Locality factors is defined as:
“The effective climatic, Edaphic, Topographic and Biotic conditions of a site, which influence the vegetation of the locality”.
The flowing are the four broad groups of locality factors:-
- Climatic Factors (related to aerial environment).
- Physiographic factors (Topographic fact).
- Edaphic factors (related to soil condition).
- Biotic factors.
o SOIL/EDAPHIC FACTORS (An Overview)
· Earth is a spherical planet of the solar system. It is differentiated into three main layers:-
· The core is the central portion, the mantle is the middle layer so the earth.
· The crust is the outermost solid zone of the earth which is about 9 to 40 km thick.
The crust is very complex in composition and its surface is covered with the soil which supports rich and highly diversified Biotic communities.
· The soil is one of the most important ecological factors called EDAPHIC FACTORS.
· Soil is defined as: “the unconsolidated top or superficial layer of earth’s crust lying below any aerial vegetation and un-composed dead organic remains and extending down to the limits to which it affects the plants growing its surface. Beneath the soil, lie the subsoil and un-weathered rocks”.
· Edaphic factors are those which are dependent on the soil as such on:-
(A) Soil Texture
(B) Soil Structure
(C) Soil organic matter
(D) Soil organisms
(E) Soil water
(F) Soil Air
(G) Soil Temperature
(H) Soil Cover
(I) Soil Reaction
· Soil at different places varies considerably in their structure, components, and properties. These differences in the soils are often largely responsible for the difference in vegetation within the same climatic region and consequently, they are of great significance in the distribution of plant communities.
· Soil is a stratified mixture of inorganic and organic materials.
· Weathering of rocks is the initial steps of soil forming process which is brought about by:-
i. Physical factors like Temperature, Water, Ice gravity and Wind.
ii. Chemical factors like Solvent action, Hydrolysis, Oxidation, Reduction, Carbonation, and Hydration.
iii. Biological factors. Soil which is formed the products of weathering process is called EMBRYONIC or primary soil.
It may mature into the following types of soils:-
(a) Residual or Sedimentary Soil: This is the mature soil lying immediately over the parent rocks.
(b) Skeletal or Immature Soil: This is only partly weathered material lacking maturation.
(c) Transported or Secondary Soil: The transported soils are those in which the parent materials have been shifted to different places by the Agency of glaciers, Streams and Rivers (ALLUVIAL SOIL) the gravitational forces as landslides (COLLUVIAL SOIL), Wind (AEOLIAN SOIL), Sandstorms (SAND DUNES), Standing Water and wave action (LACUSTRINE SOIL) and oceanic waves (MARINE SOIL).
· The second important process involved in the soil formation includes the addition of organic matter, humification, and mineralization.
· Organic matters are added to the Embryonic soil by various living organisms, plants, and animals living in and on the soil after their death are decomposed and the decomposition product is mixed with the soil.
· All organic plant debris fallow recently to the ground is called LITTER. The litter is composed of dead leaves, twigs, wood, dead roots and various plant products.
· Just below the fresh litter often occurs the material derived from preceding season’s litter in which decay or microbial decomposition has set in this called DUFF.
· The litter is decomposed by soil microbes such as bacteria, actinomycetes, and other fungi. The products of decomposition include various types of inorganic and organic plant nutrients. They are all incorporated into mineral particles which then become dark in color.
The residual finally derived amorphous, incompletely decomposed black colored organic matter added to the mineral matter of the soil is called HUMUS and the process of its formation is referred to as HUMIFICATION.
· Humus includes two types of organic matter:-
§ The partially decomposed matter derived from the litter.
§ Excreta of soil animals like centipedes, millipedes, earthworms, mites, grass-hopper etc. which feed on the litter of plant material.
· Gradually the humus is completely decomposed into simple compounds like carbon dioxide (Co2), Water and Minerals salts by a process called MINERALISATION.
· Depending upon the organic content, soils are generally classified as follows:-
i. MINERAL soil which is rich in mineral particles.
ii. PEAT and MUCH which are rich in organic matter in a wet area.
iii. MORS which is low in basic minerals.
iv. MULLS which are rich in base contents.
· Muller (1879, 1884) has recognized two kinds of Humus:-
§ Mor humus is acidic, abounds in fungi and is low in bacterial content. Mor is deficient in calcium and it develops on sandy soils under conifers.
§ Mull is slightly Alkaline or neutral and abounds in bacteria.
§ Between the two is MODER which has a richer and varied fauna.
The unconsolidated mineral material on the immediate surface of the earth that serves as a natural medium for the growth of land plants.
What is Soil
· Soil may be defined as “The superficial weathered layers of Earth Crust, with which are mixed living organism and products of their decay.”
· Typical a soil is made up of parent material into which there has been incorporated organism matter the spaces remaining between the solid particles are filled with water and gasses.
· Plants are anchored in the soil, which is a source of nutrients for them.
· It also acts as a great reservoir for the water that continuously moves in the soil and absorbed by the plants.
· It also a source of oxygen for the respiration of soil microorganism and the roots of the higher plants.
· Most plants grow best where soil spaces are not exclusively occupied by either water and air.
· Climatic factors, as well as Edaphic factors, are of supreme importance in determining the character of the vegetation over wide areas.
· WARMING (1895) classified plants into various Ecological groups, each of which is characteristics of one type of soils as:
i. Plants found on the acid soil as OXYLOPHYTES
ii. On saline soil as HALOPHYTES
iii. On sand as PSAMMOPHYTES
iv. On rock surface as LITHOPHYTES
v. In rock crevices as CHASMOPHYTES etc.
· PARENT MATERIAL may be defined as: “the unconsolidated, more or less chemically weathered mineral material from which soil is formed”.
· Different types of rocks from which the parent material, in turn, the soil is formed.
i. Igneous Rocks
ii. Sedimentary Rocks
iii. Metamorphic Rocks
o SOIL PROFILE
· Soil profile is the term used for the vertical section of mature soil up to the parental material to show different layers of soil.
· Soils commonly become stratified into layers or Horizons at different depths. The layers of soil at different depth show different compositions and natures. Normally three main horizons or groups of horizons can be recognized.
· These are the upper horizons or A Horizon. The middle horizon or B horizon & C horizon.
· Some recognized an additional horizon called organic or O horizon above the A horizon.
· The important edaphic actors which affect the vegetation are as follows:-
i. Soil Moisture
ii. Soil Reaction
iii. Soil Nutrients
iv. Soil Temperature
v. Soil Aeration or Soil Atmosphere
vi. Biotic components of the soil.
i. Soil Moisture:
Plants absorb a small quantity of Rainwater dew directly but they take a large quantity of water from the soil.
Water held in the soil in the following forms:-
a) Gravitational water
b) Capillary water
c) Hygroscopic water
d) Water Vapour
e) Combined water
· Total water content of the soil is called HOLARD.
· The availability of soil moisture is influenced by many conditions such as:-
(a) Distance of water table from the soil surface;
(b) The rate at which water percolates downward;
(c) The size of soil particles;
(d) The amount of annual Rainfall
(e) The distribution of precipitation throughout the year.
· Soil’s available water is the chief factor responsible for local differences between plant communities.
· Heavily waterlogged soil is injurious for the growing plants because heavy accumulation of water in the soil reduces the soil AERATION.
· Low water content in the soil is also injurious because it causes either temporary or permanent Wilting of plants.
· Soil water is not only important in connection with requirements of plant but it is also the medium by which mineral salts essential in the nutrition enter the plants in dissolved state.
ii. Soil Reaction:
· This edaphic factor influences the growth and distribution of the plants.
· The soil may show acidic, Alluline or Neutral Reactions.
· The accumulation of calcium, sodium and magnesium salts in the soil results in ALKALINITY.
· In the first textbook on plant ecology written by WARMING, in 1895, special emphasis was laid on Edaphic (soil) factor by classifying pants into ecological groups constituted as follows:-
Plants found on acid soil eg. Abies pindrow, Rhododendron, Cranberries.
Plants growing in saline soil e.g. Salsola, Sueda, Tamarix, Atriplex, Salvadora.
Plants growing on sands e.g. Calligorum polygonoides.
Plants growing on rock surface e.g. Lichens & Mosses.
Plants growing in Rock, Crevices e.g. Saxifraga.
· Most of the field crops flourish in slightly Acidic soils e.g. Barley, Maize, Soybeans, Tomato, Rye, Potato.
· Many ferns and beech trees thrive best in slightly Alkaline soils.
· In the acid soils, iron and manganese are available in appreciable quantities, but in the neutral or Alkaline soils they are available in meager quantities to green plants.
iii. Soil Nutrients:
Humus is an important source of mineral and organic nutrients of plants. The fertility of the soil is usually correlated with its humus content.
Humus is the main source of nutrients for soil micro-organisms and green plants.
· Root injury due to low temperature in the winter is more common in sandy soil than in clay.
· Waterlogged soil is deficient in oxygen.
· The germinating seeds respire rapidly and usually they require a large amount of oxygen.
· Earthworms increase the fertility of the soil by adding excretory matters and also making it lose.
· The experiments conducted by British Ecological Society have shown that different soil may affect plants in the following respects:-
1. The ability of seeds to germinate.
2. Size and erectness of plant.
3. The vigor of vegetation organs.
4. The woodiness of the stem.
5. The depth of root system.
6. Susceptibility of plans to drought, frost, and parasites.
7. The number of flowers per plant.
8. Dates of the appearance of flowers.
· Forest soil variously affects the composition of forest stands and ground cover, the rate of trees growth, quality of wood, the vigor of Natural Reproduction, Resistance of stands to diseases.
v PROCESS OF SOIL FORMATION
· Basic material of most soils of small fragments of mineral matter, derived from solid rocks lying beneath the surface of the earth or in some cases they are exposed in the mountain slopes, quarries, canyon, railroad cuttings etc.
· A rock is an aggregation of minerals which are continuously disintegrated into smaller fragments of mineral particles by a process called WEATHERING which includes both physical and chemical weathering.
· Chemical process of weathering consists of Hydrolysis, Carbonation, and hydration.
· Chemical weathering is also promoted by certain species Algae, Bacteria, and lichens that work their way into self-made cavities in rocks by dissolving away the less resistant minerals.
· Physical and chemical disintegration of soil is brought about by Temperature fluctuations, Freezing water abrasive action of particles caused by Running water, moving ice, Gravity, Growing Roots, Rhizoids, Burrowing Animals or man and his animals.
· Depending on the type of parent material soil may be classified as:
(a) RESIDUAL PARENT MATERIAL:-
o It results from the disintegration of Rocks, the intensity of weathering is greatest where rocks minerals are in direct contact with the atmosphere.
(b) TRANSPORTED PARENT MATERIAL:_
o They are composed or derived from their places of origin by various agents.
i. Those brought by gravity or wind are known as COLLUVIAL.
ii. Soil transported by water as ALLUVIAL.
iii. Transported by glaciers as GLACIAL.
iv. Those that are transported by wind as AEOLIAN.
o The weathered rock material forms fine earth, to this added organic matter lichen, higher plants die and their dead parts get mixed up with rock material. To this mixture, remains of materials and their wastes products are also added.
o In Nutshell: Soil texture mainly depends upon physical and chemical of humus and partially decomposed organic matter, results from the contribution of activities of inhabiting plants and animals.
o The plants dependence upon the soil for:-
v S.S. Negi
Ø Soil is made of sand, silt, and clay.
Ø Soil is both acidic and Alkaline in Nature.
Ø This acidity and alkalinity is measured in terms of pH, which is a measure of ionized hydrogen in a liquid system. It is measured on a 0 to 4 point scale as shown below:-
FACTORS AFFECTING DECOMPOSITIONS
The factors which affect the decomposition of soil organic matter are:-
i. Soil moisture and decomposition.
ii. Prevailing Temperature.
iv. C/N Ratio
During the process of decomposition, a steady soil aeration is required. The condition of aeration is as shown below for different types of soils:-
Coarse Sandy Loams
ROLE OF ORGANIC MATTER IN SOILS:-
1. Organic matter is a source of nitrogen in the soil.
Ø Soil organic matter also prevents the further reversion of soluble phosphates.
2. Soil organic matter also helps in the formation of crumbs in the soil.
Ø It acts as a binding agent or cementing material for the formation of crumbs.
Ø This leads to an improvement of soil aeration and the easy movement of water through the soil.
Ø Thus the entire soil is maintained in a good condition and a high level of fertility.
3. WATER HOLDING CAPACITY:- The soil organic matter also serves as an ameliorating agent in sandy soils as well as in the case of clayey soils too. Besides holding a fair quantity of soil moisture by imbibition, humus promotes cohesion in the soil.
4. Coarse organic matter reduces the impact of the falling rainwater and thus prevents accelerated erosion.
5. Helps to promote clods.
6. It is a source of food for soil micro-organisms.
7. It provides chemicals for plant growth.
8. Evaporation from the soil is if not reduced, but at least minimized by the presence of soil organic matter.
9. Organic acids released during the decomposition process, help to reduce the Alkalinity of soils.
EDAPHIC FACTORS: S.S. Negi
Ø Edaphic factors are the Ecological influence brought about by soil
Ø According to WILDE: “A Forest Soil is a portion of the Earth’s surface which serves as a medium for the substance of forest vegetation;
It consists of minerals and organic matter, permeated by varying amounts of water and air ad inhabited by organisms;
It exhibits peculiar characteristics impressed by the physical and chemical action of tree roots and forest debris.”
Ø The following brings out the different aspects of soil formation:
Ø The following factors influence soil formation
ii. Parent Rock
v. Biological agencies
Ø When a pit is dug out in the ground and the soil section examined it is seen that a number of layers having differing characteristics, constitute the soil.
This is the soil profile.
The following horizons are recognized in a soil profile:-
PHYSICAL PROPERTIES OF SOIL
(a) Soil Texture
(b) Soil Structure
(c) Soil Water
(a) Soil Texture
Based on texture a soil may have a coarse texture, medium texture, and fine texture.
Ø The following table shows the composition of various soil types:-
(b) Soil Structure
Ø This is the arrangement of individual soil particles into groups or clusters of definite size and shape.
Ø Soil structure may be as follows:-
Blocky or Nutty
(c) Soil Water
Ø Soil Water or soil moisture is the water present in different forms in the soil.
Ø Available water is the amount of water that can be extracted by plants from a unit of soil.
Ø Hygroscopic water is that water which is retained as a thin film by the soil particles by force more than pf 4.5.
Ø Capillary water is the water retained in the capillary pores of the soil between pf 2.7 to 4.5.
Ø Field capacity is the amount of water that can be retained by the soil against the pull of gravity.
Ø Soil air the combination of gases present in the gaseous phase in the soil.
Ø Soil aeration is the term given to the phenomena by which there is circulation of gases in the soil.
Ø Organic matter includes remains of plants and animals under various stages of decay.
Ø Major nutrients of the soil are nitrogen, phosphorous, potassium, calcium, magnesium, sulfur, carbon etc.
Ø Minor nutrients include Iron, Manganese, Copper, Zinc, Boron, Aluminum, Molybdenum etc.
Ø Nitrogen assimilation is the process of conversion of nitrogen in element form to the organic combination.
Ø Denitrification is the process of breaking down of nitrates into nitrites in the absence of oxygen.
Ø Soil profile is divisible into three distinct horizons i.e. A,B,C.
The upper A horizon or the zone of loss, then B horizon or the zone of deposition are collectively called solum.
However the C zone neither extraction nor accumulation has occurred at all. It is essentially an unaltered zone and is also known as PARENT MATERIAL. The parent rock lying below the parent material is termed as BED ROCK or D Horizon.
The important constituents of the soil are as follows:-
i. Soil texture
ii. Soil structure
iii. Soil organic matter
iv. Soil organisms
v. Soil water
vi. Soil reaction
vii. Soil air
vii. Soil Temperature
ix. Soil Cover
i. Several groups of Bacteria such as Azotobactor, Clostridium, Rhizobium in leguminous roots.
ii. A number of Blue-green Algae are able to liberate nitrogen.
iii. Nitrogen-fixing organisms in the soil are directly responsible for soil fertility.
iv. The larger soil organisms i.e. Insects, Worms, Rodents etc are responsible for considerable mixing and weathering of soil.
v. Earthworms are of special interest as they draw tons of underground soil above the earth’s surface and their movement in the soil they improve soil air.
vi. Rodents i.e. Rabbits, Hares, Mice, Porcupine, Hedgehog etc, being about the great amount of soil to the surface by their burrowing habits.
vii. Plants Roots penetrate the rock crevices, widens the gap and help in breaking the rock apart, thus playing a great role in soil formation.
Ø The temperature of the soil is a factor of vital concern.
Ø The amount of heat that enters the soil is controlled by climate, soil color, altitude and aspect of the land and the vegetation cover.
Ø Generally the mean temperature of the soil is higher than its surrounding atmosphere.
Ø Microclimatological studies of Euphorbia, Acacia, Grewia Community of Karachi University Campus, hawed that at six inches depth, the temperature was 400C while at the soil surface the temperature was 340C.
Rise and fall of soil around the plants due to the abrupt change in temperature are known as HEAVING and THAWING which is injurious to the plant.
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