Plant succession can be defined as the process of gradual replacement of one plant community by another plant community which is of stable type. It occurs over a period of time. The first plant community which develops in a bare area is known as pioneer community and the last invading community is called the climax community. The plant communities that develop during the succession are called the seral communities.
For e.g.:
Bare area or Substratum – Lichens – Bryophytes – Pteridophytes – Angiosperms (Climax Community)
There are two types of plant succession, as briefed below:
1) Primary Succession: It is the succession that starts from the primitive substratum, where there was no any sort of living matter previously.
For e.g.:
Bare area – Lichens (Pioneer community)

2) Secondary Succession: It is the type of succession which starts from previously built of succession, having already existing living matter.
For e.g.:
Lichens – Bryophytes – Pteridophytes – Angiosperms (Climax Community)

General Process of Succession:

The process of succession is accomplished through a series which includes the following steps:
1) Nudation: It is the development of bare area without any form of life. It may occur due to topographic reasons like landslide, flood, volcano etc and climatic glaciers, storm, dry period, fire, human activities etc.
2) Invasion: It is the establishment of a species in a bare area. This includes migration, establishment, aggregation i.e. the increment in the species number.
3) Competition and Coactions: Different species in a limited area compete for space, light, nutrition and so forth. Individuals of a species affect each other’s life in various ways which is termed as coactions.
4) Reaction: it is the modification of the environment through the influences of the living organisms (i.e. the condition of soil, light etc changes). It creates the favorable environment for a new species.
5) Stabilization: It is the final stage in which a community becomes sable for a longer period of time. Such community is termed as the climax community.

Concept on Climax Communities (Optional in this Question):
There basically are two types of theories on climax communities- monoclimax and polyclimax theories (for the explanations refer to books). Monoclimax theories suggests that the climax community is determined by climatic condition only whereas the poly climax theory suggests that except the climatic condition the climax community is determined by other multiple factors.

*Note: This was the greatly unexpected question (for 8 marks) in HSEB Exam 2069!!! Therefore, be prepared for such questions from each and every topic, and never ignore a single topic or question!!!