Succession ,its types ,causes and theories

succession, causes of succession, types of succession and their process step by step ,Theories of succession

1. Succession Causes of succession Types of succession Theories of succession

2. Succession Succession may be defined as an orderly process of community change”. In the words of Salisbury , “ Plant succession is a competitive drift in which at each phase until the climax the constituent species render the habitat more favorable to their successors than to themselves.” Pioneer community : The first community to become establish in an area Climax community : The final community stage is called climax community

3. 2. Causes of Succession: The main causes of succession are as follows: Climatic causes Topographic causes Biotic causes

4. Climatic causes: plants cannot adjust with the long range variations in the climate. The fluctuating climate sometimes leads the vegetation towards total or partial destruction and, as a result, the bare area develops which becomes occupied by such plants as are better adapted for changed climatic conditions. The fluctuating climate sometimes leads the vegetation towards total or partial destruction and, as a result, the bare area develops which becomes occupied by such plants as are better adapted for changed climatic conditions.

5. Topographic causes These are concerned with the changes in the soil. Erosion of the soil: Sometimes surface soil is removed by a number of agents, such as wind, water currents, and rainfall. This process is known as soil erosion. In the process of erosion new and bare area is exposed in which new plant communities begin to appear one after another. Soil deposition: If the deposition of soil takes place over an area already covered with vegetation, the plants occurring over there may be suppressed and destroyed. Deposition results in a new bare area on which succession of vegetation starts.

6. Biotic causes: Many biological or living agencies also affect the vegetation in many respects. Grazing, cutting, clearing, cultivation, harvesting, and deforestation, all caused by living agencies, are directly responsible for vegetation change. The parasitic plants and animals also affect the vegetation and destroy it.

7. 3. Types of succession Plant succession may be of two kinds: Primary succession Secondary succession

8. Primary succession “Primary succession, type of ecological succession (the evolution of a biological community’s ecological structure) in which plants and animals first colonize a barren, lifeless habitat”

9. Primary succession

10. Secondary succession “ This kind of succession begins wherever the existing vegetation has been destroyed without denuding the area of soil.” It usually starts after forest fires, cutting of the trees, flood and erosions. It is also of common occurrence in abandoned agricultural lands.

11. Secondary succession

12. Sere and seral stages: A single case of plant succession at a particular kind of habitat is usually referred to as a sere, and the various stages of a sere are called seral stages. A single case of plant succession at a particular kind of habitat is usually referred to as a sere, and the various stages of a sere are called seral stages. Hydrosere: When succession starts in aquatic habitat Xerosere: When succession initiates on a dry, bare land. Lithosere It starts on a bare rock surface. Psammosere: Initiating on sandy habitats Senile It is the succession of micro-organisms and lower plants on dead plant parts and bodies. Eosere or Geosere It is the development of vegetation in an era.

13. 4. THEORIES OF SUCCESSION Monoclimax theory Polyelimax Theory Climax Pattern Theory

14. Monoclimax theory This theory was put forward by an American ecologist Frederick Clements in 1916. According to this theory there is only one climax community in a climatic or geographical region. But topographic differences and different soil types form other communities in the same zone. These communities are known as subordinate communities .the subordinate communities may be proclimax, post climax, disclimax, preclimax, and subclimax communities. Proclimax : The community which is more or less stable resembling the climax community is called proclimax. Disclimas: The community disturbed by man or other animals is called disclimax community. Its example is grassland in forest area. Subclimax or preclimax: The community in which development is stopped in the subtinal matte of succession due to burning, cutting or grazing and flooding is called subclimax or preclimax community. Post climax: The community in which a strip of vegetation of higher life form is found within a climax is called post climax community. Its example is forest strip along a stream in grassland.

15. Polyclimax Theory “this theory was put forward by European ecologists Nicholos. Champion and Whitaxer in 1953. According to this theory a number of different climax communities are present in climatic or geographical region. Thus preclimax, postelimax and disclimax communities are all climax communities. They are all self-reproducing communities. They can maintain themselves or an indefinite period of time. This theory does not rule out climax communities. But it gives other stages of communities as full status of climax communities. Thus these are not regarded as in minor communities

16. 3.Climax Pattern Theory This theory was put forward h Whitaker (1963). McIntosh (1958) and Sellech (1913). According to this theory the structure, composition and other characters of the climax communities are determined by the total environment of the ecosystem. It is not determined by single factor. Climax community is composed of an communities. These communities have close interrelationship the flora and fauna of the area soil and climate A particular plant cannot survive. Its seeds must be properly distributed. Similarly an animal cannot survive without food of plants. The climatic climax is the most popular community. The community which expresses the climate of the area is called cilmatric community.

17. 5. Stages of hydrosere and xerosere A ) stages of hydrosere

18. 1.Phytoplankton stage: They will be pioneer community Blue green algae , green algae, diatoms bacteria etc. They multiply and grow for some time Fix light energy Add nutrients to soil and water 2. Rooted submerged stage: Nutrients are added to the soil by the death and decomposition of planktons Soft muddy bottoms forms Bottom rich with silt Water depth becomes shallower Light penetration become easy This promote the growth of rooted hydrophytes Example: Hydrilla,Vallisneria,utricullaria

19. 3.Rooted floating stage : More reduction in water depth Increase in the width of bottom soil/silt Death and decomposition of rooted plants and nutrients Rooted floating plants starts to appear Example :Nelumbo, Nymphea, Trapa Free floating plants can also develops :Azolla, Lemna, Wolffia, Pistia, Salvinia 4 .Reed-swamp stage: Also called amphibious stage Water level very much reduced Soil and silt level increases Soil become more fertile by death and decay of plants Most of the plant will be rooted, but their shoots exposed to air Have well develop rhizome Forms very dense vegetation Example :Typha, sagitaria

20. 5. Sedge Meadow Stage Water level further decreases Soil level further increases Plants of cyoeraceae and poaceae predominate They forms mat like vegetation over the top of the soil Rhizome well developed and interconnected Have high rate of transpiration, water level further reduced Soil exposed to air Nutrients like ammonia and sulfides become oxidized to nitrates & sulfates Terrestrial soil formation proceeds Woodland stage: Soil become drier most of the times Marshy vegetation replaced terrestrial plants Shrubs and herbs predominates Small trees also occurs Huge accumulation of humus occurs Variety of decomposers in the soil Fertility of soil increases Example of plants : Salix ,Eupatorium ,Alnus

21. 7. Forest stage Climax community Wood land community is invaded by tree forms Tree forms predominate Canopy cover the entire area Light penetration to the lower canopy reduced Herbs and shrubs highly reduced Wooded climbers also predominates Climate determines the type of forest (evergreen ,deciduous etc.) Example of plants: Shorea, Quercus,Acer

22. Stages of hydrosere

23. Stages of xerosere 1. bare rocks The first form of life originate 2.Crustose lichen : Lichen is important pioneer in primary succession composed of phosynthesizing algae and fungi absorbing nutrient from rocks They break down rocks Soil accumulate as particles trapped in cracks of ricks Lichen decompose provide food for mosses

24. Foliose of lichen stage The can be absorb more water and able to accumulate more soil particle The shallow depression in rocks filled with sold and topsoil further increase These autogenic changes favor growth and establishment of mosses Mosses stage Mosses develop in patches they catch soil particles from air and increase the amount of substratum The changing environment leads to migration of lichen and help in invasion of herbaceous vegetation that out compete mosses

25. Herb stage: Herbaceous weeds such as milk weed and evening primroses invade the rocks Their root penetrate deep secrete acid and enhance weathering Leaf liter and the death of herbs add humus to the soil Shrub stage The herb and grass mixture is invaded by shrub species, such as Rhus and Phytocarpus. Early invasion of shrub is slow, but once a few bushes have become established, birds invade the area and help disperse scrub seeds. Climax stage : The succession culminates in a climax community, the forest. Many intermediate tree stages develop prior to establishment of a climax community.

26. Stages of xerosere