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Question 45 of 46

Q.i) Name the pioneer species on a bare rock.

ii) How do they help in establishing the next type of vegetation?
iii) Mention the type of climax community that will ultimately get established.
West Bengal WbchseWest Bengal HS (WBCHSE) Board 2026Subjective· 3mImportance★★★★★
98% · 45/46 Questions
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On bare rock the pioneers are lichens; by weathering the rock and adding humus they build soil for later plants; the final, stable climax community on land is a forest.

This question describes primary ecological succession (xerarch succession) on bare rock:

i) Pioneer species: the first organisms to colonise a bare rock are lichens (a symbiosis of fungus and alga), because they can survive with almost no soil.

ii) How they help the next vegetation: Lichens secrete organic acids that chemically weather and dissolve the rock surface; their growth and death add organic matter (humus). This slowly produces a thin layer of soil, which can then hold water and support the next colonisers — first mosses, then herbs, grasses, shrubs and finally trees. Each stage further deepens and enriches the soil for the next.

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