An important characteristic of all communities is that composition and structure constantly change in response to the changing environmental conditions.
This change is orderly and sequential, parallel with the changes in the physical environment.
These changes lead finally to a community that is in near equilibrium with the environment and that is called a climax community.
The gradual and fairly predictable change in the species composition of a given area is called ecological succession.
During succession some species colonise an area and their populations become more numerous, whereas populations of other species decline and even disappear.
The entire sequence of communities that successively change in a given area are called sere(s).
The individual transitional communities are termed seral stages or seral communities.
In the successive seral stages there is a change in the diversity of species of organisms, increase in the number of species and organisms as well as an increase in the total biomass.
Succession can be of two types depending on the areas that are colonised:
- Primary succession: process that starts where no living organisms are there – these could be areas where no living organisms ever existed, say bare rock.
- Secondary succession: in areas that somehow, lost all the living organisms that existed there.

Primary succession:

Examples of areas where primary succession occurs are newly cooled lava, bare rock, newly created pond or reservoir.
The establishment of a new biotic community is generally slow.
Before a biotic community of diverse organisms can become established, there must be soil.
Depending mostly on the climate, it takes natural processes several hundred to several thousand years to produce fertile soil on bare rock.

Secondary succession:

Secondary succession begins in 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.

Succession of Plants

Based on the nature of the habitat – whether it is water (or very wet areas) or it is on very dry areas – succession of plants can be:
- Hydrarch succession takes place in wetter areas and the successive series progress from hydric to the mesic conditions.
- Xerarch succession takes place in dry areas and the series progress from xeric to mesic conditions.
Hence, both hydrarch and xerarch succession lead to medium water conditions (mesic) – neither too dry (xeric) nor too wet (hydric)

Hydrarch Succession:

In primary succession in water, the pioneers are the small phytoplanktons, they are replaced with time by free-floating angiosperms, then by rooted hydrophytes, sedges, grasses and finally the trees.
The climax would be a forest. With time the water body is converted into land.
Hence, it consists of following stages:
- Submerged stage: a number of submerged aquatic plants, such as Hydrilla, Elodea, Potamogeton, Ceratophyllum, Najas, Vallisneria, Utricularia, Ranunculus and several algae
- Floating stage: characterized by plants like Nymphaea, Polygonum, Limnanthemum and Castalia etc. These plants are rooted in the mud, and their broad leaves float on the surface of the water
- Reed-Swamp stage: by amphibious plants like Scirpus, Typha, Phragmites etc. These plants remain only partly submerged in water.
- Sedge meadow stage: characterized by plants like Carex, Juncus and Eleocharis.
- Woodland stage: dominated by shrubs and small trees
- Climax forest stage: large trees

Xerarch Succession:

In primary succession on rocks these are usually lichens which are able to 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 bigger plants, and after several more stages, ultimately a stable climax forest community is formed.
The climax community remains stable as long as the environment remains unchanged.
With time the xerophytic habitat gets converted into a mesophytic one.