CBSE · Class 12 · Biology · EcosystemWhat is ecological succession? Explain the process of primary succession on bare rock (hydrarch or xerarch succession), detailing the various seral stages involved.

Introduction to Ecological Succession\nEcological succession is the gradual and predictable change in the species composition of a given area over a period of time. The entire sequence of communities that successively change in a given area is called sere. Individual transitional communities are termed seral stages or seral communities.

Xerarch Succession (Primary Succession on Bare Rock)\nWhen succession starts on a bare rock where no living organisms ever existed, it is known as primary succession. On bare rocks, it is specifically called xerarch succession because it starts in dry conditions. The various stages are:

1. Pioneer Species (Lichens):

   • Lichens are the pioneer species on bare rocks.
   • They secrete acids that dissolve rock, helping in weathering and soil formation.

2. Bryophytes (Mosses):

   • Small bryophytes follow lichens, establishing in the thin layer of soil formed by weathered rock and organic debris.
   • They build up a thicker mat of organic soil over time.

3. Herbaceous Stage:

   • As soil depth increases, larger plants like annual grasses and herbs manage to grow.
   • These replace mosses and further enrich the soil.

4. Shrub Stage:

   • Shrubs and woody bushes take over the area as soil continues to accumulate and hold more moisture.

5. Climax Community (Forest):

   • Finally, trees establish themselves, leading to a stable and mature forest community, which represents the climax community of that area.