CBSE · Class 12 · Biology · EcosystemWhat is Ecological Succession? Differentiate between Primary and Secondary succession. Describe the process of succession on a bare rock (Xerosarch succession) in detail.

Definition of 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, and individual transitional communities are called seral stages.

Differences between Primary and Secondary Succession

1. Primary Succession:

   • Begins in areas where no living organisms ever existed, e.g., newly cooled lava, bare rock, newly created pond.
   • It is a very slow process, taking hundreds to thousands of years to reach a climax community.
   • Soil formation has to take place from scratch.

2. Secondary Succession:

   • Begins in areas where natural or human-induced destruction of a previously existing community has occurred, e.g., abandoned farm lands, burned or cut forests, flooded lands.
   • It is much faster because soil and some organic matter are already present.
   • Reaches a climax community relatively quickly.

Succession on a Bare Rock (Xerosarch Succession)

• Pioneer Species: Lichens are the pioneer species on a bare rock. They secrete acids to dissolve rock, helping in weathering and soil formation.
• Bryophytes: The small soil layer helps bryophytes (mosses) to grow, which hold more soil and organic matter.
• Herbaceous Stage: Higher plants like ferns, annual grasses, and eventually perennial herbs establish themselves.
• Shrub Stage: Woody shrubs and bushes replace the herbaceous plants due to accumulation of thicker soil layers.
• Climax Community: Finally, trees take over, leading to a stable and mature forest, which acts as the climax community.