(a) If both Assertion and Reason are correct and Reason is the correct explanation of Assertion.

Explanation:

Biotic or ecological succession is the formation of a series of biotic communities at the same site over a period of time one after the other, till a stable climax community develops over the area. It occurs generally in bare areas. Primary succession takes place on a biological sterile soilless primary barren area. Secondary succession takes place in a recently denuded area which still contains a lot of organic debris, remains and propagules of previous living organisms. The area has become bared due to destruction of the community previously present. The baring of an area can be caused due to forest fire, deforestation for wood, timber and habitat, overgrazing, landslides or earthquakes, excessive and repeated droughts, following a cropland and repeated floods.