Describe Energy flow in an Ecosystem ?

The existence of living world depends upon the flow of energy and circulation of materials through the ecosystem. The energy is required the performance of all the life activities. The source of this energy is sun. The solar energy enters the space in the form of light rays. Approximately 57 per-cent of solar energy is absorbed in the atmosphere and scattered in space. About 36 per-cent is expended in heating water and land and in evaporating water. Nearly 8 per-cent of light energy strikes the plants, of which 80-85 per-cent is absorbed, and only fifty per-cent of it is utilized in photosynthesis.

This energy is captured by plants and is stored in the form of potential energy in foodstuffs. These are known as producers and represent first trophic level, in the ecosystem. The energy stored by plants is passed along through the community or ecosystem in a series of steps of eating and being eaten. This is known as food chain. A food chain consists of four steps the primary consumers, secondary consumers and tertiary consumers. Energy flows from the producers to consumers. At each transfer a large proportion (80 to 90 per cent) of potential energy is dissipated as heat produced g the process of respiration and other ways.

There are four successive steps in the production process as follows:

1. Gross primary productivity: It is the total energy stored in the food material synthesized by the green plants or total rate of photosynthesis including to organic matter used up in the respiration during “total photosynthesis or total assimilation.”

2. Net primary productivity : It is the total gross productivity minus energy used up in metabolic process. In other words it is the rate of storage of organic matter in plants in excess of the organic matter utilized in respiration by the plants during the measurement period. This is also called parent photosynthesis or net assimilation.

3. Net community Productivity : It is the rate of storage of organic tatter not used by heterothrophs during the period under consideration, usually the growing season or a year. This is net primary production minus heterotophic consumption.

4. Secondary productivity : The rate of energy storage at consumer levels are referred to as secondary productivity.

Discuss the main kinds of Ecological Succession? Describe the general process of succession?

Types of Ecological Succession

Ecological Succession may be of the following two types:

1. Primary succession : When succession begins on an area which has not been previously occupied by a community (e.g. a new exposed rock area, sand dunes, new islands, deltas, shore or recent lava flow) it is known primary succession. The first group of organisms (plants or animals) which become established in such an area is termed the pioneer community.

2. Secondary Succession : When community development is proceeding  in an area from which a community was removed and where nutrients and conditions for existence are already favourable e.g. cut over bandoned cropland and ploughed field, it is termed secondary sucession.

Secondary succession is usually more rapid because some s are already present. Moreover, previously occupied territory is receptive to community development than the sterile areas.

Depending upon the predominance of green plants or heterotrophic organisms in the initial serval stage, succession is distinguished into autotrophic succession and heterotrophic succession.

  1. Autotrophic succession: it is wide spread in nature and begins in predominantly inorganic environment. It is characterized by early and continued dominance by autotrophic organisms (e.g. green plants).
  2. Heterotrophic succession: It is characterized by early dominance heterotrophs such as fungi, bacteria and animals. It occurs in predominantly lanic environment such as in a stream heavily polluted with sausage, in len log or in small pools receiving leaf bitters in heavy quantities. Energy maximum at the beginning and declines as succession occurs unless .Additional organic matter is imported or an autotrophic community takes place. But in autotrophic succession, energy flow does not usually decline is maintained or increased.

General process of succession

Following steps are found in ground Succession

1. Nudation : Due to human or other natural activities the greenless of rd is called nudation. After nudation the real activity of succession start.

2. Invasion : The seeds collected near the nudation area. The seeds or plants collect first called pioneer. The following steps of invasion are —

(a) Migration: Plant community start at that time when the part of Jamules plants invasion in open area. And the jamules migrate through air, later or animals. Mostly Jamules destroy and those Jamules find according tuation, they raise up and migrate for other places.

(b) Ecesis : After migrate the transfer of new species called Ecesis.

(c) Aggregation : After the colony establish, the seeds become collected. And as a result of it there become start competition for light and place. During competition the strong plants keep alive.

3. Competition and Reaction: Inter specific competition start in plants for light and palace. Strong plants keep alive and start genesis. Plants do action through migration, it is called change in environment. This order is called reaction. Change situation become some little favour towards old plants and more towards new. Thus the new species comes in place of old. Thus the vegetarian plants convert into small and small change into tree.

What do you understand by ecological succession ? Describe various pattern of succession.

Knight (1965) has defined ecological succession as an orderly sequence of different communities over a period of time in some particular area. According to Smith (1966) ecological succession is an orderly and progressive replacement of one community by another till the development of a stable community in that area.

Benton and Warner (1959) have proposed another definition of ecological succession according to which succession is the occurrence of gradual, orderly and predictable changes in the composition of communities towards the climax type.

From the above definitions it can be inferred that the development of community in an ecosystem begins with pioneer stages which are replaced by a series of more mature communities until a relatively stable community is formed which is in equilibrium with the local conditions. The whole series of communities which develop in a given area is called sere, the relatively transitory communities are called seral stages or pioneer stages and the final stabilized community is called the climax community.

Patterns of Succession

Depending upon the types of habitat and varying amount of moisture, the successions are variously designated. The chief patterns are hydrosere or hydrarch (in water), xeroses or xearch (in dry conditions) and mesarch or mesosere (an intermediate type with adequate moisture.

(A) Xerosere — One of the best examples of xerosere is the succession which starts on bare rock, wind blown sand, rocky talus slopes any such place where there is extreme deficiency of water. The various stages in xerosere can be enumerated as follows –

1. Lichen stage : Due to great exposure to sun and extreme deficiency of water, the first pioneers on the bare rock area are a few simple organisms. The most successful of such organisms are crustose lichens. These are able withstand extreme desiccation due to excessive dryness. During rainy
son they absorb large quantities of water and flourish rapidly. Migration to distant rocks takes place either by spores or soredia by wind. The common species of crustose lichens are Rhizocarpon. Rinsodina etc. These begin the slow process of rock disintegration Rock particles and dead organic matter of lichens accumulate to provide conditions possible for the growth of higher forms of lichens.

2. Moss stage: With the accumulation of dust and humus in small entities, the environment is altered enough to allow the establishment of secondary communities in a rather definite sequence. Scattered patches of mosses such as Tortula, Grimmia, Beryum and Barfula etc. begin to invade environment that had so far been dominated by lichens. Later on, mosses ice Funaria, Sphagnum and polytrichnm make their appearance.
Among the animals, mites become more varied ; some small speders md spring tails as well as tardigrades become associated with this secondary community.

3. Herbaceous stage : As the mats of mosses become more extensive more soil accumulates; much of the soil is blown in from surrounding areas during windy periods. More mineral material is added to the soil as acids leach out from the overlying vegetation and increase the depth of the mineral layer. Many annual weeds develop which are, later on, followed by biennial and finally perennial grasses, Andropogon, commonly known as “, sedge, becomes a dominant grass in many areas. With the influx of grasses, the fauna (animals) also becomes varied. Nematodes and larval insects, collembolan, ants and mites appear in the gradually altered environment.

4. Shrub stage : Further modification of the environment provides conditions for the germination and growth of shrubs and perennial woody plants such as Acacia, Prosopis, Capparis, Zizyphus etc.

With the approach of shrubs, the animals also become vivid and numerous and join hands with the vegetation in altering the environment.

5. Climax forest: With the establishment of shrubs, more and more soil is formed and environment becomes increasingly humid. This favours the growth of woody trees. In the beginning trees show stunted growth and are sparsely placed. Finally a climax forest community is established and a number of terrestrial vertebrate make their appearance. The climax community is the last aggregation in the successional series. If the climax conditions do not change and no catastrophic event alters the area, the community maintains itself indefinitely.

(B) Hydrosere : Hydrosere or Hydrarch succession starts in water. A freshly built pond can be taken us a most suitable example of hydrarch succession. The various stages of hydroserecan be enumerated as follows

1. Submerged stage: In initial stages water is poor in nutrients and devoid of life. The pioneers in an aquatic habitat are plankton. The phytoplankton grow floating or suspended in water and multiply. With the death of phytoplankton and zooplankton, the substratum is enriched with organic matter. As water becomes rich in organic and mineral substances, certain rooted submerged hydrophytes make their appearance. Prominent among them are Ceratophyllum, Potamogeton, Vallisneria and Utrioularja etc. By the death and decay of these plants there is further enrichment of the medium. With the increase in nutrients, the level of the pond is raised and it becomes shallow.

2. Floating stage: When the water level in the pond remains only 6 to 8 ft. deep, floating plants begin to appear. These plants include Nymphaea, Nelumbiuni Trapa and Monocharia, etc. These have their roots rooted in the mud and their levels freely floating at the surface. Later on deep floating, plants like Lemna, Azolla and Wolffia grow profusely to cover the water surface.

3. Reed-Swamp stage : As the water body becomes shallow by silting and removal of water by transpiration, the environment becomes less suitable for the free floating and submerged plants. Now reed-swamp plants like Typha, Rumex, and Sagittaria invade the area. The reed swamp plants build up the shores by retaining the sediment and accumulation of plant remains. Beavers, muskrats and other animals carry material into the pond, deciduous vegetation blows in from the shore, and silt is carried in from the surrounding land. Rafts of vegetations from the pond margin drift offshore, strand, and take root, thus establishing islets that grow in size until they meet also and join the shore.

4. March-meadow stage : As the free water is changed to swampy and, the water plants give way to swampy plants such as sedges and rushes. As succession continues, marshy meadow becomes too dry for swampy plants and these are subsequently replaced by herbs and shrubs.

5. Woodland stage : As succession continues, the soil is further built up, so that it becomes drier and is also changed chemically. In time certain mailer species of trees invade the area, taking the place of the shrubs, and eventually full sized forest trees will dominate the scene. At the same time when the vegetation is undergoing these profound changes in the hydrarch succession, the animal life of the community is correspondingly altered. Fish, weavers and muskrats are gradually excluded and land vertebrates make their appearance.

Explain food-chain and food web with suitable examples.

Although biotic and abiotic components are separate by their complex relationship is balanced and functional, which can be explained by following points:

(1) Energy flow, (2) Food chains, (3) Food web

(1) Energy Flow: Existence of organisms depend on energy and main source of energy on the earth is the sunlight. Energy is required by the organisms for their various al activities. We know that two biotic components in the system are autotrophs and heterotrophs. Only green plants are capable to use sun-light r energy source and this energy is transferred from producers to consumers.
During transfer of energy there is loss of some part of energy and energy loss also occurred during respiration.It indicates that energy flow is unidirectional.

In any ecosystem only 1 percent solar energy can be used by green  plants for synthesis of food and such traped energy is responsible for an ecosystem, herbivore obtain energy – from green plants and secondary consumers obtain only 10% energy of a primary consumer (herbivore). At every level energy is lost in similar way. Energy flow and its distribution in the ecosystem is according to the Laws of Themodynamics which are as follows:

(1) First Law: Amount of energy is constant in the world and hence neither energy can be synthesized nor can be destroyed. Energy can be converted from one state to another state. Green plants convert light energy into chemical energy.

(2) Second Law: During energy transfer, some part of energy is lost. This energy loss is diffused in the environment mostly in the form of temperature and remaining is stored in the form of tissues.

Food Chains : The transfer of food energy from the producers through various organisms as they depend for food on one another (herbivore to carnivore to decomposers) with repeated eating and being eaten is known as food chain. In any food chain producers constitute the first trophic level. The energy stored in green plants is used by the herbivores (primary consumers) which constitute the second trophic level. Carnivores (secondary consumers) eat the herbivores and constitute the third trophic level As much, as longer chain, the highest consumer will get less energy because 90% energy is lost during each transfer in the form of temperature etc. are known as food web. Energy flow in a food chain is although unidirectional but through various path in a food web.

As much as complex food web in a ecosystems, the system will be more stable because consumers can obtain their food by various organisms. If there is scarcity of a particular kind of organisms then other organisms may be used as a food in a complex type of a food web. Terrestrial animals have following adaptations

  1. Cursorial adaptations: These adaptations provide ability for fast running. The body is streamlined and digitigrade so they can move through digits. Some are unguligrade for example horse.
  2. Fossorial adaptations : Many animals live in burrows. Body of these animals is Cylindrical e.g. snakes. Tail absent or reduced. Eyes are small and head is blunt.
  3. Desert adaptations : Lives of desert animals depend on water conservation. Some lizards for example moloch has skin capable to absorb moisture and a special structure in the alimentary canal is found in the camel for water storage. Sweat glands are absent in camel.

In Burrowing animals nostrils are on upper side of head to prevent from dust and large scales are present on the head indicate desert adaptation. Colour of desert animals is usually somewhat similar with soil.

  1. Scansorial adaptations : Many animals climb for obtaining food and defense. Lizards have adhesive glands for climbing on the walls. Similarly squirrels, tree frog, monkey etc. are able to run on the trees. These animals have prehensile tail, strong pectoral girdle, semicircular thorax, proximal part of forelimb is long and nailed digits, which are main adaptations.

Food chain : Any one sequence of species through which material and y passes is known as Food-chain. Food chain is a nutritional sequence in an Ecosystem.

Food-web: When number of food-chains are interlocked with each other, they make a very complex structure known as food-web. Food-web exhibits a complex inter-relationship of the populations of plan animals which exists in a particular system.

In other words, “The net work of inter-connected food chains in an ecosystem is called Food-web.”

Food-web exhibits a complex inter-relationship of the populations of plants and animals which exists in a particular ecosystem. In a Food-web each species is dependent upon other and the number of each link species must be sufficient for their continued existence.

What do you mean by Ecology. Explain its Scope, significance and structure of Ecology

The word ecology comes from the Greek Oikos, meaning “household” or “home” or “place of live”. Thus ecology deals with the organism and its place to live. Basically this is the organism’s environment slid so ecology might well be called environmental biology. For one thing the environment includes the surroundings of the animal, and the surroundings can be modified by the animal or plant itself. The environment also includes for the individual organism those of its own kind, as well as organisms of other kinds. There are relationships between individuals within a population and with individuals of different populations. Animals, react in a social sort of way, involving various patterns of behavior. Since all organisms have become adapted to the environment and are always adjusted to the changing environment natural selection and evolution become a part of ecology.

Ecology involves a reciprocal relationship between an organism and s environment. If we consider a pine tree in its natural forest setting, we see that the pine is subjected to environmental influences such as soil water, Wind, soil minerals, the amount of solid oxygen, atmospheric carbon dioxide, the amount of sunlight, the prevailing temperatures, and many other a biotic, or non-living, factors. In addition, there are the biotic, or living, elements of the environment such as bark beetles, birds, squirrels, soil bacteria and fungi, worms and parasites of various types, all of which may be directly or indirectly affect the tree.

The tree, in turn, will modify the surrounding Environment : the shade produced will alter temperatures; its limbs will prevent the free flow of air; transpiration, or water loss, from leaf surfaces will alter the humidity of the air; its root will penetrate the soil, opening up soil channels; and root hairs will extract water from solid spaces, so that the entire soil environment will be modified. We have used a plant to illustrate reciprocal activity. An animal will also exert an influence on the surrounding environment by grazing, predation, burrowing, trampling vegetation and so On. Even the non-living (abiotic) factors of the environment can cause mild or severe changes in an area as evidenced by continuous or abundant precipitation (floods), wind action hurricanes, tornados, typhoons), and gravitational activity (earthquakes, landslides) and so many other factors.

Scope of Ecology : Human being is a part of ecosystem as any other animal. Man has to face many ecological problems like production of grains, livestock, timber, control of pest species, conservation of wildlife etc. Ecology plays very important role in agriculture. Many problems related to agriculture, e.g. management of grasslands, forestry, wood control, crop rotation and biological surveys can be solved using basic concepts of ecology. Other related problems which a man has to face, can be solved through the assistance of trained ecologists. These problems are of varied nature, e.g., pollution, disposal of wastes, deterioration of habitat, knowledge of use of insecticides and fertilizers. Ecologists can also assist in town planning, public health and construction sites for industries. According to Taylor (1936), “Ecology is the sciences of all the relations of all living organisms to all their environment”

Significance of Ecology : It is an important branch of science which helps in understanding the following events:

(1) Interrelationship between living organisms and the environment.
(2) Geographical distribution of organisms.
(3) Interrelationship of populations and community of organisms.
(4) Interrelationship of evolutionary development.
(5) Structural and functional adaptations and ageing of organisms with their physical environment and communities.
(6) Better use of biological productivity of nature for human welfare.
(7) For population control.
(8) Environmental pollution and its control.

From the functional point of view each ecosystem has two main Component

1.Abiotic Component: It consists of nonliving environment which control biotic component. It can be divided into three parts from its structural point of view.

(a) Climatic or physical factors : In physical factors, various environment factors like water, temperature, air, light, rainfall, humidity, energy etc. are included. Number of producers and Consumers in a ecosystem are decided by the environmental factors of the ecosystem and it also decides circulation of nutrients in the system. Energy is transferred by green plants, which are consumed by heterotrophs. Solar energy is Converted into bioenergy by the green plants hence they are referred as autotrophs Amount of abiotic substances in any ecosystem can be referred as standing stage.

(b) Inorganic substance : They comprise essential minerals, for example calcium (Ca), potassium (K), magnesium (Mg), sulphur (S), phosphorus (P) and gases like nitrogen (N2) carbon-dioxide (C02) and Oxygen.

They are taken up by autotrophs producers (green plants) as a raw material and Converted into nutrients. These also participate activity in biogeochemical cycles. These substances are active in both abiotic and biotic components. Initially autotrophs use them and then they reach to heterotrophs through autotrophs. At the time of death of producers or consumers these substances return back into the environment.

(c) Organic Substance : They comprise proteins. Sugar, fats, amino acids etc. Which are synthesized by biotic components of ecosystem and released as wastes or dead remains in the ecosystem. They again enter into the living system through the soil.

2. Biotic components : The living components of the biosphere are called biotic components. The living components of the biosphere are (i) Producers, (ii) Consumers and (iii) Decomposers depending upon their mode of nutrition.

(I) Producers or Autotrophs : Green plants are called producers because they are able to synthesize their food in the presence of sun light and chlorophyll by taking carbon dioxide from the atmosphere and water from the soil. They are also called as autotrophs as they synthesize their own food.  As green plants can convert solar energy into chemical energy of food. So according to E.J.Koromondy they can also be called converter.

(II) Consumers or Heterotrophs : Consumers or heterotrophs are
animals which eat food stuffs manufactured by green Consumers are of three types —
1. Primary Consumers: All the herbivores which feed on producers n plants) are called primary consumers. Some common examples of ary consumers are insects, goats, cows, rabbits, grass Shoppers, deer, rots etc.

  1. Secondary Consumers : The carnivores eat the herbivores or primary consumers and are called secondary consumers. Some common examples of secondary consumers are snakes, frogs, foxes, lizards etc. They are also primary carnivores.
  2. Tertiary Consumers : They are also called secondary carnivores. carnivores eat the secondary consumers and are called as tertiary consumers. Lions and tigers are common examples of tertiary consumers.

Omnivore: An animal which can eat plants as well as flesh of other animals is called omnivore. Man is omnivore.

(iii) Decomposers or Micro consumers or osmotrophs or protrophs : These are the microorganisms which feed on dead bodies of plants and animals and break down complex organic substance into simpler inorganic substances.

What is Ecology ? Explain the main subdivisions of Ecology.

Definition of Ecology : Living organisms are inseparably related with their physical and biological surroundings. This inter-relationship of organisms with their physical and biotic environments is studied under separate discipline of science, which is known as Environmental biology.

Branches of Ecology : The specialized disciplines of ecology are as

Oceanography : It is the study of marine habitat and organisms.
Limonololgy : It is study of freshwater bodies like lakes, ponds

Terrestrial ecology : It is the study of biomes and the organisms d therein. It can further be differentiated into (i) forest ecology,
(ii) cropland ecology and (iii) grassland ecology.

Pedology : It deals with the study of soils, in particular their acidity,  humus-content, mineral contents, soil types etc. and their influence on the plant and animal life.

Community ecology : It is the study of distribution of animals in various habitats.

Animal ecology : It is the interpretation of animal behaviour under natural conditions.

Cytoecology:  It deals with the cytological details in a species in relation to populations in different environmental conditions.

Paleoecology : It deals with the organisms and their environment in geological past.

Insect ecology : It is the ecology of insects.

Mammalian ecology : Ecology of mammals.

Avian ecology : Ecology of birds

Production ecology and Ecological energetics : These branches of ecology deal with the mechanism and quantity of energy conversion and energy flow through different tropic levels in a food chain and rate of increase in organic weight of the organisms in space and time. The productivity is measured both in gross and net values. The total organic production called the gross production, and the actual gain i.e. the gross production minus the loss in respiration is termed as the net production. It includes the proper management of different ecosystems so that the maximum yield can be obtained. This includes agriculture and horticulture.

Applied ecology: The wild life management, range management forest conservation, biological control, animal husbandry, pollution control are the various aspects dealt with in the applied ecology.

Radiation ecology: It deals with the gross effect of radiation and radioactive substances over the environment and living organisms.

Space ecology : It is the modern subdivision of ecology. It is concerned with the development of those ecosystems which support life of man during space flights or during extended exploration of extra terrestrial environments.

Scope of Ecology

Main is as much a part of ecosystem as any other animal. The problems or varied nature, whether socioeconomic, political or similar other policies are all in some way correlated with ecology. For example, production of grains, livestock, timber, fibre, fish, flower, control of pest species, conservation of wild-life etc. are all basically ecological problems. Ecology plays an important role in agriculture. The problems of crop rotation, weed control management of grassland, forestry and biological surveys are nicely solved under ecology. The problems and effects of disposal of wastes, pollution of air, water and land, deterioration of habitat, productivity and contaminant of sea, radioactive pollution, effect of the use of insecticides, herbicides and fertilizers can be taken up only with the assistance of trained ecologists. Ecologists can also assist in town planning. Public health and location industries. TAYLOR (1936), while defining ecology, has nicely pointed out the scope of ecology as “ecology is the science of all the relations of all living organisms to all their environment.

What are the alternative Sources of Energy? Explain conservation of energy ?

Alternative Sources of Energy

Some alternative sources to the fossil fuels are solar energy, hydroelectric energy, geothermal energy, wind power, tidal energy, energy from garbage, dung energy and nuclear energy,

  1. Solar energy : Sun is an inexhaustible and pollution free source of energy. Solar equipment have been developed to harness sun-rays to heat water, cook meals, lit our houses and run certain machines.
  2. Hydro-electric energy: It is produced from the kinetic energy of water falling from height. A number of power stations have been established on many rivers in our country.
  3. Geo-thermal energy : In some places, the heated water comes to the earth’s surface as hot springs. It can be used for heating water and buildings and for generating electricity.
  4. Tidal energy Tidal waves of the sea can be used to generate electricity.
  5. Dung energy : Cattle dung is widely used as fuel in rural areas of our country. This deprives our fields of valuable organic manure. Now cattle dung is used in biogas or gobar gas plant to produce an filmless, low pressure gas. This gas can be used for cooking and heating. The residue is used as manure.
  6. Wind Power : It has been used for centuries to run the wind mills for grinding grains and pump water in certain areas. But the wind does not blow with required intensity all the year round and in all areas. Therefore, wind power can be used in certain areas and on certain days.
  7. Energy from garbage : The garbage of houses contains waste paper, plastics and several other waste materials. It can be used to produced electricity.
  8. Conservation of Energy

The present critical energy position demands an organized efforts at all levels from individual to international action. A considerable amount of energy can be saved by reducing wastage and using energy efficient device. Following measures can help in this effort :

(1) Development of non-conventional energy sources and less dependence on fossil fuels.

(2) Development of technology for the use of solar energy in appliances and transport vehicles.

(3) Improvement of engine and pump designs to increase fuel efficiency.

(4) Planned programme for raising fuel wood, trees and shrubs under the control and maintenance of local communities especially in developing Countries.

(5) Development of efficient and smokeless chulhas or wood stoves.

(6) Effective use of agricultural and animal wastes to obtain biogas and manure.

(7) Development of effective techniques to trap wind and tidal energy.

What is soil erosion? Explain its types and causes ? 

Soil is the upper weathered humus containing part of the earth’s surface. It can sustain terrestrial plant life, this fertile layer of soil is top soil. Soil erosion is removal of top soil from one place to other by the external factors like air and water. In India there is loss of 300-500 lakh tones grains every year due to soil, loss. Three kinds of soil erosions are

 (i) Natural erosion : It occurs in natural conditions. It is not influenced directly or indirectly by man. It is very slow process of soil erosion.

(ii) Fast Soil erosion : It is quick process of erosion in which soil erosion is faster than soil formation, soil loss is greater and animals and man are responsible for fast soil erosion.

(iii) Water Erosion : In water erosion the soil is chiefly eroded by water in three forms, viz.

(1) In sheet erosion, the soil is eroded as a layer from the hill slopes, sometimes slowly and insidiously and sometimes more rapidly. Sheet erosion is more or less universal on : (a) all bare fallow land : (b) all uncultivated land whose plant cover has been thinned out by grazing, fire or other misuse; (c) all sloping cultivated fields and on sloping forest and scrub jungles whose natural porosity of soil has been reduced by heavy grazing, clear felling of trees or burning. Sheet erosion is common in the Himalayan foothills; over the north-eastern parts of the peninsula; in Assam and in the Western and Eastern ghats.

(2) When sheet erosion is allowed to continue unchecked, the silt- laden run-off forms well-defined minute finger-shaped groves over the entire field. Such thin channeling is known as rill erosion. Such type of erosion is active over a wide area in Bihar, U.P., M.P., and in semi-arid areas of Maharashtra, Karnataka, Andhra Pradesh and Tamil Nadu.

(3) In gully erosion, the water forms small rivulets which wash away the soil from bullies. First there is the main ravine and then side checked, goes on extending and ultimately the whole land is converted into a ‘bad land topography’. Gully erosion is more common (a) where the river system has cut down into elevated plateaus so that feeders and branches carve out an Intricate pattern of gullies; and (b) in relatively level Country whenever large blocks of cultivation give rise to concentration of field run-off. The chose of Northern Haryana and Punjab and the bedland of M. P, Rajasthan and U. P., have been formed because of the gully erosion on an extensive scale.

(4) During sudden floods, the fast flowing river undercut the banks I erode the beds. Wherever there is a bend the flowing water gets suddenly and due to increased torsion the Outer bank caves alongside. The eroded material is deposited along the opposite bank nearby. This is known as stream, bank erosion.

Causes of Soil Erosion :

The main factors (causes) of Soil Erosion are as follows :

1. Deforestation : The destruction of forest covers for the supply of Limber and fuel by deliberate human interference leads to increased run-off rain water and its diminished seepage and storage in the soil. The decomposing forest little is no longer replenished by fresh falls of leaves or decaying roots so that plant remains and soil organic matter gradually diminish. The structure of the soil suffers, the run —off increases. It loosens soil and transport it. The water develops power enough to cause devastating floods.

2. Destruction and Overgrazing of Pastures : A properly manage, lightly grazed pasture might form a permanent protection to the soil because it provides an efficient cover for preventing erosion and reducing run-off in much as it covers the surface of the ground protecting it from the direct impact of the falling rain drops and thus keeping the pores of the soil open and capable of receiving excessive amounts of water. But when there is over-grazing by cattle, goats and sheep, the soil becomes uncovered as the grass over-gazed becomes worn and thin, rain drops begin to fall directly on the soil puddling the surface and clogging up the pores with mud. Infiltration into the soil is reduced and the fun-off of the water increases. All this .invariably leads to a deterioration in botanical composition and an Increase In the growth of weeds as well as to an increase in the area of bare ground.

3. Shifting Cultivation : Man’s furthless destruction of the forest for shifting cultivation has also decreased the area under forest. Shifting or Jhuming cultivation is chiefly practiced by the primitive tribes for raising food for them. According to this system of farming a patch of forest is selected. Its trees and bushes are then cut and burnt down on the ground in order to clear room for a field. The ground is, then, lightly ploughed and the seed is sown broadcast and raked into the soil, at the first fall of the rains which is immensely fertile owing to the wood ashes and accumulated humus.

4. Economic and Social Factors : Certain economic factors arising out of the traditional outlook, social economy and economic structure of the community have also indirect bearing on the soil erosion. Of these, the system of farming, size of the farm tenancy, tenant-landlord relationship are too significant facts to be over looked. Bad agricultural practices also lead to I the loss of top fertile soil.

5. Nature of Crop Grown : In arable agriculture, crops vary widely in their effect on erosion losses While barely, oats and wheat have “low Units of index” of soil loss; corn, sorghum, cotton, soyabean have “higher units of index.”