3. Temperature
• Variable factor influenced by time, season, latitude, altitude, slope, soil
texture, plant cover and human activities
• Penetrates every region of biosphere and influence all forms of life
• Is a measure of intensity of heat
• Expressed in Fahrenheit or Celsius (Centigrade)
• Heat – thermal energy
• Thermal energy is exchanged between organisms – radiation, conduction,
convection and evaporation
• Estimation of thermal energy flow in biosphere – heat budget
4. • Direct temperature effects on vegetation:
• Affects physiological processes – thus growth and size
• Determines survival of species in particular region – tolerance to temperature
range
• At 40 °C – minimal to plant life
• At 90 °C – plant die
• Below freezing point – crystallization of protoplasmic water
• Vegetation existence – 26 °C – conifers, 66 °C – desert plants
5. Classification of plants based on heat requirements:
• i) Megatherms – plants of warm habits – require high degree of heat
throughout year – found in tropical climates e.g., deserts
• ii) Mesotherms – plants of habitat which is neither too hot nor too cold. These
cannot withstand extreme temperatures – hence found in tropical and
subtropical regions
• iii) Microtherms – plants of cold or temperate habitats, cannot tolerate high
temperature. Can be found in tropical and subtropical areas at high elevation
• iv) Hekistotherms – plants of cold and alpine regions, do not thrive well in
heat, can withstand long and severe winters
6. • Respiration rate get doubled – at
increase of 10 °C above optimum
temperature – other factors needs to be
favourable – Van’t Hoff law
• High temperature favours growth of
plants – but for some crop plants low
temperature is beneficial
• Vernalization – process by which
temperature range of plant is lowered
to get early crop
• Temperature fluctuations
• Fluctuates daily and seasonally
• Governed by brightness of sun
• With increase of every 150 m altitude,
temperature decrease by 1 °C
• Varies with different habitats
7. Thermal stratification
• Process of fresh water habitat
differentiation on the basis of
vertical changes of temperature into
three strata
• Classification of fresh water media
into three layers:
i) Epilimnion – superficial layer of
water body – constantly stirred with
wind – warm water
ii) Metalimnion or thermocline –
intermediate zone between upper and
bottom layers of water body – shows
temperature fluctuation
iii) Hypolimnion – bottom layer of
stagnant water – little or no
fluctuation in temperature
8. References
• Shukla JP, Pandey A and Pandey K. 2009. Environmental
Biology and Ecology. Narendra Publishing House. 7-22.
• Ambasht RS and Ambasht NK. 2000. A Textbook of Plant
Ecology. 13th edition. SK Jain for CBS Publishers and
Distributors, New Delhi.
