(a)(i) What is ecological succession? (ii) Describe the process of ecological succession on a bare plot of land. (b) Explain the following terms: (i) biosph...

(a)(i) Ecological succession

Ecological succession is the gradual and orderly replacement of one community of organisms by another in an area over time, until a stable climax community in equilibrium with its environment is established.

(a)(ii) Ecological succession on a bare plot of land

The succession may be represented as follows. The rising curve shows the gradual increase in vegetation biomass, soil depth and complexity of the community from the pioneer stage to the climax stage.

1. A bare plot is first colonised by pioneer organisms such as algae, lichens and mosses which can tolerate harsh conditions.
2. As the pioneers grow and die, their remains decay and add humus and mineral nutrients to the surface. Their activities also help to break down the surface and form a thin soil layer.
3. The improved soil retains more water and supports grasses, herbs, ferns and small animals such as insects and worms.
4. Continued death and decay of organisms make the soil deeper and more fertile. Perennial grasses are then replaced by shrubs and small trees.
5. Eventually, large trees and a greater variety of animals, including birds and mammals, become established.
6. A stable climax community, such as a forest where climatic conditions permit, is finally formed. It remains in dynamic equilibrium with the environment.

(b) Explanation of terms

(i) Biosphere: the parts of the earth, including land, water and air, in which life exists.

(ii) Population: all the organisms of the same species living in a particular area at a given time.

(iii) Community: all the populations of different species living and interacting in the same habitat.

(iv) Ecosystem: a functional natural unit made up of living organisms and their non-living environment interacting with one another.

(c) Instruments