Q.Starting from the pioneer species, trace the sequence that follows in an ecological succession on a bare rock, until climax community is reached in an ecosystem. Name this type of succession.
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Start your 14-day free trial to unlock the full solution →The sequence from pioneer species to climax community on bare rock is lithosere (a type of xerosere), progressing through crustose lichens → foliose lichens → mosses → annual grasses → perennial grasses → shrubs → trees → climax forest.
The Concept: Why Succession Happens on Bare Rock
Ecological succession is the orderly, predictable change in species composition over time in a habitat. On bare rock, the challenge is extreme: no soil, no water retention, intense temperature swings, and no organic matter. The only organisms that can survive here are pioneer species — hardy life forms that can colonise the inhospitable surface and, through their own life processes, begin to break down the rock and create the first thin layer of soil.
This specific type of succession, starting on a bare rock surface, is called lithosere (from Greek lithos = rock). It is a sub-type of xerosere (dry habitat succession). Each stage modifies the environment, making it slightly more favourable for the next, more complex community, until a stable climax community — typically a forest in a humid climate — is reached.
A common mistake is to confuse lithosere (rock) with hydrosere (water) or psammosere (sand). The key is the starting substrate: bare rock means lithosere.
Step-by-Step Sequence
The entire process can take hundreds to thousands of years. Here is the typical sequence:
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Crustose Lichens (The True Pioneers)
These are the first colonisers. Crustose lichens are flat, crust-like organisms that cling tightly to the rock surface. They secrete acids (carbonic and organic acids) that chemically weather the rock, and their hyphae physically penetrate tiny cracks. This begins the slow process of soil formation. They also trap wind-blown dust and organic debris. The rock surface is now slightly rougher and has a microscopic layer of organic matter.
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Foliose Lichens (The Leafy Stage)
Once a thin layer of soil exists, foliose (leafy) lichens can establish. They are larger and more efficient at trapping moisture and dust than crustose lichens. Their broader surface area shades the rock, reducing temperature extremes. As they die and decompose, they add more humus, deepening the soil layer. Eventually, they outcompete the crustose lichens for space.
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Mosses (The Soil Builders)
Mosses are small, non-vascular plants that require a thin but continuous film of moisture. The soil created by lichens now holds enough water for them. Mosses have rhizoids (root-like structures) that further break the rock and bind the soil. Their dense mats trap even more dust and organic matter, and they retain water far better than lichens. The soil layer becomes thick enough to support plants with true roots.
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Annual Grasses and Herbs (The First Vascular Plants)
With a recognisable soil layer (perhaps a few centimetres deep), fast-growing annual grasses and herbaceous plants can germinate. Their root systems penetrate deeper, further breaking the rock and aerating the soil. They add substantial organic matter when they die each year. This stage is still unstable — the soil is shallow and nutrient-poor — but it is a major transition.
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Perennial Grasses and Herbs (The Sod-Forming Stage)
Perennial grasses have deeper, more extensive root systems that form a dense sod (a mat of roots and soil). This sod holds the soil together, prevents erosion, and retains moisture much better. The soil now has a distinct A-horizon (topsoil). Competition for light and nutrients becomes intense, and the annuals are gradually shaded out.
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Shrubs (The Woody Invaders) …
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