Question

What is ecological succession? Explain the various stages involved in xeric succession hydric succession.

Answer 1

When a series of ecological communities are developed naturally in the same place till the formation of a climax community that doesn't develop further, it is called as ecological succession.

Xerarch succession: It is the succession that takes place in dry habitats like sand dunes, deserts etc, Plants growing in xerarch succession are called xerophytes.

Various stages by which xerarch succession develops are outlined below:

(1) Crustose lichen stage - Crustose lichens like Graphis, Rhizocarpon are thick and very resistant and grow on bare rocks as an external protective layer. They can tolerate extreme conditions and desiccation and can stick to the rock surface. The acidic substances produced by lichens results in the corrosion of rocks and formation of a thin layer of soil. The dead and decaying lichens then add humus to the soil making the habitat suitable for the growth of foliose(e.g. Parmelia) and fructose lichens.

(2) Foliose and fructose lichen stage: These lichens are leaf-like, soft and have a tender stem. They stick to the rock at one point only and increase shading due to their larger size. The dead organic matter forms humus, increases the moisture content of the soil and makes the soil suitable for the growth of mosses.

(3) Moss stage: Now that the habit is suitable, the mosses(e.g., Tortula, Grimmia) grow. They produce shade due to their larger size and replace the lichens. More soil accumulates as their roots penetrate deeper and the organic matter adds humus and moisture content to the soil.

(4) Herb stage: Small herbaceous plants now start to grow due to the presence of humus and moisture content of the cell. They pentrare their roots deeper secreting acids and weather the soil. Death of herbs adds more humus to the soil.

(5) Shrub stage: The habitat occupied by herbs soon become suitable for invasions of shrubs like Zizyphus and Rubus due to the presence of more humus. As shrubs are larger in size, their roots penetrate deeper, causing more fragmentation of rock and hence more soil accumulates.

(6) Tree Stage: Then woody trees begin to establish due to the increased moisture and humus content. The growth of tree species is supported by environmental change. The organic material like leaf litter and decaying roots add more humus to the soil.

(7) Forest stage/ Climax community: The succession stops in a forest which consists of many trees. It takes a very long time for the establishment of the climax community. The nature of the climax forest depends upon the climate of that area.

Hydrarch succession: It is the succession that takes place in wetter areas like freshly formed ponds. Plants growing in hydrarch succession are called hydrophytes.

Various stages by which hydrach succession develops are outlined below:

(1) Phytoplankton stage: It is the pioneer community of hydrarch succession when phytoplanktons grow in the pond as a result of the distribution of their spores by wind or animals. They multiply rapidly and zooplanktons feed upon them. The death and decaying plankton forms mix with clay and slit at the bottom of the pond to form soft mud. Then the next stage grows.

(2) Submerged stage: Here, the pond becomes shallower and nutrients are moderate in amount. These plants are submerged in water and their death adds organic matter to the bottom level which then rises and provide space for floating leaves hydrophytes.

(3) Floating stage: Here, the pond becomes more shallower and the leaves of the rooted plants in mud float in water.

(4) Reed swamp stage: More shallowing of plants occur due to continued siltation which paves the way for the growth of rooted emergent plants i.e., reeds(amphibious plants).

(5) Marsh-meadow stage: Reed swamp stage is invaded by marshy plants. With increased settling of silt and deposition of dead organic matter derived from floating and rooted species, the pond becomes shallower until it gets transformed into terrestrial habitat. E.g., Carex, Juncas.

(6) Scrub stage: Marsh-meadow stage is replaced by shrubs. E.g., Salix, Populus.

(7) Climax community: The scrub stage is replaced by trees which grows to greater heights. The nature of climax community depends on the climate of that area. E.g., Forest.