Growth forms/Life forms and structure of community

1.     Growth forms/Life forms and structure of community

A community consist of different growth form determining the community structure such as herbs, shrubs, trees. A growth form also have variations such as a tree can be long leaved or broad leaved etc. various growth form have different mode of arrangement classifying community into (a) Vertical stratification and (b) Horizontal Zonation, i.e. Populations assembled to form communities and these populations are dispersed into definite vertical or horizontal strata.

a.     Zonation

The spatial arrangement of community species exhibit patterns dividing it into sub-communities which are ecologically related. If the distribution pattern is horizontal it’s called zonation layering in community. For example in lakes or deep ponds majorly three zones are recognised i.e. littoral, limnetic (Photic or open-water) and profondal zone (Aphotic or Deep-water). The organism varies in each zone of zonation pattern. Another example include mountain associated vegetation, altitudinal and latitudinal variations of vegetation in relation to climate of the existing region.

A mountain depicting a horizontal zonation

b.     Stratification

Vertical change in the pattern of community structure is called stratification. Stratification can be simple such as in the horizontal zonation community of pond each zone has different vertical storey, or complex stratification. For example in grassland communities distinct floor with different yet characteristics growth forms are exhibited. The lowest vertical sub-division is called (1) subterranean, which includes roots of plants, debris and living organisms like soil bacterium, protozoas or fungi etc.

(2) Herbaceous substratum: Above the soil with roots of growth forms, the herbaceous sub-stratum includes upper parts of growth forms. The forest community stratification is much more complex with five vertical layering including:

1. Subterranean-beneath the soil

2. Forest floor-with the upper parts of growth form along with the litters, fungi, bacteria etc.

3. Herbaceous vegetation

4. Shrubs

5. Forest Strata (canopy)

Forest animal’s lives in different substrata and many of them may shift between substratums. The properties (requirement and adjustments) of one stratum can be similar to the same stratum of different community somewhere else in the world. For example forest floor of one community in country 1 share common requirements and adjustments to the community in country 2 although these countries are geographically separated.

The animals living in such geographically separated but similar substratum are called Ecological Equivalent.