Xerarch Succession:
Xerarch succession is a type of ecological succession that occurs in a dry environment, such as a desert or a rocky terrain. Pioneer communities that start the succession process are those that are adapted to extreme conditions such as high temperatures, strong winds, and lack of water. These pioneer communities are usually small and simple, often consisting of lichens, mosses, or algae.

Pioneer Community in Xerarch:
The pioneer community in xerarch is the first community that establishes in a dry environment. The pioneer community is the first stage in the process of xerarch succession. The pioneer community is established by organisms that are adapted to live in harsh conditions. The pioneer community is usually small and simple, consisting of lichens, mosses, or algae.

Lichen as a Pioneer Community:
Lichens are considered as a pioneer community in xerarch succession. Lichens are composite organisms that consist of a fungus and a photosynthetic partner, often an alga or a cyanobacterium. Lichens are adapted to survive in harsh environments, such as deserts, rocky terrains, and polar regions. Lichens are the first organisms to colonize bare rock or soil in a xerarch succession. They secrete acids that dissolve the rock surface, making nutrients available for other organisms. Lichens also trap dust and organic matter, creating a small amount of soil that allows other plants to grow.

Conclusion:
In xerarch succession, lichens are considered as a pioneer community. Lichens are adapted to survive in harsh environments and are the first organisms to colonize bare rock or soil. Lichens secrete acids that dissolve the rock surface, making nutrients available for other organisms. Lichens also trap dust and organic matter, creating a small amount of soil that allows other plants to grow.

Xerarch succession is a type of ecological succession that occurs on bare rock or soil that has no life. In xerarch succession, pioneer communities colonize the area and gradually change the environment, making it more suitable for other organisms to inhabit.

Among the options given, lichen is considered as a pioneer community in xerarch succession. Here are the reasons why:

What are lichens?
- Lichens are composite organisms that arise from algae or cyanobacteria living among filaments of multiple fungi in a symbiotic relationship.
- They can grow on rocks, soil, and bark of trees, where no other organisms can survive.

How do lichens initiate xerarch succession?
- Lichens secrete acids that dissolve the rock surface and release minerals, which contribute to the formation of soil.
- As lichens die and decompose, they add organic matter to the soil, further enhancing its fertility.
- Lichens also trap moisture and nutrients from the air, which helps to create a more hospitable environment for other organisms.

What happens after lichens?
- As lichens continue to grow and die, they create a thin layer of soil that can support the growth of other organisms, such as mosses and ferns.
- These plants further modify the environment, creating more soil, retaining moisture, and providing habitats for insects and other animals.
- Over time, the community of organisms becomes more complex and diverse, eventually leading to the establishment of a forest or other mature ecosystem.

Therefore, lichens are considered as a pioneer community in xerarch succession, as they are the first organisms to colonize the area and initiate the process of ecological succession.