1. Plant formation:
When vegetation reaches the highest development, becoming stable for more or less definite period, under existing climate, it is called plant formation. Dominant members of a plant formation have similar growth forms.
In a deciduous forest formation, all dominant species are broad- leaved trees. Principal formations of world are rain forests, deciduous forests coniferous forests, grasslands, deserts and mangroves.
Community with two or more dominant species is known as association. Developmental or serial communities of association are known as associes. Two sub-divisions of association are (a) Fasciation: Local variants of association, which are related within a general climate develop small difference in moisture relations and temperature. Serai communities are accordingly known as fades. (b) Lociation: An association having different types of some main sub-dominant and chief secondary species. Serai communities are known as locies.
Community with a single dominant species is known as consociation. In one association, many consociations may be present. Serai communities of a climax consociation are known as consocies.
A community characterized by one or more sub-dominant species. Serai communities are known as socies. Societies are of two types:
(a) Aspect society: It is found in places with marked seasonal variations, where different species appear in different periods of their vegetative growth and flowering.
(b) Layer society: Under influence of dominant species, trees of forest formation develop one or more layers of shrubs, followed by layers of herbaceous communities. A ground community of society of mosses, a lichen, etc., in forest is also present.