Shankar IAS Summary: Terrestrial Ecosystem- 1 | Environment for UPSC CSE PDF Download

Terrestrial Ecosystem

The type of ecosystems which are predominantly found on land are called the terrestrial ecosystems. Terrestrial ecosystems cover approximately 140 to 150 million km², which is about 25 to 30 percent of the total earth surface area. 

• The interrelations between organisms and the environment on the land constitute "Terrestrial Ecology". 
• The most important limiting factors of terrestrial ecosystems are moisture and temperature.
• There are different types of terrestrial ecosystems, which are widely distributed around the geological zones. They include: 

1. Tundra
2. Forest Ecosystem
3. Grassland Ecosystem
4. Desert Ecosystem

1. Tundra

The word tundra means a "barren land" since they are found where environmental conditions are very severe.

There are two types of tundra:

1. Arctic
2. Alpine
   Arctic tundra (in blue) and Alpine tundra (in grey)

Distribution of Arctic & Alpine Tundra

• Arctic tundra extends as a continuous belt below the polar ice cap and above the tree line in the northern hemisphere. It occupies the northern fringe of Canada, Alaska, European Russia, Siberia, and the island group of the Arctic Ocean.
• On the south pole, tundra is very small since most of it is covered by the ocean. Alpine tundra occurs at high mountains above the tree line. Since mountains are found at all latitudes therefore alpine tundra shows day and night temperature variations.

Flora and Fauna of Arctic & Alpine Tundra

• Typical vegetation of arctic tundra is cotton, grass, sedges, dwarf heath, willows, birches, and lichens. Animals of tundra are reindeer, musk ox, arctic hare, caribous, lemmings, and squirrel.
• They are protected from chillness by the presence of thick cuticle and epidermal hair. Mammals of the tundra region have large body sizes and small tail and ear to avoid the loss of heat from the surface. The body is covered with fur for insulation.

2. Forest Ecosystem

A forest ecosystem is a functional unit or a system which comprises of soil, trees, insects, animals, birds, and man as its interacting units. A forest is a large and complex ecosystem and hence has greater species diversity

• Includes a complex assemblage of different kinds of biotic communities. Optimum conditions such as temperature and ground moisture are responsible for the establishment of forest communities.
• Forests may be evergreen or deciduous. Distinguished on the basis of the leaf into broad-leafed or needle-leafed coniferous forests in the case of temperate areas are
  Classified into three major categories: 
  (i) Coniferous forest
  (ii) Temperate forest
  (iii) Tropical forest

Types & Characteristics of Forests

Coniferous Forest (Boreal Forest)

• Cold regions with high rainfall, strong seasonal climates with long winters and short summers evergreen plant species such as spruce, fir and pine trees, etc. and by animals such as the lynx, wolf, bear, red fox, porcupine, squirrel, and amphibians like Hyla, Rana, etc.

Conifers are a group of trees and Shrubs that produce Cones

• Boreal forest soils are characterized by thin podzols and are rather poor. Both because the weathering of rocks proceeds slowly in cold environments and because the litter derived from conifer needle (leaf is decomposed very slowly and is not rich in nutrients).
• These soils are acidic and are mineral deficient. This is due to the movement of a large amount of water through the soil, without a significant counter-upward movement of evaporation, essential soluble nutrients like calcium, nitrogen, and potassium are sometimes leached beyond the reach of roots.
• This process leaves no alkaline-oriented cations to encounter the organic acids of the accumulating litter. The productivity and community stability of a boreal forest are lower than those of any other forest ecosystem.

Temperate Deciduous Forest

• The temperate forests are characterized by a moderate climate and broad-leafed deciduous trees, which shed their leaves in fall, are bare over winter, and grow new foliage in the spring.
• The precipitation is fairly uniform throughout. Soils of temperate forests are podzolic and fairly deep.

Temperate Evergreen Forest 

• Parts of the world that have the Mediterranean type of Climate are characterized by warm, dry summers and cool, moist winters. 

Trees and Their Leaves: Broad Leafed Evergreen Trees are shown in the upper right-hand corner of the image.

• Low broad-leafed evergreen trees. Fire is an important hazardous factor in this ecosystem and the adaptation of the plants enables them to regenerate quickly after being burnt.

Temperate Rain Forests

• Seasonality with regard to temperature and rainfall.
• Rainfall is high, and fog may be very heavy. It is an important source of water rather than rainfall itself. 
• The biotic diversity of temperate rain forests is high as compared to other temperate forest. The diversity of plants and animals is much lower than compared to the tropical rainforest. 

Tropical Rain Forests 

• Near the equator.
• Among the most diverse and rich communities on the earth. Both temperature and humidity remain high and more or less uniform. The annual rainfall exceeds 200 cm and is generally distributed throughout the year. 
• The flora is highly diversified. The extremely dense vegetation of the tropical rain forests remains vertically stratified with tall trees often covered with vines, creepers, lianas, epiphytic orchids, and bromeliads. 
• The lowest layer is an understory of trees, shrubs, herbs, like ferns and palms. The soil of tropical rainforests are red latosols, and they are very thick.

Tropical Seasonal Forests 

• Also known as monsoon forest occur in regions where total annual rainfall is very high but segregated into pronounced wet and dry periods. 
• This kind of forest is found in South East Asia, central and south America, northern Australia, western Africa and tropical islands of the Pacific as well as in India.

Subtropical Rain Forests

• Broad-leaved evergreen subtropical rain forests are found in regions of fairly high rainfall but less temperature differences between winter and summer.
• Epiphytes are common here.
• Animal life of the subtropical forest is very similar to that of tropical rainforests.

Indian Forest Types

Forest types in India are classified by Champion and Seth into sixteen types.

(a) Tropical Wet Evergreen Forests

• Are found along the Western Ghats, the Nicobar and Andaman Islands, and all along the northeastern region.
• It is characterized by tall, straight evergreen trees. The trees in this forest form a tiered pattern: Beautiful fern of various colours and different varieties of orchids grow on the trunks of the trees.

(b) Tropical Semi-Evergreen Forests

• Found in the Western Ghats, Andaman and Nicobar Islands, and the Eastern Himalayas. Such forests have a mixture of wet evergreen trees and moist deciduous trees. The forest is dense.

(c) Tropical Moist Deciduous Forests

• Found throughout India except in the western and the northwestern regions.
• The trees are tall, have broad trunks, branching trunks, and roots to hold them firmly to the ground. These forests are dominated by sal and teak, along with mango, bamboo, and rosewood.

(d) Littoral and Swamp

• Found along the Andaman and Nicobar Islands and the delta area of the Ganga and the Brahmaputra.
• They have roots that consist of soft tissue so that the plant can breathe in the water.

(e) Tropical Dry Deciduous Forest

• The northern part of the country except in the North-East. It is also found in Madhya Pradesh, Gujarat, Andhra Pradesh, Karnataka, and Tamil Nadu. The canopy of the trees does not normally exceed 25 metres.
• The common trees are the sal, a variety of acacia, and bamboo.

(f) Tropical Thorn Forests

• This type is found in areas with black soil- North, West, Central, and South India. The trees do not grow beyond 10 metres. Spurge, caper, and cactus are typical of this region.

(g) Tropical Dry Evergreen Forest

• Dry evergreens are found along with Tamil Nadu Andhra Pradesh and the Karnataka coast. It is mainly hard-leaved evergreen trees with fragrant flowers, along with a few deciduous trees.

(h) Sub-tropical Broad-leaved forests

• Broad-leaved forests are found in the Eastern Himalayas and the Western Ghats, along the Silent Valley. There is a marked difference in the form of vegetation in the two areas.
• In the Silent Valley, the poonspar, cinnamon, rhododendron, and fragrant grass are predominant. In the Eastern Himalayas, the flora has been badly affected by the shifting cultivation and forest fires. There are oak, alder, chestnut, birch, and cherry trees. There are a large variety of orchids, bamboo and creepers.

(i) Sub-tropical Pine forests

• Found in Shivalik Hills, Western and Central Himalayas, Khasi, Naga, and Manipur Hills.
• The trees predominantly found in these areas are the chir, oak, rhododendron, and pine as well as sal, amla, and laburnum are found in the lower regions.

(j) Sub-tropical Dry evergreen forests

• Hot and dry season and a cold winter. It generally has evergreen trees with shining leaves that have a varnished look, found in the Shivalik Hills and foothills of the Himalayas up to a height of 1000 metres.

(k) Montane Wet temperate forests

• In the North, found in the region to the east of Nepal into Arunachal Pradesh, receiving a minimum rainfall of 2000 mm. In the North, there are three layers of forests: the higher layer has mainly coniferous, the middle layer has deciduous trees such as the oak and the lowest layer is covered by rhododendron and champa.
• In the South, it is found in parts of the Niligiri Hills, the higher reaches of Kerala. 
• The forests in the northern region are denser than in the South. Rhododendrons and a variety of ground flora can be found here.

(l) Himalayan Moist temperate Forest

• This type spreads from the Western Himalayas to the Eastern Himalayas. The trees found in the western section are broad-leaved oak, brown oak, Walnut, rhododendron.
• Eastern Himalayas, the rainfall is much heavier and therefore the vegetation is also more lush and dense. There are a large variety of broad-leaved trees, ferri, and bamboo.

(m) Himalayan Dry temperate Forest

• This type is found in Lahul, Kinnaur, Sikkim, and other parts of the Himalayas.
• There are predominantly coniferous trees, along with broad-leaved trees such as the oak, maple, and ash. At higher elevation, fir, juniper, deodar, and chilgoza are found.

(n) Sub Alpine forest

• Subalpine forests extend from Kashmir to Arunachal Pradesh between 2900 to 3500 metres. In the Western Himalayas, the vegetation consists mainly of juniper, rhododendron, willow, and black currant.
• In the eastern parts, red fir, black juniper, birch, and larch are the common trees. Due to heavy rainfall and high humidity, the timberline in this part is higher than that in the West. Rhododendron of many species covers the hills in these parts.

(o) Moist Alpine scrub

• Moist alpines are found all along the Himalayas and on the higher hills near the Myanmar border. It has a low scrub, dense evergreen forest, consisting mainly of rhododendron and birch. Mosses and ferns cover the ground in patches. This region receives heavy snowfall.

(p) Dry Alpine scrub

• Dry alpines are found from about 3000 meters to about 4900 meters. Dwarf plants predominate, mainly the black juniper, the drooping juniper, honeysuckle, and willow.

3. Grassland Ecosystem

Grassland Ecosystem is an area where the vegetation is dominated by grasses and other herbaceous (non-woody) plants.  

• 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 are generally found in temperate climates.
  Grassland Ecosystem
• In India, they are found mainly in the high Himalayas. The rest of India’s grasslands are mainly composed of steppes and savannas. 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 savannas is that all the forage in the steppe is provided only during the brief wet season whereas in the savannas 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

(i) 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 gigantea, Cassia auriculata, Prosopis cineraria, Salvadora oleoides and ziziphus Nummularia which make the savanna rangeland look like scrub.

(ii) Dry subhumid zone (The Dichanthium- cenchrus- lasiurus type)

• It covers the whole of peninsular India (except Nilgiri). The thorny bushes are Acacia catechu, Mimosa, Zizyphus (ber) and sometimes fleshy Euphorbia, along with low trees of Anogeiss us latifolia, Soymida febrifuga 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.

(iii) Moist subhumid zone (The Phragmites- saccharum-imperata type)

• It covers the Ganga alluvial plain in Northern India.
• The topography is level, low lying, and ill-drained. 
• Bothriochloa pertusa, Cypodon dactylon and Dichanthium annulatum are found in transition zones. 
• The common trees and shrubs are Acacia arabica, hogeissus, latifolia, Butea monosperma, Phoenic sylvestris and Ziziphus nummularia. Some of these are replaced by Borassus sp in the palm savannas especially near Sunderbans.

(iv) 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 savanna 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.

• Fire plays, an important role in the management of grasslands. 
• Under moist conditions, fire favors grass over trees, whereas in dry conditions the fire is often necessary to maintain grasslands against the invasion of desert shrubs.
• Burning increases the forage yields.
  Example: Cynodon dactylon

4. Desert Ecosystem

A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life.  

• 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. 
  Desert Ecosystem
• Lack of rain in the mid-latitude is often due to stable high-pressure zones, deserts in temperate regions often lie in "rain shadows", which is where high mountains block off moisture from the seas. 
• The climate of these biomes is modified by altitude and latitude. At high, at a greater distance from the equator, the deserts are cold and hot near the 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

These plants conserve water by the following method:

• They are mostly shrubs. 
• Leaves are absent or reduced in size.
• Leaves and stems are succulent and water-storing. 
• In some plants, even the stem contains chlorophyll for photosynthesis. 
• The root system is well developed and spread over a large area. The annuals wherever present germinates, bloom and reproduce only during the short rainy season, and not in summer and winter.

• 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 characterized 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

• Depending directly upon rain. 
• Those depending on the presence of subterranean water.

1. The first group consists of two types:

• 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.

2. 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 taproot 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, Sandgrouse, and desert fox inhabit the open plains, grasslands, and saline depressions. 
• The nesting ground of Flamingoes and the only known population of Asiatic wild Ass lies in the remote part of Great Rarm, Gujarat. It is the migration flyway used by cranes and flamingos. 
• Some endemic flora species of the Thar Desert include Calligonum Polygonoides, Prosopis cineraria, Tecomella undulate, Cenchrus biflorus, and Sueda fruticosa, etc.

• The cold desert of India includes areas of Ladakh, Leh, and Kargil of Kashmir and Spiti valley of Himachal Pradesh, and some parts of northern Uttaranchal and Sikkim. Lies in the rain shadow of Himalayas. 
• Oak, pine, deodar, birch, and rhododendron are the important trees and bushes found there. Major animals 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).