Plant Succession: Definition, Process, Causes & Types
Plant Succession Definition
They are born, develop and finally they become colonised by other groups of plants after maturity. This process of occupation of a particular area by different plant communities from their birth to maturity is known as plant succession.
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Plant communities are not stable in a particular area; instead, they are always changing from one type to another after their migration and occupation.
According to Clement, “Plant succession is the natural process by which the same locality becomes successively colonised by different groups or communities of plants.”
The occupation of an area from the beginning to the end i.e., climax or final stage is continuous and marked by a series of communities. these series of communities or in other words, intermediate stages (as seen between the beginning and the final stage) in the process of succession are called seral community or seral stages, which together or as a whole constitute a sere. The final steady state or stage in the succession is known as climax.
Primary Succession Definition
It has been noted that in most of the cases, succession begins on primitive substrata i.e., sterile area devoid of any vegetation. hence this type of succession is called primary succession.
Primary Succession Examples
A newly exposed sand dune or a recent lava flow.
Secondary Succession Definition
But when succession begins on areas previously occupied by well developed communities, or succession begins on areas where nutrients and conditions of existence of vegetation are already favourable, that type of succession is then called secondary succession or ‘sub-sere.’
Secondary Succession Examples
Abandoned croplands, plowed grasslands, cut-over forests, or new ponds
Succession may be autogenic or allogenic. In the former, the vegetation itself modifies the course of habit during succession. In the case of the allogenic type, some topographical conditions due to intense erosion or depositions are responsible for the course of succession.
According to Odum (1966, ’71), succession may be distinguished into two types e.g., (a) autotrophic succession and (b) heterotrophic succession.
The former is the common and wide-spread type in nature which begins in a predominantly inorganic environment and is characterised and dominated by autotrophic organisms.
Heterotrophic succession, characterised by heterotrophic organisms, occurs in special case where the environment is predominantly organic e.g., in a stream polluted with sewage or in a fallen log.
Depending upon the nature of habitats from which they originate, successions may be of several types. A sucession which had its origin in watery habitats (i.e. marshy grounds, ponds, lakes, or any other aquatic environment) is called Hydrosere. Similarly, a succession beginning in a dry area is known as Xerosere, in saline water Halosere and so on.
Succession is generally studied in two main types of habitats corresponding to the sere and the climax. the former is controlled by edaphic factors and the latter by climatic factors.
Sere is an open habitat and climax is closed type. In seral habitat, invasion and colonisation take place while in climax habitat, generally no fresh invasion takes place.
A. PROCESS OF PLANT SUCCESSION
In this process, migration of plants on a bare area from the neighbouring areas and aggregation on the spot of activity takes place. then the migrants react on the soil and adjust themselves to the local climatic conditions. Thus they become pioneer plants.
After getting acclimatised and balanced with the environmental conditions, pioneers begin to multiply. Subsequently interspecific and intraspecific competition for multiplying occurs.
As a result of this struggle for survival and supremacy, the number of plants decreases, – further decrease in the number of pioneers takes place as they react on the environment.
This changed environment becomes unsuitable for the growth and spread of the existing plants; as a result new channels open up for the incoming of new arrivals.
Pioneers, by their death and decay, increase the fertility of the soil which is suitable for the growth of new invaders. Thus community development progresses and number of new-comers at each stage decreases until the climax stage in reached when the entry of further new-comers is very difficult as the plants of the climax stage gain a good equilibrium with the environment to maintain and adjust their lives for long periods.
All types of successions, e.g., hydrosere, xerosere, halosere etc are characterised by a similar series of stages, viz.
(a) Nudation i.e., the formation of a bare area. (b) Migration and Colonisation. (c) Ecesis i.e., the establishment and final maturation of colonising species. (d) Aggregation
(e) Reaction between colonising species and habitat.
(f) Competition amongst the inter- and intraspecific plants – this is for the survival of the fittest.
(g) Stabilisation i.e., the attainment of stability of dominant species after competition, and
(h) Climax i.e., the final formation of species.
B. CAUSES OF PLANT SUCCESSION
In a habitat, the main cause of succession is climatic. It is the climate producing the bare area due to change in the climatic condition.
As a result, initiation of a sere begins. There are also some other agencies like destruction of vegetation by fire, land-slide, flood, etc. responsible for the starting of succession in vegetation.
When the vegetation of a primary succession is destroyed by anyone or all of the abovementioned factors, then secondary succession is set up. Sometimes, a succession after its development or initiation, may be deflected from its normal course by some disturbing factors like biotic agencies, fire, flood etc. Then it is called deflected succession.
Soil condition is another cause of shaping the nature of plant community – in a seral habitat, change from one type of community to another is largely dependent on soil condition.