The populations of different species living in the same habitat is called community. According to Oosting (1956). plant community is an aggregation of individuals with mutual relationships among themselves and to their environments. Thus community has two parts:
- Mutual Relationship among Individuals
It includes all the direct or indirect effects of the organisms on each other. Competition is the most important effect. A forest is composed of different kinds of plants. It has huge trees, large shrubs, small shrubs and ground flora etc. Survival of lower layer of plants depends upon the shade of the trees above them. The huge trees provide adaptation for the undergrowth.
Fungi and bacteria are also a part of the community. The also play an important role. These fungi and bacteria may be parasitic or saprophytic. They cause many diseases. Some of these diseases become much serious. These diseases can destroy whole community. There are certain symbiotic bacteria. They form a small nodule on the roots of the leguminous plants. These nitrogen fixing bacteria take free nitrogen from the air and combine it with other elements. They form nitrogenous compounds for the plants. The nitrogenous compounds of the plants are released in the soil. They are used by other plants.
2.Mutual Relationship with the environment
The plants adapt themselves in their habitat. Some plants can withstand heat or cold. Some plains require a large. continuous supply of moisture. But some other plants require only a small amount of moisture. Thus the climate of a region controls the kind of plants. The complex of climatic factors determines the general vegetation types like grassland or forest. Thus climate of a region call he evaluated by observing the vegetation.