Question

Primary succession on rocks is known as xerosere. Answer the following related to xerosere.
a) Name the pioneer community.
b) Organic acids have important roles in this succession. Justify.

Answer 1

Succession is a process of directional change in community composition on an ecological time scale. It is of two types: Primary succession and Secondary succession. Succession that happens on land is called xerarch succession or xerosere region. Pioneer community is the first species that comes to exist on bare land.

Complete answer:
The succession is a process of change in a bare ecosystem based on an ecological time scale. The xerarch succession begins with the crustose lichen, which is also known as the pioneer species in primary succession. Primary succession is the most common type of succession. It includes the existence of some community or species on a bare land where no other community existed before. Succession can take place on land and water. The on-land succession is called xerarch succession. The region where xerarch succession occurs is called xerosere. It consists of a bare rock made of a solid surface because of which no prior roots were able to colonize. Species like Liconora , Rhinodina can adhere to the surface of the rock and absorb moisture from the air. The propagules of these lichens are brought from the surrounding areas. These are the symbiotic associations of algae and fungi. They have special arrangements called thalli. In thalli, they can collect wind-blown soil particles which help them to form a thin layer of soil. So, they are the pioneer community as they are the first to inhabit the bare rock surface to begin an ecosystem. These lichens produce acids that help in the corrosion of rocks. This leads to the formation of a thin layer of soil. Organic acids like oxalic acids also play an important role. This acid produced helps in causing crevices in rocks. In these crevices, organic matter submits. This causes the rocks to wither and form soil on which further succession can take place.

Note: The crustose lichen stage leads to the formation of the soil layer. Over this layer, the Foliose and Fruticose lichen stage succeeds. The shallow depressions are formed. The dead remain converted into humus. After this, the moss stage occurs. Certain changes occur in the environment that leads to the migration of lichens. This leads to the invasion of herbaceous plants. This further succeeds in the herb stage, shrub stage, tree stage, and then the forest stage.