Ecologically, the terrestrial habitat is sub-divided into a number of sub-units called biomes. A biome is defined as a major terrestrial community characterised by distinctive plants and animals. Example I. Forest Biome, II. Grassland Biome, III. Desert Biome.
1. A biome is a major terrestrial community.
2. It is formed of distinctive animals and plants.
3. Each biome has a climax community which is dominant. The climax community forms the matrix of the biome. The biome is named after the climax community. For example, in a grassland biome, grasses form the climax community. In a forest biome, trees form the climax community. There is no clear-cut demarcation between adjacent communities. A biome is different from an ecosystem, in that the ecosystem consists of both biotic and abiotic factors. But a biome includes only plants and animals.
A forest biome is a land of thick growth of trees. The development of forests is conditioned by a number of climatic factors, such as temperature, rainfall, availability of space and humidity.
Based on the types of plants and geographical location, forest biomes are classified into three types, namely
1. Coniferous forest
2. Tropical rain forest
3. Deciduous forest
This biome is thickly populated with pine trees characterised by needle-like leaves belonging to the class of Gymnosperms. The leaves of the trees are evergreen. They are restricted to northern hemisphere. Heavy rainfall and humidity are the climatic features of this forest. It is also called 'Taiga' because it gives thick shade and prevents the growth of herbs and shrubs. The seeds of pine trees form the major source of food for certain animals.
Flora: Pinus, Cedrus and Cupressus
These forests are found in the tropical zone of the world where very high temperature and abundant rainfall is seen. Trees are very high with woody stems. The leaves are broad and evergreen. In this forest the productivity is very high. It is formed of three layers namely an upper layer of leaves and branches, a middle layer of shrubs and small trees and a lower layer of forest floor.
Flora : Bauhinia, Bambusa and Sterculia
These forests are found in India, Australia, Europe and U.S.A. This forests have tall trees with broad and thin leaves which fall during winter. During summer the days are long and the climate is warm. During winter the days are short and climate is cold. During autumn the trees shed their leaves and remain in dormant condition.
Flora : Teak, Shorea and Terminalia
This type of habitat is seen in major part of the world (North America, Asia, Siberia, Russia and Africa). The plain lands are occupied by grasses. Grasses form the climax community in this biome. Grassland biome is also called Prairies, Steppes, Pampas etc. Rainfall is irregular with strong winds which help to increase dryness and avoid the growth of trees.
Flora : Andropogon, Saccharum and Cenchrus
A desert is a waterless, treeless, large waste land and often covered with sand. Scarcity of water, extreme temperature and dust storms are the characteristic features of this biome. Deserts are classified into two groups, namely hot-deserts and cold deserts. In hot deserts the temperature is very high. (eg.) Sahara, Kalahari (Africa), Rajasthan (India) and Gobi (China). In cold deserts, the temperature is very low. They are situated at high altitudes. (eg.) Tibet, Alps, Scandinavian mountains etc.
Flora : Opuntia (Cacti), Zizyphus and Calotropis