Full study notes for BEVAE-181 Block 1 Unit 3. Covers all major types of ecosystems in detail — forest ecosystems (tropical, temperate, boreal), grassland ecosystems, aquatic ecosystems (ponds, lakes, rivers, marine), desert ecosystems, and wetland ecosystems. Explains the unique characteristics, flora, fauna, and ecological functions of each. Includes comparison diagrams, SAQs, and model answers for all terminal questions. Free PDF download.
Unit 3 · Index
In Unit 2 we studied what an ecosystem is and how it functions. Now we explore the major types of ecosystems on Earth — both terrestrial (forests, grasslands, deserts) and aquatic (freshwater, marine, estuaries). Each has unique characteristics, biota, and importance for human welfare and the planet.
The word ecosystem is made up of "eco" (habitat) and "system" (a complex set of interconnected components — both living and non-living). An ecosystem is a functional unit of nature.
📌 What is a Forest? The word "forest" comes from the Latin word foris meaning "outside" — referring to all uncultivated land outside the village boundary. Today, a forest is any land managed for the diverse purpose of forestry — whether covered with trees, shrubs, and climbers or not.
The forest ecosystem includes a complex assemblage of different kinds of biotic communities. The nature of soil, climate, and local topography determine the distribution and abundance of trees in forest vegetation.
Location: Cold regions with high rainfall, long winters, short summers. Transcontinental. (Also called "Taiga" in northern range.)
Plants: Evergreen species — Spruce (Picea glauca), Fir (Abies balsamea), Pine (Pinus roxburghii)
Animals: Lynx, wolf, bear, red fox, porcupine, squirrel, tree frogs, pond frogs
Soil: Acidic, mineral-deficient, slow litter decomposition. Productivity is lowest of all ecosystems.
Location: Moderate climate. North America, Europe, Eastern Asia (China, Japan), Chile, Australia. Annual rainfall: 75–150 cm.
Plants: Broad-leafed deciduous trees — shed leaves in winter, grow in spring. Maple (Acer), Beech (Fagus), Oak (Quercus), Hickory (Carya). In Himalayas: Pines, Cedars, Fir, Juniper, Rhododendrons.
Animals: Deer, bears, squirrels, gray foxes, wild turkey, woodpeckers, earthworms, snails, toads, salamanders, turtles, raccoons.
Location: Mediterranean-type climate — warm dry summers, cool moist winters.
Plants: Low evergreen trees — Hemlock, Yew, Maple. Shrubs 3–4m tall. (Woodland Chaparral)
Animals: Mule deer, brush rabbit, wood rat, chipmunk, lizard
Climate: Colder than other rainforests, marked seasonality. High rainfall + heavy fog (fog may be more important than rain!)
Biodiversity: Much lower than warmer rainforests.
Location: Near the equator. Most diverse communities on Earth. Annual rainfall > 200 cm, distributed throughout the year.
Plants: Highly diversified — 1 sq. km may contain 300 different tree species! Vertically stratified with canopy layer (25–35m), vines, creepers, lianas, epiphytic orchids. Dense evergreen carpet.
Animals: Arboreal amphibian Rhacophorus malabaricus, chameleons, agamids, geckos, leopards, jungle cats, ant-eaters, giant flying squirrels, monkeys, sloths.
Location: High total rainfall but with pronounced wet and dry seasons. Central India, South East Asia.
Plants: Teak is the major large tree. Bamboo is an important climax shrub.
Location: High rainfall, less temperature difference between winter and summer.
Plants: Broad-leaved evergreen — Mahogany, Palms, Oaks, Magnolias, Tamarind, with Epiphytes (Pineapple & Orchid families), Ferns, Vines, Strangler Fig (Ficus aureus).
Animal life: Very similar to tropical rain forests.
Fuel wood, pulp & paper, composite wood, rayon, matches, furniture, sport goods
Essential oils, medicinal plants, resins, turpentines, lac & shellac, katha, catechu, tasser silk, bidi wrappers
Forests provide habitat, food, and protection for countless wildlife species. They are reservoirs of genetic diversity.
Enhance local precipitation, improve water-holding capacity of soil, regulate water cycle, maintain soil fertility through litter
Check soil erosion, landslides; reduce intensity of floods and droughts
Important for tourism, recreation, and are the basis of many cultures and civilizations
Major threats: urbanization, agricultural expansion, and timber extraction. Key conservation and management techniques:
| Technique | What it means |
|---|---|
| Monoculture Forests | Planting fast-growing trees (poplar, eucalyptus) for timber or pulp — easier to manage but less biodiverse |
| Weeding | Eliminating species that compete with the seedlings of desired species |
| Thinning | Removing some individuals of the same species to improve growth |
| Brashing | Removing leafless lower branches, especially in conifers |
| Fire Control | Preventing and managing forest fires |
| Silviculture | Branch of forestry for establishment, development, care and reproduction of valuable timber trees like Teak, Sal, Sheesham, Kel |
i) Biotic communities
ii) Deciduous
iii) Equator
Direct services: Timber, fuel wood, pulp and paper, furniture, sport goods, medicinal plants, essential oils, resins, tasser silk, lac and shellac.
Indirect services: Regulate water cycle, enhance local precipitation, maintain soil fertility, check soil erosion and landslides, reduce floods and droughts, serve as reservoirs of genetic diversity, regulate Earth's climate, provide habitat for wildlife, aesthetic and cultural value.
Temperate Deciduous Forest: Broad-leafed deciduous trees that shed leaves in winter and grow new foliage in spring. Climate has cold winters and annual rainfall of 75–150 cm. Examples: Maple, Oak, Beech.
Temperate Evergreen Forest: Found in Mediterranean-type climate (warm dry summers, cool moist winters). Has low evergreen trees with needle-like or broad leaves — Hemlock, Yew, Maple. Does NOT shed leaves seasonally.
Grassland ecosystems are found where rainfall is about 25–75 cm per year — not enough to support a forest, but more than a true desert.
Typical grasslands are vegetation formations found in temperate climates. The grass layer is sparse and consists mainly of annual grass species. Grasslands go by different names in different regions:
All forage is provided ONLY during the brief wet season. Temperate grasslands of Eurasia.
Forage from grasses that grow during wet season AND have smaller regrowth in the dry season. Tropical grasslands (Africa).
Arid to semi-arid tracts. Active growth triggered by monsoon (June–July). Biomass peaks September–October. Dry by November.
🇮🇳 India's Grassland Example — Rajasthan (Dry Savanna): In central and eastern Rajasthan (rainfall ~500mm, dry season 6–8 months), dry savanna grazing ecosystems have developed. Sparse Prosopis cineraria trees provide light shade that favours grass growth — reaching heights of 100–120 cm in the best-watered areas.
India (with only 2.4% of world's land) supports: >50% of world's buffaloes, 15% cattle, 15% goats, 4% sheep
Horses, mules, cows, pigs, sheep, goats, buffaloes, camels, deer — provide food, milk, wool, hide, transportation
Livestock wealth plays a crucial role in Indian rural life as fuel, draught power, nutrition, and raw material for industries
Home for many wild herbivores like deer, zebra, and numerous bird species
⚠️ Overgrazing causes:
• Mulch cover of soil is reduced → exposed soil
• Microclimate becomes drier → invasion by xerophytic (drought-tolerant) plants
• Without humus cover, mineral soil surface gets heavily trampled
• Puddling of surface layer (when wet) → reduces infiltration of water into soil
• Accelerated surface runoff → soil erosion → land degradation
Grassland ecosystems are important because:
Overgrazing causes the following harmful ecological effects:
Deserts are formed in regions with less than 25 cm of annual rainfall, or in hot regions where more rain falls but is unevenly distributed. Deserts in temperate regions often lie in "rain shadows" — where high mountains block moisture from the sea.
🌍 Famous Deserts: Thar Desert (Western India & Pakistan), Sahara (North Africa), Gobi (Mongolia), Arabian Desert, Atacama (South America), Great Victorian Desert (Australia), Sinai (Egypt), Turkestan, Patagonian (Argentina)
Scattered throughout the desert ecosystem. Highly adapted to retain water.
Germinate, bloom, and reproduce ONLY during the short rainy season — NOT in summer or winter. Classic desert adaptation!
In salt deposits: Sarcobatus, Greasewood, Seepwood, salt grasses
Among reptiles: 2 species of testudines (Loricata), 18 species of lizards, 18 species of snakes. Lizards like Calotes versicolor and Uromastyx hardwickii are predatory on the desert locust in the Thar desert.
Among predatory birds: White-rumped vulture (Gyps bengalensis) and White scavenger vulture (Neophron percnopterus).
Among mammals: Rat-tailed bat, longer hedgehog, Indian hairy-footed gerbil, wild boar, jungle cat, panthers.
☀️ Desert Productivity: Because water is the dominant limiting factor, productivity of any desert is almost directly dependent on rainfall. Where soils are suitable, irrigation can convert deserts into some of our most productive agricultural land!
The Indian desert (Thar) is one of the most heavily populated desert regions in the world. According to the 2011 census, population densities vary from 361 persons/km² in Jhunjhunu to 17 persons/km² in Jaisalmer district.
Society: Villages have compact settlements and spread homesteads (dhanis). Desert society has many castes and sub-castes. The settled population is mostly agro-pastoral (~3/4 engaged in cultivation and agricultural labour). Animal husbandry is a supplementary occupation.
Problem: Total livestock population increased by 9.8 million from 1956–1981 and by more than 42% during 1972–1983. This enormous increase in human and livestock population is depleting natural resources at a rapid rate.
iii) Camel — The camel must drink periodically but is physiologically adapted to withstand tissue dehydration for appreciably long periods of time — a classic desert adaptation.
ii) Desert biome — Deserts experience intense heat, strong drying winds, and great desiccation (moisture removal) during the hot months of April to June.
i) Desert locust — The lizards Calotes versicolor and Uromastyx hardwickii are predatory on the desert locust in localised areas of the Thar desert.
Global waters cover about three-quarters of Earth's surface. Aquatic ecosystems are categorized based on salt content:
Salt content < 0.5%
Lakes, ponds, swamps, pools, springs, streams, rivers
Intermediate salt content
Estuaries, salt marshes, mangrove swamps and forests
Salt content > 3.5%
Shallow seas, open ocean
Organisms in aquatic ecosystems are unevenly distributed and classified into 5 groups based on their life form or location:
Five groups of aquatic organisms based on their life zone and movement abilities
| Group | Location/Lifestyle | Examples |
|---|---|---|
| Neuston | Surface film of water (air-water interface) | Water striders, beetles, back-swimmers, floating plants |
| Periphyton | Attached/clinging to stems and leaves of rooted plants above bottom mud | Sessile algae and associated animals |
| Plankton | Float in water, distribution controlled by currents (limited locomotion) | Phytoplankton (algae), Zooplankton (crustaceans, protozoans) |
| Nekton | Strong swimmers that overcome water currents | Swimming insects to Blue Whale (largest animal ever!) |
| Benthos | Live in or on the bottom (benthic region) | Crabs, lobsters, sponges, starfish, snails, clams |
Fresh water ecosystems depend on terrestrial ecosystems for large quantities of organic and inorganic matter constantly added by nearby land communities. Divided into two main types:
From Latin "lenis" = calm
Static bodies of water — Lakes, pools, ponds, swamps, marshes
Nutrients may be used several times (closed system except for some stream flow)
From Latin "lotus" = washed
Running water — Rivers, streams, springs, brooks
Open/heterotrophic system — plants and animals must use temporarily available nutrients
🏞️ Lakes: Inland depressions containing standing water. Most lakes formed within the past 20,000 years. But a few (Lake Baikal, Russia; Lake Tanganyika, Africa) are ancient — originated ~20 million years ago!
• Largest lake: Lake Superior (North America) — 83,000 km²
• Deepest lake: Lake Baikal (Siberia) — 706 m deep, 31,500 km²
• Some form in crater depressions of extinct volcanoes (crater lakes)
Loktak Lake is situated 38 km south of Imphal city, Manipur. It covers an area of about 286 sq. km.
Special feature: The lake has floating islands called Phumdis — heterogeneous masses of soil, vegetation, and organic matter (a few cm to 2.5 m thick). They occupy about two-thirds of the lake's surface.
Keibul Lamjao National Park: The largest single mass of phumdis (40 sq. km) constitutes this national park — home to the endangered Manipur brow-antlered deer (Sangai — Cervus eldi eldi).
Importance: Source of hydroelectric power, irrigation, and water supply. Rich in biodiversity. Designated as Ramsar Wetland of International Importance in 1990. Supports significant populations of migratory and resident waterfowl.
🌿 Wetlands: Permanently or periodically water-covered areas — submerged or saturated lands up to 6 metres deep. Two categories:
• Inland wetlands — surrounded by land, fresh water (e.g., bogs, swamps)
• Coastal wetlands — near coast, saline/brackish (e.g., mangrove swamps and forests)
Threat: Almost 40% of Assam's wetlands are under threat due to invasion of aquatic weeds and developmental activities (survey by ARSAC and Space Applications Centre, Ahmedabad). The wetlands of Assam can produce 5,000 t/ha/yr of fish, yet ~20,000 t of fish has to be imported — due to poor wetland management!
Rivers are open or heterotrophic systems — continuously flowing water that moulds the water bed and controls organism distribution. The two most important features:
Limiting factor: Speed of water current
Animals: Only organisms with efficient mechanisms to stay in place — freshwater limpet, larvae of water penny, freshwater sponges, caddis flies, stone flies, dragonflies.
Cold water fish (trout, salmon) found where current is not too strong. If current is very strong, nekton absent — benthos takes over.
Limiting factor: Dissolved oxygen availability
Animals: Annelids, flatworms, clams, snails, insect larvae found in microhabitats beneath rocks.
Plants: Only small, sessile algae. Nutrient base for animals is organic detritus washed in from drainage area.
🌊 Marine ecosystems are the largest and most stable systems on Earth. Sea water is salty with an average of 3.5% — of which NaCl (sodium chloride) is 27% of the salt. Other minerals: calcium, potassium, magnesium. Temperature ranges from 2°C (polar) to 32°C+ (tropics).
Ocean is divided into Littoral (shore), Neritic (shallow coastal), and Pelagic (open water) zones, with the Benthic zone at the ocean floor
| Zone | Description | Key Organisms |
|---|---|---|
| Littoral Zone | Shore region — exposed to waves, tides, temperature fluctuation. Also called "beach" (supra-littoral) | Snails, clams, barnacles, crustaceans, annelids, sea anemones, sea urchin. Animals show zonation with tides. |
| Neritic Zone | Shallow coastal — rich in species, high productivity (light penetrates + high nutrients) | Dinoflagellates, diatoms; Whales, seals, sea otters, sea snakes, sharks, sea trout, salmon; Clams, shrimps, crabs, lobsters, starfish, sponges |
| Pelagic Zone | Open ocean — 90% of ocean surface; less rich in species than neritic | Dinoflagellates, diatoms (photosynthetic); Sea cucumbers and sea urchins eating detritus; carnivorous brittle stars, crabs |
| Benthic Zone | Ocean floor — heterotrophic organisms | Sea lilies, sea fans, sponges (rooted animals); Snails and clams (in mud); Starfish, sea cucumbers, sea urchins (on surface) |
An estuary is a semi-enclosed part of the coastal ocean containing brackish water — having free connection with the sea on one side and connected with a river mouth on the other. It is a transitional zone between rivers and sea.
Estuaries are the most productive ecosystems in the world! They are found in plenty along the coast of Kerala and in the Sundarbans in India.
Estuaries form where rivers meet the sea — creating a unique brackish water habitat with fluctuating salinity
Four types of plants:
Key organisms:
Diatoms and filamentous blue-green algae (intense photosynthesis), Oysters, Crabs, Sea shrimps
🐟 Why Estuaries are So Important: Almost all major marine fisheries of the world are TOTALLY DEPENDENT on estuaries! Adult fishes often resort to estuaries for spawning (laying eggs). Estuaries serve as the nursery ground for a large number of fishes. They are also the most delicately balanced ecological systems — dumping garbage, sewage, or industrial waste into estuaries causes severe damage to this entire ecosystem!
Exam-style questions from the IGNOU textbook with complete model answers.
Forests are extremely important for human life and for the health of the planet. Their importance can be described under two categories:
Direct Importance (Products):
Indirect Importance (Ecological Services):
The dominant limiting factor in desert ecosystems is water scarcity. Both plants and animals have evolved remarkable adaptations to survive:
Desert Plant Adaptations:
Desert Animal Adaptations:
Grassland ecosystems are economically vital, especially in India:
In my view, the estuary is the most dynamic ecosystem on Earth, for the following reasons:
Note: Students may choose tropical rain forests (most biodiverse), coral reefs, or other ecosystems — as long as they give valid ecological reasons for their choice.
Marine Ecosystem:
Estuarine Ecosystem:
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