Why are lichens and moss called the pioneer species in communities established on bare rock?

Lichens and moss are called pioneer species in communities established on bare rock due to their role in primary succession, a process where life begins to return to an ecosystem that was previously disrupted or damaged. Here are the steps explaining why:

1. Survival in harsh conditions: Lichens and mosses are among the few organisms that can survive in the harsh conditions of bare rock. They can withstand extreme temperatures, low nutrient availability, and high light intensity.

2. Physical weathering: Lichens and mosses contribute to the physical weathering of the rock. They produce organic acids that can break down the rock surface, leading to the formation of small cracks and crevices.

3. Soil formation: The broken down rock particles mix with the dead and decaying matter of lichens and mosses to form a thin layer of soil. This is a slow process that can take many years.

4. Creating a suitable environment for other species: As the soil layer thickens over time, it becomes suitable for the colonization of other plant species. These plants further contribute to soil development by adding organic matter through leaf fall and root death.

5. Ecosystem development: Over time, a diverse community of plants, animals, and microbes develop, leading to a more complex ecosystem. This process, from bare rock to a fully functioning ecosystem, is known as ecological succession.

In this way, lichens and mosses, as pioneer species, play a crucial role in starting the process of ecological succession on bare rock.