Ecosystem — BIOLOGY STD 12 Science — Question

There are six stages of xerosere are :
I. Progressive stage/Crustose Lichen stage,
II. Layered lichen
III. Flesh stage
IV. Herbaccous stage
V. Pole stage/Shrub stage
VI. Climax vegetation
I. Progressive Stage or Crustose : Crustose lichen like Rhizocarp, Liconosh, etc. grow first on exposed rocks. Acids secreted by lichens weather the rocks.
II. Foliose Lichen Stage : Foliose lichen like Palmelia, Physalia, Dermatocarp grow on a thin layer of soil. After this death, a thick layer of soil and organic matter is jormed.
III. Moss Stage : A thick layer of soil and humus on the rocks makes it suitable for moss. In this stage Polytrilum. Tadla, Funiraryops, grow successfully. Due to the continuous decomposition of bryophtes, a thick layer of organie matter is formed on the rocks. Now the habitat starts becoming suitable for ferbaceous plants.
IV. Herbaseous Stage : When the habitat become suitable for herbaseous plants, herbaceous plant like Poa, festuca, Tridex, Ageratum etc grow. The rocks are continous by weathered. as a result, the invasion of shrubby plants begins.
V. Bushy Stage : Due to the formation of thick layer of humus—rich soil on the rocks, bushy plants start growing among the herbaseous plants, such as cassia, Urena, Crotalaria. Due the growth of bushes, the rocks start turning into soil and the encroachment of trees begins.
VI. Climax Stage : Desert trees start increasing, these trees maintain a balance with their habitat, as a result of which forest area develop; the community of trees is almost a permanent community.