) Submerged stage: The soft mud supports the growth of submerged plants. They are rooted in the mud and from dense growth. Due to this sand and silt get deposited around the plants and therefore, bottom level rises slowly. The older plants and buried parts of other plants form humus on their death and decay. This enriches the newly built up bottom and makes it favorable for growth of next stage.
(iii) Floating stage: Floating leaved anchored plants appear when water becomes shallow and with their subterranean stems make the water rich in mineral and organic matter. As a result, water becomes suitable for growth of free-floating plants. These plants cover the water and their rapid growth further builds up bottom so that the water becomes shallow on the periphery.
(iv) Reed swamp stage: These are amphibious plants which grow where the water body becomes shallow. These plants transpire large quantity of water and produce abundant organic matter. Their tangled growth accumulates silt.
(v) Sedge or Marsh meadow stage: The plants invade the shores built up by reed swamp stage and transpire rapidly. They also add abundant humus, as a result of which soil is build up to invite next stage.
(vi) Scrub stage: The plants of this stage are rhizome bearing shrubs which can tolerate bright sunlight as well as water logged conditions. The shrubs invite invasion by trees capable of bearing bright sunlight and water logging. The plants of this stage lower the water table by their transpiration. They also built up more soil and shade loving plants start growing below them.
(vii) Climax forest: The climax forest depends upon the climate, for example, in moist tropical area rain forest is formed, in temperate area mixed coniferous forest or deciduous forest is formed.