Hydrosere (Hydrarch Succession) with PPT

What is Hydrosere or Hydrarch Succession?

A succession originates in a water body (aquatic environment) is called Hydrosere or Hydrarch Succession. Such a succession does not necessarily lead to the development of a land community. If the water body is sufficiently large and with wave action, the succession usually results in the formation of a large aquatic climax community.

If the hydrarch succession starts from a comparatively small water body such as a pond, there is always a high probability for the formation of a terrestrial climax community. The important characteristics of hydrosere are given below:

Learn more: Process of Ecological Succession

Learn more: Types of Ecological Succession

Ø  Hydrosere usually starts from a pond

Ø  Phytoplanktons will be the pioneer community

Ø  A forest or a grassland will be the climax community

Ø  Includes several seral stages of plant and animal communities

Ø  Seral communities of plants are more obvious than animals.

Just like other successions, the hydrosere is also completed through a sequence of several Seral Stages (Seral Communities). The seral stages of a typical Hydrosere succession are as follows:

Seral stages of Hydrosere

(1).  Phyto-planktons stage

(2).  Rooted submerged stage

(3).  Rooted floating stage

(4).  Reed-swamp stage

(5).  Sedge-meadow stage

(6).  Woodland stage

(7).  Forest stage

(1). Phytoplankton stage:

Ø  Phytoplanktons will be pioneer community in the hydrosere.

Ø  Algal spores are brought into the water in the initial stages of the succession.

Ø  These algal spores germinate and quickly colonize in the water body.

Ø  They multiply and grow for some time. They fix light energy (photosynthesis).

Ø   Blue green algae, green algae, diatoms, bacteria etc. the plankton communities.

Ø  Large number of minute free floating zoo-planktons will also appear.

Ø  Various growth activities of these planktons and their death add nutrients to soil and water.

Ø  After their death, they settle down at the bottom of the pond to form a layer of muck.

(2). Rooted submerged stage:

Ø  Nutrients are added to the soil and water by the death and decomposition of planktons.

Ø  Subsequently a soft muddy bottom with rich silt forms.

Ø  Due to the formation of muddy bottom, the water depth becomes shallower.

Ø  Once the water depth is reduced to about 10 feet, the complete light penetration becomes easy.

Ø  This promotes the growth of rooted submerged hydrophytes.

Ø  These plants will be completely submerged in the water.

Ø  Example: Hydrilla, Vallisneria, Utricullaria, Chara, Ceratophyllum

Ø  The nutrient rich muddy bottom helps to quickly flourish their population.

(3). Rooted floating stage:

Ø  When the depth of water reaches about 4 to 8 feet, the submerged vegetation starts disappearing from their original place.

Ø  Death and decomposition of these rooted plants add more nutrients to the soil.

Ø  This further increase the width of bottom soil or silt.

Ø  In this condition, rooted floating hydrophytes starts to appear.

Ø  These rooted floating plants quickly cover the water surface and their floating leaves completely cover the water body.

Ø  As a result of this, the light penetration into the water is inhibited and this results in the complete disappearance of submerged plants.

Ø  Examples of rooted floating plants: Nelumbium, Nymphaea, Trapa

Ø  Free floating plants can also develop: Azolla, Lemna, Wolffia, Pistia, Salvinia

(4). Reed-swamp stage:

Ø  The Reed-swamp stage is also called the Amphibious Stage.

Ø  The water level very much reduced (reduced to 1 to 3 feet).

Ø  The level of soil and silt increases and in this condition, the rooted floating plants cannot survive there.

Ø  The soil becomes more fertile by death and decay of plants.

Ø  In this stage, the rooted floating plants are replaced by plant communities which can survive both in water and terrestrial conditions (hence the name amphibious stage) will develop.

Ø  Most of these plants will be rooted, but their shoots are exposed to the air. They have well-developed rhizome.

Ø  Plants in this stage form very dense vegetation over the area and this will prevent the light penetration to the lower portion.

Ø  At this condition, the remaining rooted floating or free floating or submerged plants of the previous seral stage disappears.

Ø  Example: Typha, Sagittaria, Polygonum

(5). Sedge Marsh or Meadow Stage:

Ø  Water level further decreases and the filling process results in the formation of a marshy soil.

Ø  The marshy soil is unsuitable for the pre-existing community (reed-swamp community).

Ø  Plants of Cyperaceae and Poaceae start to develop and they predominate in the area.

Ø  The rhizomes of these plants are well developed and they are interconnected to each other.

Ø  They form mat-like vegetation over the top of the soil.

Ø  The luxurious growth of these plants will modify the current soil.

Ø  These plants have a high rate of transpiration and they remove a large amount of water from the soil results in further reduction of moisture.

Ø  Due to loss of water by transpiration, the soil becomes exposed to air for the first time.

Ø  Once the soil is exposed to the air, the nutrients such as ammonia and sulfides become oxidized to nitrates & sulfates. Oxidation also results in the breakdown of other complex organic components in the soil to simple compounds.

Ø  All these ultimately results in the formation of Terrestrial Soil.

(6). Woodland stage:

Ø  In this stage, some shrubs and medium sized trees will starts to appear.

Ø  These plants will prevent the light penetration to the bottom region and hence the marshy vegetation in the body gradually shrinks.

Ø  The soil will stay dry in most of the time.

Ø  Shrubs and herbs gradually predominates the area.

Ø  Shedding of leaves from the shrubs and trees results in the huge accumulation of humus in the soil.

Ø  A variety of decomposers of bacterial and fungal groups in the soil quickly break-down these organic matter results in a further increase of fertility of the top soil.

Ø  Example of plants: Salix, Eupatorium, Alnus,Acacia, Cassia, Terminalia

(7). Forest stage:

Ø  Forest stage is the climax community in hydrarch succession.

Ø  The woodland community is invaded by large tree forms.

Ø  Tree forms gradually predominate the area and their canopy covers the entire area.

Ø  The light penetration to the lower canopy becomes reduced and this results in the reduction of herb and shrub population.

Ø  This condition also promoted the occurrence of large wooded climbers. These climbers (lianas) will climb over the trees for sunlight.

Ø  The climate of the region determines the type of forest (evergreen, deciduous etc.)

Ø  Example of plants: Shorea, Quercus, Acer

The climax forest community is stable and self-sustainable. All types of communities such as herbs, shrubs, trees, climbers, animals, decomposers etc. are present in the climax community in correct proportion. At the climax stage, a complete harmony is developed between the plant communities with the habitat. The process of hydrosere is a gradual process and it may take thousands of years to complete.

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