“The effective climatic, Edaphic, Topographic and Biotic conditions of a site, which influence the vegetation of the locality”.
The condition of the atmosphere at a particular location over a long period of time (from one month to many millions of years, but generally 30 years). Climate is the sum of atmospheric elements (and their variations): solar radiation, temperature, humidity, clouds and precipitation (type, frequency, and amount), atmospheric pressure, and wind (speed and direction). To the non-specialist, climate means expected or habitual weather at a particular place and time of year. To the specialist, climate also denotes the degree of variability of weather, and it includes not only the atmosphere but also the hydrosphere, lithosphere, biosphere, and such extraterrestrial factors as the sun._ LoF
· Although eastern and western aspects receive about the same insolation, the angle of incidence is highest on the eastern slopes in the morning when the dew is still on the ground.
· Southern aspects receive more solar radiation than northern.
· Western and south-western aspect receive a max amount in the afternoon when cooling effects of night conditions have been lost, in contrast to the eastern and south-eastern aspects where insolation is maximum in the morning.
· Altitude has a much greater affection temperature than has latitude.
· The mean annual decrease in temperature with an increase in elevation has been calculation as 10F per 400 feet in N.W. The Himalayas.
· The air near the earth’s surface is warmed by absorption of insolation and radiate heat’s from the earth.
· With increasing altitude the atmosphere becomes less dense and also contains less moisture and other heat-absorbing substances.
· Consequently the temperature declines with the altitude.
· Variation of M.A.T. with Altitude:-
MEAN ANNUAL (F)
When the atmosphere is in motion, however, the winds may transport the air from one place to another and the heat thus transported may mask the effect of local solar radiation and altitude. E.g. the frequent cold waves experiences in Pakistan during winter as a result of the influence of cold winds from Central Asia.
o HEAT REQUIREMENT OF PLANTS
· According to the heat requirements of plants, RAUNKIAR divided the gross vegetation into the flowing types:-
These are plants of warm habitat which require a high degree of heat throughout the year e.g. of tropical climates.
§ Plants of deserts
§ Equatorial and Tropical Region Rain Forest.
These are plants living in the high temperature of summer, alternating with a low temperature of winter e.g. They are found in deciduous forests of tropical and sub-tropical regions.
These are the plants of cold or temperate habitat and require low temperature for their growth.
Such plants cannot tolerate high temperature.
They may also be found in tropical and subtropical areas at high Elevations where temperature conditions are less extreme.
These are the plants of cold and Alpine regions. They do not thrive well in heat and can withstand long and very severe winter.
1. Many plants are very sensitive to temperature. The sudden fall in temperature is injurious because plant tissues are badly affected by it.
2. Forests suffer from night frost on the east side when the sun rays strike very early in the day.
3. The temperature stimulates the growth of seedlings.
4. The optimum temperature for seed germination ranges between 200c and 270c.
5. Photosynthesis operates over a wide range of temperature.
6. Most of the ALGAE require lower temperature range for photosynthesis than the higher plants.
7. The photosynthesis continues even at 800c in some desert plants.
8. The rate of respiration increases with the rise of temperature up to a certain level, but the optimum limits the respiration rate shows marked decrease.
9. Temperature determines the grow of many plants. Cotton prefers high temperature, Potato gives highest yield in low summer temperature.
10. Growth of plants is retarded at high temperature.
11. Temperature in combination with humidity and other factors helps in the spread of diseases in plants.
12. Low temperature and high humidity favour the Rust attack.
13. Low temperature, high humidity and cloudy weather favour the damping-off, seedling blight, foot rot and root-rot diseases of Cucurbits, Tobacco, Papaya, and Ginger.
14. Temperature is the most influential climatic factor in affecting the distribution of Plants.
15. The temperature is highest at the EQUATOR and it gradually falls down towards the ARCTIC.
16. Due to difference in temperature, Tropical, Sub-tropical, Temperate and Alpine vegetations have been formed.
17. The temperature determines the flora of a particular region.
18. The distribution and habitat of species is their main features are determined by heat or temperature.
· Temperature of a place depends upon its latitude and altitude.
· Generally mean temperature of air decreases about 50c for every degree latitude North of equator and for every 300 feet of Altitude.
· Temperature also depend upon plant cover, water content of the soil, physiographic features like steepness and exposure of the slope and direction of mountains.
· In terrestrial environment temperature fluctuations are varied and marked.
· Desert plants grow in extreme heat, Aquatic plants grow in low temperature range and grasses prefer to grow in the area of moderate temperature.
· Temperature in combination with moisture determines the general distribution of vegetation. Northern, Southern, Tropical and Temperate vegetation depend solely upon temperature and moisture.
o THE IMPORTANCE OF TEMPERATURE
1. Temperature influence the actual amount of water vapor present in the air and thus decides the moisture carrying capacity of the air.
2. It decides the rate of evaporation and condensation and therefore grows the degree of stability of the atmosphere.
3. As relative humidity is directly related to the temperature of the air, it affects the nature and types of cloud formation and precipitation.
o FACTOR INFLUENCING TEMPERATURE
4. Ocean Currants and Winds
5. Slope, Shelter, and Aspects
6. Natural Vegetation and Soil
7. Cloud Cover
Temperature thus diminishes from equatorial regions to the poles. e.g. Due to earth inclination, the mid-day sun is almost overhead within tropics but the sun’s rays reach the earth at an angle outside the tropics.
Since the atmosphere is mainly heated by conduction from the earth, it can be extracted that places nearer to earth’s surface are warmer than those higher up. Thus temperature decreases with increasing height above sea-level. A fall of 0.60c occurs with an assent of 300 or 10c per 164 meters. It is usually more in summer than in winter.
Land surface is heated more quickly than water surface because of the higher specific heat of water.
4. Ocean Currents and Winds
Both ocean currents and winds affect temperature by transporting their heat or coldness into adjacent regions.
5. Slope, Shelter, and Aspects
- A steep slope experiences a more rapid change in temperature than a gentle one.
- Mountain ranges that have an East-West alignment like the Alps show a higher temperature on the south-facing “Sunny slop” on the north-facing “shelter slope”.
- The temperature may be lower in the valley than higher up the slopes.
6. Natural Vegetation and Soil
- Cool in the Jungle and its shade temperature is a few degrees lower than that of open spaces in the corresponding latitude.
- During day trees lose water by evapotranspiration so that the air above is cooled. Relative humidity increases and mist and fog may form.
7. Cloud Cover
Clouds thick cumulus and stratus clouds after the temperature of a place by absorbing the incoming solar radiation in the day and blanketing the out-going radiation heat of the earth.
o WATER FACTORS
- Water covers nearly three-fourths of the Earth surface. The different phases of water circulation are:-
1. Precipitation in the form of rain or snow.
2. Immediate return to the atmosphere by the process of evaporation.
3. Evaporation from different water bodies like seas, rivers etc.
4. Transpiration processes in Plants.
5. Transpiration processes in Animals.
6. Drainage by means of underground channels, streams, and rivers, which ultimately reaches the ocean. This cycle has been termed the water or Hydrological cycle.
- Rainfall is the main constituent of precipitation.
o TYPES OF WATER
- Water is used in vegetation by various means; some of them are being described below:-
i. Atmospheric moisture
iii. Soil Moisture
i. Atmospheric Moisture
(A) Invisible vapours (Humidity).
(B) Visible vapours (Cloud and Fog).
(A) Invisible vapors
§ A certain amount of water is present in a vapor state in the atmosphere.
§ It is believed that a total of 0.1 gm to 40 gm of water is present in each kg of Air.
§ Moisture which is present in the air in water vapor form is termed as HUMIDITY.
§ This has a direct bearing on the nature of transpiration, which in turn determines the suitability of a plant to grow in a particular habitat.
· Absolute Humidity
§ It is the actual amount of water which is present in the air and is expressed in units of gms/cubic meter or grains/cubic feet of air.
§ The following factors affect humidity:-
i. Existing air temperature
ii. Existing wind speed
iii. Altitude at which the observation is made.
iv. Exposure and aspect of the locality
v. Vegetation cover of locality.
vi. Soil moisture content.
§ To a layman, it may seem as if the air is dry but actually it may not be so for in a given unit of air space in desert areas, the quantity of moisture present may be more than that in other regions. Hence the term relative humidity has been brought into usage.
· Relative Humidity
§ It is defined that the quantity of water vapour in the air exposed as the percentage of the quantity of the same which the air can hold at the existing temperature.
§ Boiling point = 1000c
§ Melting point = 0.000c
Ø The condensation of water vapor in the air due to the cooling is called precipitation.
Ø Hail or Sheets
Ø Ice or Glaze
Condensation of water vapour in participles sufficiently small to remain suspended in the air above the ground.
Condensation of water vapour in participles sufficiently small to remain suspended in the layer of air near the ground.
Condensation of water vapour directly on the cooled surface.
Condensation takes place above the freezing point.
Condensation takes place to blow the freezing point.
Ø Hail or Sheets
Rain that freezes as it falls through such freezing air layers.
Ø Ice or Glaze
Rain if freezes as it falls on a sub-freezing surface.
Ø Among all the environmental factors which affect the distribution and growing of plants, water is considered to be the most important because it is essential for all life process.
Ø What is a very important nutrient for protoplasm, about 80% of water is present in the living cell.
Ø It is essential for maintains of turgidity.
Ø It acts as solvent through which gases and minerals are absorbed by the plants.
Ø All the physiological processes such as photosynthesis, transpiration, and translocation of food material also take place with the help of water.
Ø Water also plays an important role in pollination and fertilization of flowers and dispersal of seed & fruits.
Ø Water covers about 73% of earth’s surface occurring in ponds, lakes, streams, and oceans etc.
Ø It falls from the atmosphere in the form of precipitation and is also present as atmospheric humidity.
Ø In Nature water moves in more of the less circular path called Hydrological cycle.
o ADAPTATION OF PLANT COMMUNITIES TO WATER
Ø Most of the plants are adapted in nature according to the amount of moisture available to them. Thus plants may be present in habitat with an abundance of water.
o HYDRIC HABITAT
Such as River, Ponds, Lakes, Stream etc. They may grow on the moist and swampy banks.
o AMPHIBIOUS HABITAT
Plants may also grow in between the scarcity and abundance of water or mesic habitat.
o XERIC HABITAT
Ø Plants are also found in PHYSICALLY DRY or PHYSIOLOGICALLY Dry localities – xeric Habitat.
Ø Depending upon the habitat, plants have adapted themselves morphologically and anatomically and accordingly they are classified into the following Ecological groups.
§ Hydrophytes are the plants which grow in water reservoirs like Ponds, Lakes, Streams or Rivers.
§ They are grouped as follows:-
1. Submerged hydrophytes
2. Free-floating hydrophytes
3. Fixed Floating Hydrophytes
1. Submerged Hydrophytes
· These plants are fully submerged in water.
· They are found in tanks, ponds, pools, rivers, streams & lakes e.g.
2. Free Floating Hydrophytes
· Free-floating plants are not anchored in the soil but are freely swimming over the water surface. e.g.
3. Fixed Floating Hydrophytes
· These hydrophytes are anchored in the soil and their leaves are floating on the water surface.
· They occur in shallow water with well-developed roots which are fixed in the mud. e.g.
iii. Victoria regia
§ Amphibiophytes or moisture-loving plants are the emersed plants which grow on very moist and swampy places i.e. on the side of ponds, ditches, streams, rivers, lakes shallow and muddy water etc. e.g.
i. Ranunculus richophyllous
ii. Sagittaria sagittifolia
vi. Arundo donax
viii. Livers worts
xi. Begonia etc.
§ These are the land plans which grow in habitats which are neither dry nor wet and the temperature of the air is neither too high nor too low.
§ They avoid waterlogged and saline soil.
§ Thus they love to live in habitats which are in between the two extremes i.e. Scarcity of water and abundance of water.
§ Therefore mesophytes are the plants which are intermediate between xerophytes and hydrophytes.
§ Xerophytes are the plant living in the xeric habitat.
§ Xeric habitat is an area with inadequate water physically dry habitat such as found in arid regions, on rocks, gravelly and sandy soils or on steep slopes.
§ They are further classified into the following sub-groups:-
i. Drought avoiding xerophytes
ii. Drought resisting xerophytes
iii. Drought enduring xerophytes
§ Xerophytes growing in the physiologically dry habitat are subdivided into the following groups:-
2. Alpine and Arctic plants
§ These plants grow in localities with a high concentration of salts and abundance of water.
§ One of these halophytes only found in the coastal swamps known as MANGROVE vegetation.
§ As a result of the non-availability of water due to the high concentration of salts in the soil, mangrove plants have adapted themselves like the presence of respiratory roots or pneumatophores.
Viviparous types of seed germination and the leaf itself show all the xerophytes characters like its thickness and shining surface.
§ Typical mangrove plants are:-
2. Alpine and Arctic Plants
§ One huge mountains winds velocity is high, strong light (Rich in blue-violet layers) dry air cause excessive transpiration while low temperature (usually below freezing point) and low barometric pressure.
§ High altitude between the range of 8000-9000 feet above sea level.
§ Some plants are also found in Arctic Region.
§ Alpine plants can carry on photosynthesis at low temperature.
§ Due to the high percentage of sugar in their bodies they can endure very low temperature.
§ The Alpine and Arctic plants remain buried under snow of the greater part of the year but who the snow melts away he resume their normal life.
§ Water is a raw material for photosynthesis.
§ Water can absorb relatively large quantity of heat with relatively small change in temperature. Maintain the uniformity of temperature.
§ The intake and loss of water by plants are great concern for the Ecologist.
§ In a given forest area much of the rainfall is interrupted by the crown when it may;
1. drip to the ground
2. flow down the stream
3. be evaporated into the air
4. be absorbed by the leaf surface. e.g.
§ In ponderosa pine in California the average Annual Rainfall is 47″ out this:
i. 84% Reached the forest floor by direct or drip.
ii. 4% Reached the forest floor by stem flow.
iii. 12% Retained by crowns (which is either evaporated or absorbed).
§ The main source of water for terrestrial plants is rainwater.
§ PENCK using precipitation evaporation ration has classified the climate as:-
i. ARID: It is characterized by the condition in which evaporation is greater than precipitation.
ii. Arid-HUMID: When evaporation is more or less equal to precipitation.
iii. HUMID: When evaporation is lesser than precipitation.
§ The distribution of Rainfall over the year is an extremely important limiting factor for all organisms.
§ The mean Annual Rainfall in Pakistan is 2″ – 50″.
§ Depending upon the M.A.R. evenly distributed:-
M. Annual Rainfall
0 – 10″
10″ – 30″
Grasslands, Savana, Open woodland
30″ – 50″
50″ and above
§ Without water no vital activity is possible in the plants and animals.
§ Water effects the inner and outer morphology of the plants organs that together determines the physiognomy of vegetation.
§ The water requirements is generally met by Rainfall, dew, hail, snow.
§ Snow, hail and frost are also harmful to vegetation.
§ The distinction between equatorial forest zones, desert zones near the tropics and temperate forest zones is based upon rainfall.
§ More atmospheric humidity favour growth of Mushrooms, Rusts, Smuts and other parasites of plants.
o THE ATMOSPHERIC FACTORS
· The Earth is enveloped by a gaseous layer called atmosphere.
· It is a reservoir of several elements to life.
· It serves many functions including:-
i. The filtration of Radiant energy coming from the sun.
ii. Insulation from heat at the earth surface.
iii. Stabilization of weather and climate owing to heat capacity of the air.
· Structure of atmosphere: There are five concentric layers within the atmosphere which can be distinguished on the basis of temperature as follows:-
i. The lowest layer of Atmosphere in which man and other living organisms live is called Troposphere
ii. It is about 20 km above the earth surface.
iii. It is a mixture of several gases.
· From the ecological standpoint the term Atmosphere must include:-
1. The thickness gaseous envelope surround our planet.
· The principal gaseous constituents of the atmosphere exist in fairly constant proportions by volume as follows:-
i. Nitrogen = 78%
ii. Oxygen = 21%
iii. Other gases = 1% (Argon, Co2 Neon, Krypton ozone etc).
· The relative percentage of these permanent gases remain almost constant horizontal over the earth and it contains variable amount of:-
(a) Water vapours
(b) Organic and inorganic impurities (pollen grains, micro-organisms, other industrial gases).
(c) Condensed water and ice particles.
· These non-gaseous substances, collectively known as Dust, Pollutants.
· Oxygen and Co2 contents of the air have profound effects upon two important physiological processes of plants i.e. photosynthesis & respiration.
· The gaseous mixture present in the atmosphere is called Air.
· Air moving from high pressure to low atmospheric pressure is called Wind.
· It plays both positive and negative roles in atmosphere.
· Air in motion is called wind.
· It can circulate gases, water vapour and small soil particles.
· The action of wind as an ecological factor maybe direct or indirect.
· In coastal regions or exposed mountain tops, plans lie in danger of being uprooted and blown away by strong wind.
· In coastal region due to continuous and unidirectional wind pressure trees and their branches direct themselves towards the leeward side.
· In strong winds or hurricane, branches of large trees are broken or entire trees are uprooted.
· Violent winds may cause flattening of the herbaceous plants to the grounds, and it take this is called LODGING.
· Mechanically wind can also cause erosion.
· Wind is also important for dispersal of germless i.e. pollen grains, seeds and fruits.
· Indirect effect of wind is physiological which includes the influence on the rate of transpiration of plants.
· Strong wind cause increase in the rate of transpiration and plants fail to mountain an internal water balance and thus suffer from desiccation.
· Under the influence of drying winds generally suffer from dehydration and consequent loss of turgidity and their organs become dwarfed.
o EFFECT OF WIND ON VEGETATION
1. Winds of high velocity are responsible for the uprooting of trees, breaking of branches, twigs etc.
2. Violent wind leads to lodging in crops like wheat, maize, rice, sugarcane etc.
3. Draw ness may result due to strong prevailing winds.
4. Strong winds also cause a considerable degree of soil erosion particularly on open, exposed slopes.
5. High speeds winds lead to more transpiration.
6. In the higher altitude of the Himalayas wind affect the distribution of trees. The tree line or the timberline is lower on windswept slopes.
7. Permanent curvatures may form in plants which are exposed to winds blowing from a particular direction.
8. Sand dunes are the result of wind action.
9. Coastal lands often get salt spray by winds blowing inland from the sea.
10. Wind pollination e.g. Oak, Poplars, Walnut, Conifers, Betula, Alnus, Chir, Acer, Santha, Populus, Salix, Grasses, etc. i.e.
Desiccation, Dwarfing, Deformation, Breakage, Abrasion, Erosion and deposition, Salt spray, wind pollination and wind dissemination by the wind.
o The Following are the important effects of wind on vegetation
1. Wind increases the water loss in plants.
2. Mechanically, wind causes erosion of soil and abrasion of vegetation through the removal of particles.
3. In strong dry and hot winds, young parts of plants may be come shriveled and killed in a few hours and the surface of soil may become dry.
4. In strong winds big are uprooted and small plants also affected.
5. Wind is an important agent for the dispersal of pollen grains, fruits, seeds and spores of the plants.
6. Strong wind causes injuries to plant growing at high altitude.
7. In the desert, the storm results in big sand-dunes which cover the vegetation.
8. In the strong area, the leaves of the plants become small and rolled.
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