Define the terms Ecesis and Sciophytes.
In all the successions, the fundamental process involves the same procedures. The first step is “nudation”. The need of appropriate kind of habitat is the basic requirement for any community to grow and sustain. The bare area is required for any type of further growth. It can develop due to topographic conditions like soil erosion, land slide, volcanic activity, etc. or under the influence of climate like prolonged dryness, frost, fire, etc. sometimes the nudity is also achieved by biotic factors including deforestation, grassland cutting, overgrazing, etc.
Many a times with the change of climate the species of the area “migrate” to suitable communities through plant propagules, seeds, spores etc. and at the same time the change community act as a suitable place for other organism’s which “invade” the community.
Once the migration and invasion has taken place the need to establish themselves in the new environment arises. This adjustment with the new prevailing conditions is called “Ecesis”. It is considered to be complete when the plant is able to reproduce sexually.
By the mode of sexual reproduction each member of the species increases its number. Now as compared to the initial stages there is an increase in the number and is called ‘Aggregation’ . As a result of the aggregation each species and individual undergoes inter and intra specific ‘competition’ for water, nutrients, sunlight, carbon-dioxide, oxygen and space.
The species which are able to get through the struggle are considered successful. When the successful species modify the environment of the community it is called as ‘Reaction’. This is the most important stage of succession.
The environment which gets changed becomes unsuitable for the existing community and is gradually replaced by another community. The existing members move out of the community and are replaced by fresh migrants. This whole process results in the ‘stabilization’ of the existing vegetation which is in complete equilibrium with the complex environment at that place.
As long as the physical and climatic conditions of the place do not change the community is likely to persist. The soil is completely occupied by the plants and the community remains closed. This final community which is not easily replaced is called ‘Climax Community’.
The earth is tilted at an angle of 23 degrees 27 minutes, so the entire earth does not get equal quantum of sunlight at same time. From 22nd of March to 22nd September (Autumn Equinox) the North pole faces the sun and the sun shines for 24 hours over there, with South pole receiving no light and being in total darkness.
From 24th September to 20th March (Spring Equinox) the South pole has summers and North pole faces winters. Due to the specific nature of Plant life (on earth) being selective in growth depending upon availability of full or diffused sunlight, they have been classified as “Sciophytes’ (Shade loving) and Heliophytes'(Bright light loving). Plants more rigid in their preference are termed as `Obligate Sciophytes’ and ‘Obligate Helibphytes’ Some heliophytes can grow in shade and are called as ‘Facultative Sciophytes’ . Similarly, the Sciophytes growing in abundant light are called ‘Facultative Heliophytes’ .