Question

Lichen is the pioneer vegetation on which succession?
(a) Hydrosere
(b) Lithosere
(c) Psammosere
(d) Xerosere

Answer 1

Any succession has its beginning and end points interspersed with sub- stages in between. The pioneer species marks the beginning of a succession. Lichen is the pioneer vegetation of a succession that begins its journey in a water- scarce habitat.

Complete step by step answer:
Succession includes a unidirectional series of changes in community composition on an ecological time scale that finally leads to the establishment of a stable community known as a climax community. Pioneer vegetation are the first ones to colonize any unoccupied or barren land and thus initiate primary succession. Succession initiated with the establishment of pioneer communities in drier areas is known as xerarch and its every successional stage is known as xerosere. The pioneer communities in xerarch succession are lichens which are the symbiotic association of fungi and algae.
- The hydrarch succession may take place in freshwater ecosystems such as ponds, lakes, etc, or in saline water ecosystems such as mangroves, estuaries.
- The xerarch succession can be further subdivided into Lithosere and Psammosere. When succession takes place on bare rocks that may be produced when a volcano erupts or by glaciers, it is known as lithosere while in Psammosere, the succession takes place in a sandy area like sand dunes.
- E.g. In Lithosere, cracks and crevices appear in the rocks which are further filled by soil particles. The spores of algae and fungi carried by wind form lichens and occupy these crevices.
- These pioneer species accumulate dust particles and retain water. They also secrete acidic secretion. All this helps in further solubilization of the rocks into fine particles.
- Their decomposition enriches the new soil with humus and thus paves way for the future plants and animals.
So, the correct answer is ‘Xerosere.’

Note:
- Succession in areas such as a new volcanic island or a bare rock exposed, where no community existed before, is known as primary succession.
- Secondary succession occurs at a site where an already developed community has been destroyed by some natural disasters such as fire, flooding, or by any human activity and a series of communities subsequently develops at that site.