Ecological sucession,SUCESSION,HYDROXERE

Ecological sucssion,SUCESSION,HYDROXERE,ECOLOGY,ENVIORNMENT,

1. ECOLOGICAL SUCCESSION Submitted To- Dr. Ashun Submitted By – UDAYPAL Roll. No. – CUHP20PLS30 MSc . Plant Science

2. ECOLOGICAL SUCCESSION Ecological succession is a gradual and orderly process of change in an ecosystem brought about by the progressive replacement of one community by another until a stable climax is establish. Each succession begins by a few hardy invaders called pioneers. Succession ends with a diverse and relatively stable climax community. The entire sequence of communities that successively change in a given area is called sere. The individual transitional communities are termed as seral stages or seral communities .

3. Characteristics of Ecological Succession Succession has the following characteristics: 1. It is a systematic process which involves change in species structure. 2. The changes are directional and take place as a function of time. 3. The succession occurs due to the changes in physical environment and population of species. 4. The changes are predictable and the process of succession is self going.

4. Types of Succession Xerach Succession : The succession initiated in extremely dry situations such as bare land , sand, etc. The different stages in this succession are called Xerosere. It can be subdivided ; Lithosere (Xerosere which originates on rock surface) and Psamosere (xerosere which origin on sand). Hydrach Succession : The term refers to succession beginning in water, or in pond, lake, marshes, etc. The various stages of this succession are called Hydrosere . The succession occurs on saline water is called halosere whereas the succession that occurs on acidic bog is called oxylosere .

5. Primary Succession : It is an ecological succession of plant life occurring on sites which have previously no living organisms (these could be areas where no living organisms ever existed vegetation) . The areas where the primary succession takes place are bare rock , cooled lava, newly created pond or sand or clear glacial . The establishment of a new biotic community is generally slow . There must be soil before establishment of a biotic community of diverse organisms. The formation of soil depends mostly on the climate and it takes several hundred to several thousand years to produce fertile soil on bare rock. Secondary Succession : It is the series of community changes that take place on an area that somehow, lost all the living organisms that existed there. Secondary succession begins in the areas where natural biotic communities have been destroyed such as in abandoned farm lands burned or cut forests, lands that have been flooded. Since some soil or sediment is present, succession is faster than primary succession.

6. Autotrophic Succession : It is characterized by early and continued dominance of autotrophic organisms like green plants. It begins in a predominantly inorganic environment. Heterotrophic Succession : It is also known as micro-succession. This involves the succession of micro organisms. It begins in predominantly organic environment and there is a progressive decline in the energy content.

7. Autogenic Succession : The succession in which organisms themselves bring change in the environment during succession is called autogenic succession. For example, larger species like trees produce shade on to the developing forest floor. It destroys the light-requiring species, whereas the shade-tolerant species in the area get established. Allogenic Succession : The succession in which external environmental factors cause change in the environment during succession is called allogenic succession. Soil erosion, leaching or the deposition of silt can change the soil. Animals also play an important role in the allogenic changes. They act as pollinators, seed dispersers . They can also increase the nutrient content of the soil in certain areas.

8. Retrogressive Succession : It is defined as the reversion to some earlier stage of succession consequent on the introduction of an adverse factor-like excessive population of herbivores , overgrazing by cattle, felling of tree etc. Induced Succession : The climax community has low productivity as compared to the initial communities. The respiration almost balances the production of organic matter in climax community. Hence, a very little is left for men to harvest. Man has controlled succession to obtain a managed steady state to get maximum amount of organic matter. It is known as induced succession, e.g. agriculture.

9. General Process Of Ecological Succession : Nudation : It is the creation of bare area without any life form. This formation can be due to landslide, volcanic eruption and soil erosion (topographic factor), or due to drought, hail, and fire (climatic factor) or due to overgrazing, cutting of trees, industry, agriculture, housing a disease outbreak, etc. (biological factor). These all factors cause destruction of existing vegetation and make an area bare of vegetation. Invasion : This is the successful establishment of a species in a bare area. The species in arrive at this new site from any other area. This whole process is completed in the following succession stage: Migration : It starts with migration where some seeds, spores from the nearby localised reach the bare area through air, water etc. in the form of propagules. Propagules are a vegetative structure. Migration is controlled by four factors - agent, distance, mobility and topography. The first arrival in the bare area is known a pioneer and the occupation of bare area by these pioneers is called colonization

10. Ecesis : After migration, successful establishment of the species is known as ecesis . It is no necessary that all the migrated propagules must stabilize. The stabilization process depends great on the conditions prevailing in that area, and only those species establish which adjust with the existing condition. Aggregation ; Number of species increases due to reproduction and they come to close each other. It may be simple (increase numbers of pioneer only) or mixed (increase in numbers of pioneer and other invaders).

11. Invasion : New species continue to reach the area after the establishment of the pioneer. These new species also establish in new area and the process is known as invasion and the species a known as invader. Only those invaders establish which adjust with the existing condition. Competition : After aggregation of a large number of individuals of the different species at the limited place, there develops a competition. The competition develop among the individuals of different species (interspecific) or among the individuals of the same species (intraspecific). The competition occurs for space, food, light, minerals and water . Intraspecific is an in competition is more severe because these individuals require same kind of habitat and nutrition.

12. Reaction: This is the most important stage in succession and it includes method of the modification of the environment through the influence of living organism on it. Once the number of different species increases, they have a strong influence on the physical environment and the mechanism of the modification the environment through the influence of living organism on it, known as reaction. Most of the changes occur in soil, water, temperature and light conditions etc. Due to all these reaction, the environment is modified, (becoming unsuitable for the existing community which is replaced by another seral community. The whole process of replacement of one community by other community in the given area in a definite sequence is known as a sere, and various communities constituting the sere as seral communities. Stabilization (Climax): This is the final stage of development and known as climax community. Climax community is nearly stable and will not change so long as the climate and physiographic factors remain the same.

13. Hydrosere This type of succession starts in a water bodies like pond and ends in a climax community as a forest. As succession continues in such areas, the environment gradually becomes drier. The hydrosere succession is primary succession .

14. There are seven stages in the Hydrosere Succession : Phytoplankton Stage : The phytoplankton ( phyto -plant, plankton-floating) are the pioneer community in hydrosere . Unicellular floating algae such as diatoms, blue green algae and bacteria are pioneer species in a water body. The phytoplanktons are followed by zooplanktons. They settle down to the bottom of the water body after their death and decay and add organic matter and nutrients. The organic matter mixes with the silt and forms a soft mud at the bottom. As soil builds up, the pond becomes shallower and favours the growth of the next seral stage.

15. Submerged Stage : Some rooted submerged (under the surface) species become established as the water body becomes shallower. The submerged aquatic vegetation grows in the regions of ponds and lakes where the water depth is about 10 feet or more and light can penetrate up to the bottom. Once submerged species colonize, the successional changes become more rapid as organic matter accumulates at the bottom. Consequently, the pond or lake becomes sufficiently shallow (2-5 ft) due to more humus formation because of the death and decay of older and buried parts of the submerged plants. This changed habitat becomes less suitable for the rooted submerged plants but becomes more suitable for the growth of floating species.

16. Floating Stage : The floating species become established in shallow waters of water bodies. The floating species are rooted in the mud, but some or all of their leaves float on the surface of the water. The floating hydrophytes Azolla, Lemna , Pistia , Salvinia and Wolffia . The large and broad leaves of the floating plants shade the water surface and conditions become unsuitable for growth of submerged species. The plants decay to form organic mud which makes the pond shallow. This modified environment becomes suitable for the establishment of reed swamp stage.

17. . Reed Swamp Stage : This stage is also known as the amphibious stage . When the water depth is 1 to 3 feet. the pond is invaded by plants that are rooted with most of their shoots exposed to the air. Important plant species of this stage are Phragmites (reed-grasses), Typha (cattail), and Sagittaria . The foliage leaves of such plants are exposed above the surface of water and roots are generally either anchored in mud or submerged in water.

18. The foliage leaves form a cover over the submerged and the floating plants which devoid them changes of light. Neither the submerged nor the floating plants can survive under such conditions of Transpiration, deposition of soil and plant debris at the bottom of water bodies reduce the depth of water and make the habitat less suitable for the pre-existing plant species. The secondary species such as Polygonum , Sagittaria , etc. start appearing. Later, these plants also bring about some which make the habitat more suitable for the next stage of plants.

19. Sedge Meadow Stage : The successive decrease in water level finally results in a marshy so which may be too dry for the plants of pre-existing communities. Now, the plants well adapted to new habitat begin to appear in the pre-existing community in a mixed state. The members of Cyperaceae and Graminae families are well suited to the marshy habitat. The prominent species of this stage are sedges (members of the Cyperaceae like Cyperus, Carex , Juncus, etc.), Mentha, etc. As these plants grow in the marshes, they modify the habitats in numerous ways. They absorb and transpire large quantity of water and also add to the accumulating soil at the base. This results in a dry habitat, totally unfit for the growth of normal hydrophytes. Gradually, the mesophytes start appearing, which replace the sedge vegetation later on.

20. Woodland Stage ; The soil gets dry in due course of time and becomes suitable for development of wet woodland species. It is invaded by Shrubs in the beginning but medium size trees also appear in the later stages. These plants provide more shade and absorb & transpire large quantity of water. Thus, they make the habitat drier. Shade loving herbs may also grow under the trees and shrubs. The important plants of woodland community are species of Alnus, Acacia , Cassia, Terminalia, etc. The changed habitat becomes suitable for the growth of final climax stage.

21. Forest Stage : The woodland stage may lead to the development climax vegetation in the last stage. The habitat becomes drier and well aerated due to the raised level of above the water level by progressive accumulation of humus and soil particles. The stable uniform plant community consisting mostly of woody trees (i.e. all trees, shrubs ).

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