Raunkiaer classified the world's vegetation into the following 4 types based on the temperature prevailing in an area.
(i) Megatherms
(ii) Mesotherms
(iii) Microtherms
(iv) Hekistotherms.
In thermal springs and deep sea hydrothermal vents where average temperature exceed `100^(@)C`. Based on the range of thermal tolerance, organisms are divided into two types.
(a) Eurythermal : Organisms which can tolerate a wide range of temperature fluctuations. Example : Zostera (A marine Angiosperm) and Artemisia tridentata.
(b) Stenothermal : Organisms which can tolerate only small range of temperature variations. Example : Mango and Palm (Terrestrial Angiosperms). Mango plant do not and cannot grow in temperate countries like Canada and Germany. Thermal Stratification : It is usually found in aquatic habitat. The change in the temperature profile with increasing depth in a water body is called thermal stratification.
3 kinds of thermal stratifications:
(i) Epilimnion - The upper layer of warmer water.
(ii) Metalimnion - The middle layer with a zone of gradual decrease in temperature.
(iii) Hypolimnion - The bottom layer of colder water.
Temperature based zonation :
Variations in latitude and altitude do affect the temperature and the vegetation on the earth surface. The latitudinal and altitudinal zonation of vegetation is illustrated below: Latitude : Latitude is an angle which ranges from `0^(@)` at the equator to `90^(@)` at the poles. Altitude : How high a place is located above the sea level is called the altitude of the place.
Timber line / Tree line : It is an imaginary line m a mountain or higher areas of land that marks the level above which trees do not grow. The altitudmal hmit of normal tree growth is about 3000 to 4000m.
