India has the most variable natural ecosystems as in India, one side's climate and environmental conditions are totally different from another side. Somewhere it is dessert here India and somewhere Ice falls here. India has 2.4% part of world's area. But it holds over 8% of the world's total diversity. India has three major ecosystems :-
(1)    Terrestrial Ecosystem
(2)    Wetlands
(3)    Aquatic Ecosystem

5.1.    Terrestrial Ecosystem
A terrestrial ecosystem is an ecosystem found only on land forms. So it includes 100% of Earth's surface. The major terrestrial ecosystems of India are :-
5.1.1.    Grassland Ecosystem (Tall grass Prairies) : The inclusive ecosystem of plants, animals and microorganisms in grass vegetation is termed as grassland ecosystem.
eg.   -    Prairies of western North America.
        -    The pampas of Argentina
        -    The Russian stapes.
        -    Veldts of South Africa
        -    Pusztas of Hungary.
        -    Tussocks of New Zealand.
        -    The steppes of Asia.
Grazing animals like elk, bison, wolves, prairie dogs, foxes, ferrets, birds of prey grouse, reptiles and insect prairies dogs, a ground squirrel-like rodent considered to be a keystone species.
Savannah: Savannah is one of the popular grassland woodland ecosystems. The trees do not make the canopy. They allow light to reach the ground to support grasses. These are called tropical grassland also Savanna has widely scattered trees or clumps of trees.
Distribution areas of Savanna are South American Savannah, South American tropical forests, Guinean Savannah. Savannah covers 20% of Earth's land area. Seasonal water availability has been found in the Savannah with the majority of rainfall confined to one season. Savannah is associated with several types of biomes and frequently in a transitional zone between forest and grassland.
5.1.2.    Forest Ecosystem: India is among the 10 top most countries in the world, covering a little over 78 million hectares/23.8% of the country's geographical area by forests. The following types of vegetation and distributions are found in India:-    Tropical Rain Forests: Tropical rain forests can be defined in two words: hot and wet. Means monthly temperatures exceed 18°C (64°f) during all months of years. Average rainfall can exceed 1000 cms. Tropical rain forests exhibit high levels of biodiversity. Tropical rain forests have been called the "world's largest pharmacy" as over one-quarter of natural medicines have been discovered here. Tropical Rain forests are called as lowland equatorial evergreen rainforest.
eg. : Northeastern India, Western slopes of the western ghats, foot-hills of the Himalayas and in the Andaman and Nicobar Islands.
The common trees of these forests are Ablus, Mahogany, Ebony, rosewood, Sirhan (Dalbergia sissoo), Sandalwood (Santalum album). Trees are tall (up to 60 meters) and form a dense canopy overhead.    Tropical Deciduous Forest: They are termed as Monsoon forests also, as these forests are dominated by trees that lose their leaves each year. Warmth, Moist summers and mild winter all are involved in these forests. They are important from the economic point of view. They are subdivided into two types:-
(i)    Moist Deciduous Forests
(ii)    Dry Deciduous Forests
Trees of these forests are teak (Tectona Gradis), sal (Shorea robusta), sandalwood (Santalum album), Shisham (Dalbergia sissoo), Hurra (Terminalia chebula), Khair (Acacia catechu), Bamboo and Cane. These forests are confined to north-eastern India, eastern slopes of the Western Ghats, the Eastern Ghats, Chhota Nagpur Plateau, Orissa, Chhattisgarh and Madhya Pradesh, hills of east Rajasthan, Western Madhya Pradesh and parts of central Deccan Plateau.    The Thorn and Shrub Forests: These includes the xeric shrubland ecoregion of India, southernmost Sri Lanka, Punjab Plains in North, Rajasthan, U.P., M.P., Haryana and few parts of south India.
Trees are kikar, Babul, Khair, Acacia, Munj and Sawai grass present in these forests. Rainfall is less than 50 cms here. These forests consist of open woodland with thorny trees with short trunks, spiny and xerophytic shrubs and dry grassland. These are the habitat of "great India bustard" and blackbuck.    Tidal Forests: These forests are called as mangrove forests. Mangroves are shrubs or small trees that grow in coastal saline and brackish water. Mangroves are mainly located between latitude 25°N and 25°S. The best example of mangrove (Tidal forest) is "Sundarbans". Sundarban is a well-known mangrove forest covering the Ganga-Brahmaputra delta in West Bengal. Due to common tree "Sundari", it was given the name Sundarbans.    Mountain Forest: The Himalayas & Ghats are confined in these forests. These are the regions which include lands in a scattered form. A large range of plants and animals are found in these forests.
Sals, Qaks, chestnuts, Apples, pine, Cedar, Spruce, silver fir, birches and junipers. Tropical or Temperate forests, Savannah, Scrubland, desert or tundra are the continent of mountain forest.    Desert : Desert is also known as the Great Indian Desert. It's a large arid region in the northwestern part of India. It forms a natural boundary between India and Pakistan. Desert lacks vegetation. Rainfall is usually less than 25 cm/year. Temperature gets extreme here whether it is cold or hot. Rajasthan, Haryana, Punjab and Gujarat states are included in the desert area of India. The soil of the desert remains dry as water is vaporized due to the extreme temperature at the day time. Exotic trees like Eucalyptus, Acacia, Cassia and other genera is present in the desert.    Tundra (Arctic Tundra) : Tundra is a type of biome where the tree grows for a short season and maintained by low temperature vegetation like shrubs, mosses, lichens and sedges are included in the Tundra region. The Ecotone between the tundra and forest is known as the tree line or timberline. There are three types of tundra 
(1)    Arctic Tundra        (2)    Alpine Tundra        (3)    Antarctic Tundra
(1)    Arctic Tundra : Arctic tundra involves in the last Northern Hemisphere. The soil of Arctic tundra is in frozen form from 25-90 cm. So, plants are found negligible here But animals like Lemmings, Voles, Weasles, Arctic foxes, Snowshoe hare, Ptarmigan, snowy owls and musk oxen etc. In Bare or rocky area, some mosses or any low growing plant can live or survive only. Otherwise it's impossible to grow in the frozen soil for any other plants.
(2)    Alpine Tundra : Alpine tundra occurs in mountains in all over the world. The flora of Alpine Tundra are shrubs that are too dwarf close to the ground. Climate of Alpine tundra is like polar areas i.e. very low. Alpine soils are better drained than Arctic. Alpine tundra transitions to subalpine forests below the tree line, stunted forests occurring at the forest-tundra ecotone are known as "Krummholz". The environment of tundra have permafrost-water permanently frozen in the soil-while liquid water is present for only short periods of year.
(3)    Antarctic Tundra: This occurs in Antarctica and on several Antarctic and Subantarctic Islands, including the south. Georgia and the South Sandwich Islands and the Kerguelen Islands. Too cold and Dry weather is seen in this type of Tundra forest. Most of the region of Antarctic tundra is covered by ice. Somewhere if soil is rocky, than only it supports lichens. Mosses, liverworts, aquatic algae, terrestrial Algae species, Antarctic hair grass (Deschampsia Antarctica) and Antarctic pearlwort (Colobanthus quietness) are the other floras present in this region.    Boreal forests (Taiga): Taiga or Boreal forests are only found in the Northern hemisphere of Earth, mainly latitudes 50° and 60° N. Taiga are located in the south of the tundra. These forests form an almost continuous belt around the Earth, Sandwiched between temperate deciduous forests to the south and tundra to the north. Temperature remains low in the taiga but moisture tends to stick around for the longer period of time due to low the temperatures and evaporation rates. Large mammals like moose, bears and wolves are found here.    Chaparrals - Forest Ecosystem (Meditarian shrublands): Chaparrals are shrublands found mainly in the California state of USA. It covers 5% part of California and associated Mediterranean shrubland an additional 3.5%. Plants of chaparrals are highly flammable. Chaparrals are characterized by infrequent fires, with intervals of approximately 5-10 years to over a hundred years. Plants grow as woody shrubs with hard small leaves and are drought-tolerant.
5.2.    Wetlands
These are the land area that is saturated with water, either it can be permanently or seasonally. The plants of wetlands are seagrasses, eelgrass, lilies, lily pad, duckweed, Typha, pettandra virginica and cypress. The fauna of wetlands includes fishes, shellfishes, frogs, alligators, crocodiles snakes, lizards, turtles, platypus, panthers and lower animals. 

Hence wetlands have a very rich biodiversity coral reefs, brackish lakes, Riverine flood plains, Inland deltas, shrub swamps on inorganic soils, Peatlands, Rock pools, freshwater springs, salt pans, sewage farms, irrigated channels, seasonally flooded areas, all these are included in wetlands.  
5.3.    Aquatic Ecosystem
The aquatic ecosystem is an ecosystem which is consisted of water bodies like ocean water, fresh water, estuarine ecosystems. Wetlands are also included in the Aquatic system. Aquatic Ecosystem can be subdivided into two categories:-
(i)    Ocean/Marine Water Ecosystem
(ii)    Fresh Water Ecosystem

5.3.1.    Ocean/Marine Water Ecosystem: It covers 71% of Earth's surface, contains 97% water of the planet, generates 32% of net primary production of the world. This ecosystem is distinguished by the presence of dissolved compounds, especially salts in water. Other dissolving compounds can be sodium (Na) and chlorine (cl). Marine water ecosystem can be divided into many zones according to their depth and shoreline features:-
(a)    Oceanic zone: It is a vast open part of the ocean where animals live eg. whales, sharks, tuna etc.
(b)    Benthic Zone: This zone includes the zone where invertebrates live.
(c)    Intertidal Zone: It is the area between High and low tides. It is termed as littoral zone. It includes shallow water.
5.3.2.    Fresh Water Ecosystem: It covers approximately 0.78% of Earth's surface and inhabit 0.09% of its total water and generates 3% of its net primary production. It contains 41% of fishes in the world. The basic type of freshwater ecosystem is -
(a)    Lentic         (b)    Lotic    Lentic Ecosystem: It includes slow-moving water, including pools, lakes and ponds. Lentic ecosystems or lake ecosystem can be divided into three zones.

(A)    Littoral zone/Pelagic Zone
(B)    Limnetic Zone/Photic Zone
(C)    Profundal Zone/Aphotic Zone
(A)    Littoral Zone: Littoral zone is a shallow zone near the shore wetland plants are rooted in this zone light of sun reaches the bottom of this zone. So this zone takes a maximum amount of sunlight.
(B)    Limnetic/Photic Zone: It is an open water zone, where sunlight supports photosynthesis for Algae and the species who live there, feed upon algae.
(C)    Profundal/Aphotic Zone: It is a close water zone, where sunlight does not reach, and species are mostly dependent on detritus material coming from littoral and photic zone.    Lotic Ecosystem: It includes fast-moving water. eg.-Waterfalls, flowing rivers etc. Fast moving water contains a greater concentration of dissolved oxygen, so it results from a greater diversity of species here Algae and Anadromous fishes are the main food base of living species here.

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