Every community has an appear- ance of itself called physiognomy. This is nothing but the form and structure of the vegetation. We use the terms like forest, grasslands to describe the physiognomy of a community. Physiognomy is usually the manifestation of the life form of predominant plants.
B. Species dominance
Though a community has a variety of species, only a few species are rela- tively abundant and are called ecological dominants. The physiognomy of the community is usually the reflection of the dominant species.
The abundance may be in number or biomass. Casuarina forest, sal forest etc., are examples of forests where a particular species is dominant. On the other hand, evergreen forest, deciduous forest etc., are examples, where evergreen and a deciduous plants are in dominance.
C. Specics diversity
A community is an assemblage of plant, animal and microbial species in a particular area. The number of species in a community indicates how diverse the community is. More the number of species, higher is the diversity. A community is more stable when its species diversity is high. Species diversity remains on the higher side when the conditions are as follows:
(i) Stable but complex and heterog- enous environment;
(ii) Older age of the community;
(iii) A few individuals representing each species with the more number of species; and i
(iv) Higher ecological amplitude (the range of environment a species can tolerate)- Presence of ccrtain types of species in a community may act as ecological indicators. For example, presence of Utricularia in a pond indicates water pollution.
Following arc two examples of vertical stratification:
(i) In a grassland community the strata could be the roots and rhizomes, the ground layer and the herbaceous layer.
(ii) In a forest there are five vertical subdivisions – subterranean zone, forest floor, ground vegetation (up to a metre), shrub layer, tree layer (top storey). The strata of a forest community are dependent on light penetration (Fig 30.13). Horizontal stratification, which oan also be called dispersion, may be (i) random (ii) clumped or (iii) regular
Succession is a dynamic characteristic of a community. A community goes on changing until a balance is established between community and environment. The equilibrium state is called climax. Continuous change (succession) and climax are characteristics of a community.
Besides the above characteristics, a community also shows certain features when considered along with other communities. Different communities under similar environmental conditions show ecological equivalents (organisms of different species but showing same type of adaptations due to their exposure to similar environment).
When one community merges into another, the transition zone is called the ecotone zone of transition. An ecotone shows edge effect (presence of greater diversity along with members of both communities).