`star` Types of Succession
`star` Xerarch Succession
`star` Hydrarch Succession


● An important characteristic of all communities is that `color{violet}"composition and structure"` constantly change in response to the `color{violet}"changing environmental conditions"`.

● This change is `color{violet}"orderly and sequential"`, `color{violet}"parallel"` with the changes in the physical environment.

● These changes lead finally to a `color{violet}"community"` that is in `color{violet}"near equilibrium"` with the environment and that is called a `color{brown}"climax community"`.

● The `color{violet}"gradual"` and `color{violet}"fairly predictable change"` in the species composition of a given area is called `color{brown}"ecological succession"`.

● During succession `color{violet}"some species colonise"` an area and their populations become more numerous, whereas populations of other `color{violet}"species decline"` and even `color{violet}"disappear"`.

● The `color{violet}"entire sequence"` of communities that `color{violet}"successively change"` in a given area are called `color{brown}"sere(s)"`.

● The `color{violet}"individual transitional communities"` are termed `color{brown}"seral stages"` or `color{brown}"seral communities"`.

● In the `color{violet}"successive seral stages"` there is a change in the `color{violet}"diversity of species"` of organisms, increase in the
number of species and organisms as well as an `color{violet}"increase in"` the `color{violet}"total biomass"`.

● The `color{violet}"present day communities"` in the world have come to be because of succession that has occurred over `color{violet}"millions of years"` since life started on earth.

● Actually `color{violet}"succession and evolution"` would have been `color{violet}"parallel processes"` at that time.

● `color{brown}"Succession"` is hence a process that starts where `color{violet}"no living organisms"` are there – these could be areas where no living organisms `color{violet}"ever existed"`, say bare rock; or in areas that somehow, `color{violet}"lost all"` the living organisms that
existed there.

● The `color{violet}"former"` is called `color{brown}"primary succession"`, while the `color{violet}"latter"` is termed `color{violet}"secondary succession"`.

● Examples of areas where `color{violet}"primary succession"` occurs are newly `color{violet}"cooled lava"`,`color{violet}" bare rock"`, `color{violet}"newly created pond"` or reservoir.

● The establishment of a `color{violet}"new biotic community"` is generally slow.

● `color{violet}"Before"` a biotic community of diverse organisms can `color{violet}"become established"`, there must be `color{violet}"soil"`.

● Depending mostly on the `color{violet}"climate,"` it takes `color{violet}"natural processes"` several `color{violet}"hundred to"` `color{violet}"several thousand"` years to produce fertile soil on bare rock.

● `color{brown}"Secondary succession"` begins in areas where `color{violet}"natural biotic communities"` have been `color{violet}"destroyed"` such as in abandoned farm lands, burned or cut forests, lands that have been flooded.

● Since some soil or `color{violet}"sediment is present"`, succession is `color{violet}"faster"` than primary succession.

● Description of `color{violet}"ecological succession"` usually focuses on `color{violet}"changes in vegetation"`.

● However, these `color{violet}"vegetational changes"` in turn affect `color{violet}"food and shelter"` for various types of animals.

● Thus, as `color{violet}"succession proceeds"`, the `color{violet}"numbers and types"` of animals and decomposers also change.

● At any time during `color{violet}"primary or secondary succession"`, natural or human induced disturbances (fire, deforestation, etc.), can convert a particular `color{violet}"seral stage"` of succession to an earlier stage.

● Also such disturbances create `color{violet}"new conditions"` that `color{violet}"encourage"` some species and `color{violet}"discourage"` or eliminate other species.


● Based on the nature of the habitat – whether it is `color{violet}"water"` (or very wet areas) or it is on very `color{violet}"dry areas"` – succession of plants is called `color{Brown}"hydrach or xerarch"`, respectively.

● `color{Brown}"Hydrarch"` succession takes place in `color{violet}"wetter areas"` and the successional series progress from `color{violet}"hydric to the mesic"` conditions.

● As against this, `color{Brown}"xerarch succession"` takes place in `color{violet}"dry areas"` and the series progress from `color{violet}"xeric to mesic"` conditions.

● Hence, both hydrarch and xerach successions lead to `color{violet}"medium water conditions"` (mesic) – `color{violet}"neither"` too dry
(`color{violet}"xeric"`) nor too wet (`color{violet}"hydric"`).

● The species that invade a `color{violet}"bare area"` are called `color{Brown}"pioneer species"`.

● In `color{violet}"primary succession"` on rocks these are usually `color{violet}"lichens"` which are able to `color{violet}"secrete acids"` to dissolve rock, helping in weathering and soil formation.

● These later pave way to some very small plants like bryophytes, which are able to take hold in the small amount of soil.

● They are, with time, succeeded by `color{violet}"bigger plants"`, and after several more stages, ultimately a stable `color{violet}"climax forest community"` is formed.

● The `color{violet}"climax community"` remains `color{violet}"stable"` as long as the environment remains unchanged.

● With time the `color{violet}"xerophytic habitat"` gets converted into a `color{violet}"mesophytic one"`.


● In `color{violet}"primary succession"` in water, the pioneers are the small `color{violet}"phytoplanktons"`, they are replaced with time by `color{violet}"free-floating angiosperms"`, then by `color{violet}"rooted hydrophytes"`, `color{violet}"sedges"`, `color{violet}"grasses"` and finally the trees.

● The `color{violet}"climax"` again would be a `color{violet}"forest"`.

● With time the `color{violet}"water body"` is converted into `color{violet}"land"`.

● In `color{violet}"secondary succession"` the species that invade depend on the `color{violet}"condition of the soil"`, availability of water, the environment as also the seeds or other propagules present.

● Since `color{violet}"soil"` is already there, the `color{violet}"rate of succession"` is much `color{violet}"faster"` and hence, climax is also reached more quickly.

● What is important to understand is that succession, particularly `color{violet}"primary succession"`, is a very `color{violet}"slow process"`, taking maybe `color{violet}"thousands of years"` for the climax to be reached.

● Another important fact is to understand that `color{violet}"all succession"` whether taking place in water or on land, proceeds to a `color{violet}"similar climax community"` – `color{Brown}"the mesic"`.