6 - 8 Grassland Ecosystem; Desert Ecosystem; Aquatic Ecosystem UPSC Notes | EduRev

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6. GRASSLAND ECOSYSTEM

Found where rainfall is about 25-75 cm per year, not enough to support a forest, but more than that of a true desert. Vegetation formations that are generally found in temperate climates.

In India, they are found mainly in the high Himalayas. The rest of India's grasslands are mainly composed of steppes and savannahs.

Steppe formations occupy large areas of sandy and saline soil; in western Rajasthan, where the climate is semi-arid,

The major difference between steppes and savannahs is that all the forage in the steppe is provided only during the brief wet season whereas in the savannahs forage is largely from grasses that not only grow during the wet season but also from the smaller amount of regrowth in the dry season.

 

Types of Grasslands 

1. Semi-arid zone (The Sehima-dichanthium type)

It covers the northern portion of Gujarat, Rajasthan (excluding Aravallis), western Uttar Pradesh, Delhi and Punjab.

The topography is broken up by hill spurs and sand dunes.

Senegal, Calotropis gigantic, Cassia articulate, Prosopis cineraria, Salvador oloides and Sisyphus Nummularia which make the savannah rangeland look like scrub.

2. Dry sub humid zone (The Dichanthium- cenchrus-lasitrrus type)

It covers the whole of peninsular India (except Nilgiri).

The thorny bushes are Acacia catechu, Mimosa, Sisyphus (bear) and sometimes fleshy Euphorbia, along with low trees of Anogeissus latifolia, Soymida febrifugal and other deciduous species. 

Sehima (grass) is more prevalent on gravel and the cover maybe 27%. Dichanthium (grass) flourishes on level soils and may cover 80% of the ground.

3)  Moist sub humid zone (The Phragmities- sacchrum-imperata type)

It covers the Ganga alluvial plain in Northern India.

The topography is level, low lying and ill-drained.

Bothriochloa pertusa, Cypodon dactyl on and     Dichanthium annulated are found in transition zones.

The common trees and shrubs are Acacia Arabica, hogeissus, latifolia, Butea monospermous,

Phoenic sylvestris and Zizyphus nummularia. 

Some of these are replaced by Borassus sp in the palm savannahs especially near Sunderbans.

4) The Themeda - Arundinella type

This extends to the humid montane regions and moist sub-humid areas of Assam, Manipur, West Bengal, Uttar Pradesh, Punjab, Himachal Pradesh and. Jammu and Kashmir.

The savannah is derived from the humid forests on account of shifting cultivation and sheep grazing.

Indian Grasslands and Fodder Research Institute, Jhansi and Central Arid Zone Research institute, Jodhpur

 

Role of fire 

Fire plays, an important role in the management of grasslands.

Under moist conditions fire favours grass over trees, whereas in dry conditions fire is often necessary to maintain grasslands against the invasion of desert shrubs.

Burning increases the forage yields, e.g. Cynodon daotylon

 

7. DESERT ECOSYSTEM

Deserts are formed in regions with less than 25 cm of annual rainfall, .or sometimes in hot regions where there is more rainfall, but unevenly distributed in the annual cycle.

Lack' of rain in the mid latitude is often due to stable high pressure zones; deserts in temperate regions often lie in "rain shadows", that is where high mountains block off moisture from the seas. 

The climate: of these biomes is modified by altitude and latitude. At greater distance from the equator the deserts are cold and hot near equator and tropics.

As the large volume of water passes through the irrigation system, salts may be left behind that will gradually accumulate over the years until they become limiting, unless means of avoiding this difficulty are devised

Adaptations 

(i)  These plants conserve water by following methods:

They are mostly shrubs. Leaves are absent or reduced in size. 

Leaves and stem are succulent and water storing. 

In some plants even the stem contains chlorophyll for photosynthesis.

Root system is well developed and spread over large area. 

The annuals wherever present germinate, bloom and reproduce only during the short rainy season, and not in summer and winter.

(ii) The animals are physiologically and behaviourally adapted to desert conditions. 

They are fast runners.

They are nocturnal in habit to avoid the sun's heat during day time.

They conserve water by excreting concentrated urine.

Animals and birds usually have long legs to keep the body away from the hot ground.

Lizards are mostly insectivorous and can live without drinking water for several days. 

Herbivorous animals get sufficient water from the seeds which they eat.

Mammals as a group are poorly adapted to deserts

 

Indian Desert — Thar desert (hot) 

The climate of this region is characterised by excessive drought, the rainfall being scanty and, irregular.

The winter rains of northern India rarely penetrate into the region.

The proper desert plants may be divided into two main groups.

i)  Depending directly upon on rain and 

ii) Those depending on the presence of subterranean water.

The first group consists of two types:  

The 'ephemera's' and the rain perennials'. 

The ephemera's are delicate annuals, apparently free from any xerophilous adaptations, having slender stems and root-systems and often large Flowers. 

They appear almost immediately after rain, develop flowers and fruits in an incredibly short   time, and die as soon as the surface layer of the soil dries up.

The rain perennials are visible above the ground only during the rainy season, but have a perennial underground stem.

The second group - depending on the presence of subterranean water

By far the largest number of indigenous plants are capable of absorbing water from deep below the surface of the ground by means of a well-developed root system, the main part of which generally consists of a slender, woody tap root of extraordinary length.

Generally, various other xerophilous adaptations are resorted to such as reduced leaves, thick hairy growth, succulence, coatings of wax, thick cuticle, protected stomata, etc., all having for their object of reduction of transpiration.

       

Fauna 

It is home to some of India's most magnificent grasslands and sanctuary for a charismatic bird, the Great Indian Bustard. Among the mammal fauna, the blackbuck, wild ass, chinkara, caracal, Sand grouse and desert fox inhabit the open plains, grasslands, and saline depressions.

The nesting ground of Flamingos and the only known population of Asiatic wild Ass lies in the remote part of Great Rearm, Gujarat.

It is the migration flyway used by cranes and flamingos.

Some endemic flora species of Thar Desert includes Calligonum Polygonoides, Prosopis cineraria, Tecomella undulate, Cenchrus biflorus and Sueda fruticosa , etc.

 

Cold Desert/ Temperate Desert 

Cold desert of India include areas of ladak, leh and kargil of kashmir and spiti valley of Himachal Pradesh and some parts of northern Uttaranchal and Sikkim. Lies in rain shadow of Himalaya Oak, pine, deodar, birch and rhododendron are the important trees and bushes found there. Major animal include yaks, dwarf cows, and goats.

Severe arid conditions - Dry Atmosphere

Mean annual rainfall less than 400mm

Soil type - sandy to sandy loam, Soil pH - neutral to slight alkaline. 

Soil nutrient - Poor organic matter content, low water retention capacity 

Bio-diversity

Cold desert is the home of highly adaptive, rare endangered fauna, such as:

Asiatic Ibex, Tibetan Argali, Ladakh Uriyal, Bharal, Tibetan Antelope (chiru), Tibetan Gazelle, Wild Yak, Snow Leopard, Brown Bear, Tibetan Wolf, Wild Dog and Tibetan Wild Ass ('Kiang' a close relative of the Indian wild ass), Woolly hare, Black Necked Crane, etc.

India as a signatory to United Nations Convention to Combat Desertification (UNCCD) has submitted four National Reports to UNCCD

In the years 2000, 2002, 2006 and 2010 Some of the major programmes currently implemented that address issues related to land degradation and desertification is:-

  1. Integrated Watershed Management Programme (IWMP),
  2. National Afforestation Programme (NAP),
  3. National Mission for Green India (GIM),
  4. The Mahatma Gandhi National Rural Employment Guarantee Scheme
  5. (MGNREGS), 
  6. Soil Conservation in the Catchment of River Valley Project and Flood Prone River,
  7. National Watershed Development Project for Rainfed Areas (NWDPRA),
  8. Desert Development Programme (DDP) 
  9. Fodder and Feed Development Scheme-component of Grassland Development including 
  10. Grass Reserves, Command Area Development and  Water Management (CADWM)  programme etc

 

8. AQUATIC ECOSYSTEM

Fresh water ecosystems- The salt content of fresh bodies is very low, always less than 5 ppt (parts per thousand). E.g. lakes, ponds, pools, springs, streams, and rivers

Marine ecosystems - the water bodies containing salt concentration equal to or above that of sea water (i.e., 35 ppt or above). E.g. shallow seas and open ocean

Brackish water ecosystems- these water bodies have salt content in between 5 to 35 ppt. e.g. estuaries, salt marshes, mangrove swamps and forests.

 

AQUATIC ORGANISMS 

The aquatic organisms are classified on the basis Of their one of occurrence and their ability to cross these zones. Can be classified on the basis of their life form or location into five groups

1. Neuston:

These are unattached organisms which live at the air-water interface such as floating plants, etc.

Some organisms spend most of their lives on top of the air-water interface such as water striders, while others spend most of their time just beneath the air-water interface and obtain most of their food within the water. E.g., beetles and back-swimmers.

2. Periphyton:

These are organisms which remain attached to stems and leaves of rooted plants or substances emerging above the bottom mud such as sessile algae and their associated group of animals.

3. Plankton

This group includes both microscopic plants like algae (phytoplankton) and Animals like crustaceans and protozoans (zooplankton) found in all aquatic ecosysteins, except certain swift moving waters

The locomotors power of the planktons is limited so that their distribution is Controlled, largely, by currents in the aquatic ecosystems.

4. Nekton:

This group contains animals which are swimmers. The nektons are relatively large and powerful as they have to overcome the water currents. 

5. Benthos:

The benthic organisms are those found living in the bottom of the water mass.

Practically every aquatic ecosystem contains well developed benthos

Factors Limiting the Productivity of Aquatic Habitats 

1. Sunlight:

Sunlight penetration rapidly diminishes as it passes down the column of water.

The depth to which light penetrates a lake determines the extent of plant distribution.

Based on light penetration and plant distribution they are classified as photic and aphotic zones

Photic zone:

It is the upper layer of the aquatic ecosystems, up to which light penetrates and within which photosynthetic activity is confined.

The depth of this zone depends on the transparency of water.

Photic (or. “Euphotic") zone is the lighted and usually well-mixed portion that extends from the lake surface down to where the light level is 1% of that at the surface.

Aphotic zone:

The lower layers of the aquatic ecosystems, where light penetration and plant growth are restricted forms the aphotic zone. 

Only respiration activity takes place. (Photic-both respiration and photosynthesis take place)

Aphotic zone is positioned below the littoral and photic zones to bottom of the lake where light levels are too low for photosynthesis. 

This deep, unlit region is also known as the profounder zone.

Dissolved oxygen:

Oxygen enters the aquatic ecosystem through the air water interface and by the photosynthetic. Average concentration of dissolved oxygen as 10 parts per million by weight.

Dissolved oxygen escapes the water body through air-water interface and through respiration of organisms (fish, decomposers, zooplanktons, etc.)

The amount of dissolved oxygen retained in water is also influenced by temperature.

Other limiting factors which influence on aquatic productivity are

Transparency:

Transparency affects the extent of light penetration.

Suspended particulate matters such as clay, silt, phytoplankton, etc. make the water turbidity. Consequently it limits the extent of light penetration and the photosynthetic activity in a significant way.

Temperature:

The water temperature changes less rapidly than the temperature of air because water has a considerably higher specific heat than air.

Since water temperatures are less subject to change, the aquatic organisms have narrow temperature tolerance limit.

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