Xerosere Succession, 6 Stages and Diagram

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DEFINITION

A succession beginning in a dry area is known as xerosere.

XEROSERE SUCCESSION

Xerosere is initiated on bare area like rocky lands, sand or stony lands and is characterised by extreme deficiency of water in soil. It also shows a few stages of development.

XEROSERE SUCCESSION STAGES

(a) Crustose lichen stage

In this stage the rocky habitat is extremely xeric, there is no water and nutrient in the substratum. The surface temperature becomes very high when exposed to sun.

In such a habitat only the crustose lichens which have the ability to bear high degree of extreme temperature and desication can grow. Lichens are carried to the bare rock through wind-borne soredia, spores, lichen fragments etc.

(b) Foliose lichen stage

This type of lichens attach with the surface rock near or around the region already occupied by crustose lichens. They are attached to the rock by the margin or a single point. As a result crustaceous lichens are often killed.

In humid and warm tropical areas both crustose and foliose lichens are replaced by nitrogen-fixing blue-green algae (Scytonema). Parmella, Dermatocarpon, etc are common foliose lichen of this stage.

(c) Moss stage

In this important stage the surface of the rock is covered by a continuous layer of soil. In this stage spores of xerophytic rock mosses are carried on the rock surface by air currents.

Hydrosere Succession

Spores germinate during the rainy season around the crevices occupied by the foliose lichens. The rhizoids of the moss plants compete with those of foliose lichens for the absorption of water and nutrients, leafy shoots of mosses, also shade out foliose lichen thalli.

In this way, moss plants become dominant in this stage. Common mosses in this stage are Polytrichum, Bryum, Grimmia, Fissidens, etc.

(d) Herbaceous stage

Moss plants constitute mat vegetation over the rock surface and as such they retain water after a rain. This condition helps the germination of seeds of short-lived and xerophytic grass and other herbs.

Here the herbaceous plants grow quickly and shade the moss plants completely. The herbaceous plants include the species of Poa, Festuca, Eleusine, Justicia, Tridax, Lindenbergia, etc.

(e) Shrub stage

In this stage, xerophytic herbs are followed by xerophytic shrubs. Shrubs are brought to the area by rhizomes, or seeds from adjoining area.

The common pioneer shrubs of this stage are species of Fragaria, Rubus, Zizyphus, Capparis, Zygophyllum, Rhus, etc.

(f) Climax forest stage

In this stage climax type of forest formation results with the formation of reasonably thick layer of soil and humus due to decay of different plant-groups in previous stages.


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