Lithosere,First organisms,Moss stage,Grass stage,Shrub stage,Climax stage,Hydrosere,Dominance of species,Chemical and Physical

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Lithosere

Biotic succession occurring on bare rocks is called lithosere.

1. First organisms to establish on bare rocks are lichens which produce acids which corrode the rock surface. Timely addition of organic remains etc. brings about chemical and physical changes in structure of the substratum. Pioneer lichens are crustose lichens (Graphis, Rhizocarphon). Crustose lichens are replaced by foliose lichen (Parmelia) which cause greater erosion of the rock.

2. Moss stage.
Foliose lichen give way to hardy mosses (large sized, gregarious plant bodies which bear rhizoids to penetrate more into the rocks) which accumulate more soil and organic matter.

Lithosere Moss Stage

As a result substratum remains moist for a long time and finally weathering of rock starts. The spot now becomes ready for next invasion.

[Diagram shows general process of succession with different plant communities appearing therein under the influence of developing environmental complex, taking Hydrosere as an example. Note the pioneer, serial and climax communities.]

3. Grass stage.
During rainy season the mat of mosses formed over the fragmented rock becomes sufficiently moist wherein thereafter the seeds of grass germinate (Poa, Heteropogon, Dristida etc.). Their roots penetrate deeper in soil causing further fragmentation. More moisture and soil increases and sets stage for next succession.

4. Shrub stage.
No sooner seeds and rhizomes of xerophytic shrubs invade the area occupied by grasses (Zizyphus, Rhus, Rubus etc.) shrub penetrate deeper causing greater fragmentation.

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They shade the area, making it more moist inviting trees and other organisms.

Lithosere Shrub Stage

Diagram showing different plant communities appearing at different stages of Hydrosere originating in a pond.
[Note the gradual decrease in water level and successive development of the soil area to give finally a terrestrial habitat for forest climax community.]

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5. Climax stage.
Several hardy and light demanding trees grow in area occupied by shrubs. Slowly and gradually environment becomes more moist and shadier and the climax community spreads in the area.

Depending upon the type of nudity of area, succession is of two types: (a) Primary succession, (b) Secondary succession.

(a) Primary succession. Biotic succession which occurs on a previously sterile/primarily bare area. It is quite hostile to pioneer community. Some of the primary succession are newly exposed sea floor, igneous rocks, sand dunes, lava sediments or newly submerged areas. It takes al least 1000 years.

(b) Secondary succession. A succession that occurs on secondarily bared area due to destruction of community present previously. A secondary succession follows a climatic change-forest fire, major flood, overgrazed area, earthquake/landslide etc. Secondary succession is more quicker than primary succession as it grows on an already fertile soil. It takes 50-100 years (for grasslands) and 100-200 years (for forests).

Depending on the nature of substratum a sere is classified as:
(a) Lithosere = Succession on bare rock
(b) Prammosere = Succession on sand
(c) Hydrosere = Succession in water
(d) Xerosere = Succession in water-deficient area.

Hydrosere

Photoplankton stage (Diatoms, green flagellates)	®	Submerged stage (Hydrilla, Potamogeton, Najas)	®	Floating stage(Nelumbo Nymphaea)
				¯
				Reed swamp (Typha,saggittaria,phragmite
				¯
Climax forest (Oak, Elm, Fir)	¬	Woodland stage(Cornus, Popullus, Alnus)	¬	Marsh meadow stage(Caltha, Juncus Polygnum)

Dominance of species.
Succession stage reached in sere is named after the dominant the local environment are the most numerous in a succession.

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