Class 7 Social Science Notes Chapter 8 (Human Environment Interactions The Tropical and the Subtropical Region) – Our Environment Book

Alright class, let's focus on Chapter 8, 'Human Environment Interactions: The Tropical and the Subtropical Region'. This chapter is crucial as it compares life in two distinct climatic zones and how humans adapt. Pay close attention, as these details often appear in competitive exams.

Chapter 8: Human Environment Interactions – The Tropical and the Subtropical Region

This chapter explores life in two major river basins:

1. The Amazon Basin (Tropical Region)
2. The Ganga-Brahmaputra Basin (Subtropical Region)

I. Life in the Amazon Basin

• Location:

  • Located in South America.
  • Lies very close to the Equator (between 10°N and 10°S latitude), hence referred to as the equatorial region.
  • The Amazon River flows through this region, originating from the Andes Mountains and draining into the Atlantic Ocean.
  • The river basin covers portions of Brazil, Peru, Bolivia, Ecuador, Colombia, and a small part of Venezuela.
  • The Amazon is the world's largest river by discharge volume of water.
  • Numerous tributaries join the Amazon River to form the Amazon Basin.

• Climate:

  • Equatorial Climate: Characterized by hot and wet conditions throughout the year.
  • Temperature: High temperatures consistently, with very little variation between day and night. Both day and night are almost equally hot and humid.
  • Rainfall: Heavy rainfall occurs almost daily, usually in the afternoon, often without much warning (convectional rainfall). This leads to high humidity.

• Natural Vegetation (Flora): Rainforests

  • Dense Forests: Heavy rainfall supports thick, dense forests known as tropical rainforests or 'Selvas'.
  • Canopy: The trees form a dense roof or 'canopy' with their leaves and branches, preventing sunlight from reaching the ground significantly. The ground remains dark and damp.
  • Vegetation Layers: Forests have multiple layers of vegetation. Only shade-tolerant vegetation grows on the forest floor.
  • Rich Biodiversity: Home to a vast variety of plant species.
  • Plant Life: Orchids and bromeliads grow as plant parasites (epiphytes – growing on other plants). Important trees include mahogany, ebony, rosewood, and rubber.

• Wildlife (Fauna):

  • Rich Biodiversity: The rainforests teem with diverse animal life.
  • Mammals: Monkeys, sloths, ant-eating tapirs.
  • Birds: Toucans (with oversized, colourful bills), hummingbirds, birds of paradise.
  • Reptiles & Amphibians: Snakes (including anacondas and boa constrictors), lizards, crocodiles, frogs.
  • Insects: Various species of insects abound.
  • Fish: Several species of fish, including the flesh-eating Piranha fish and giant fish like the Arapaima, are found in the river.

• People and Human Activities:

  • Population Density: Sparsely populated due to dense forests and climate.
  • Main Activities: Hunting, fishing, and agriculture.
  • Agriculture:
    • Shifting Cultivation (Slash and Burn): Predominant method. Farmers clear a patch of forest by cutting and burning trees. Crops are grown in the ash-fertilized soil for a few years until the soil loses fertility. Then, the farmers move to a new plot, allowing the old one to regenerate. Known locally by various names.
    • Main Crops: Tapioca, pineapple, sweet potato. Manioc (also known as cassava) is the staple food.
    • Cash Crops: Coffee, maize, and cocoa are also grown.
  • Housing: People live in thatched houses shaped like beehives. Large, apartment-like thatched houses called "Maloca" with steeply slanting roofs are common for community living.
  • Impact of Development:
    • Developmental activities (road construction like the Trans-Amazon Highway, mining, industrial activities, large-scale agriculture) are leading to gradual destruction of the rainforests (deforestation).
    • This deforestation has far-reaching consequences, including loss of biodiversity, soil erosion, and impact on climate patterns.
    • Indigenous cultures and ways of life are also threatened.

II. Life in the Ganga-Brahmaputra Basin

• Location:

  • Located in the Indian subcontinent.
  • Lies in the sub-tropical region (approximately 10°N to 30°N latitude).
  • The basin is formed by the Ganga and Brahmaputra rivers and their numerous tributaries (e.g., Ghaghra, Son, Chambal, Gandak, Kosi for Ganga; Teesta, Manas for Brahmaputra).
  • Covers parts of India (Northern Plains, parts of Himalayas) and Bangladesh.

• Physical Features:

  • Dominated by the fertile plains formed by the alluvial deposits of the Ganga and Brahmaputra rivers.
  • Includes mountainous regions (Himalayas and their foothills) to the north and the Sundarbans delta where the rivers meet the Bay of Bengal.
  • Ox-bow lakes are common in the plain area.

• Climate:

  • Monsoon Climate: Characterized by distinct seasons.
  • Summers: Hot and dry.
  • Monsoon Season: Receives most of its rainfall during the monsoon months (mid-June to mid-September).
  • Winters: Cool.
  • Rainfall distribution varies across the basin.

• Natural Vegetation (Flora):

  • Vegetation varies according to the topography and rainfall.
  • Plains: Tropical deciduous forests dominate, with trees like teak, sal, peepal, and shisham shedding their leaves in the dry summer. Thick bamboo groves are common in the Brahmaputra plain.
  • Delta Region (Sundarbans): Covered with mangrove forests. The Sundari tree is prominent here, giving the delta its name.
  • Mountainous Areas: Coniferous trees like pine, deodar, and fir are found at higher altitudes in parts of Uttarakhand, Sikkim, and Arunachal Pradesh, where slopes are steep and the climate is cool.

• Wildlife (Fauna):

  • Varied Wildlife: Diverse fauna reflecting the varied environments.
  • Mammals: Elephants, tigers (especially the Royal Bengal Tiger in Sundarbans), deer, monkeys are common. The one-horned rhinoceros is found in the Brahmaputra plain (Assam).
  • Reptiles: Crocodiles and gharials (alligators) are found in the rivers.
  • Aquatic Life: Abundant aquatic life in the fresh river waters and the Bay of Bengal. Popular varieties of fish include rohu, catla, and hilsa.
  • River Dolphin: The endangered freshwater dolphin, locally known as 'Susu' (also called Blind Dolphin), is found in the Ganga and Brahmaputra rivers. Its presence indicates the health of the river.

• People and Human Activities:

  • Population Density: The plains area has a very high population density due to fertile land suitable for agriculture.
  • Main Occupation: Agriculture is the primary occupation. The flat land, fertile soil, and adequate water supply support intensive farming.
  • Agriculture:
    • Main Crop: Paddy (Rice) is the staple crop, requiring high rainfall.
    • Other Crops: Wheat, maize, sorghum, gram, and millets are grown.
    • Cash Crops: Sugarcane and jute are important cash crops. Banana plantations are seen in some areas.
    • Plantations: Tea is grown in plantations in West Bengal and Assam.
    • Sericulture: Silk is produced through the cultivation of silkworms (sericulture) in parts of Bihar and Assam.
  • Settlements: Numerous large towns and cities are located along the river banks, e.g., Allahabad (Prayagraj), Kanpur, Varanasi, Lucknow, Patna, Kolkata (on River Hooghly, a distributary of Ganga), Delhi (on River Yamuna, a tributary of Ganga), Guwahati (on River Brahmaputra).
  • Terrace Farming: In the mountainous areas, terraces are cut into slopes to practice agriculture.
  • Impact of Human Activities:
    • Pollution: All four modes of transport (roadways, railways, waterways, airways) are well-developed. However, waste from towns, cities, and industries is discharged into the rivers, leading to severe pollution. This threatens aquatic life (like the Susu) and human health.
    • Conservation Efforts: Initiatives like the 'Namami Gange Programme' have been launched to clean the River Ganga. Efforts are ongoing to promote sanitation, sewage treatment, and reduce industrial pollution.
  • Tourism: An important activity in the region. Key sites include the Taj Mahal (Agra, on Yamuna), Buddhist stupas (Uttar Pradesh, Bihar), Lucknow (Imambara), Kaziranga and Manas wildlife sanctuaries (Assam), and Arunachal Pradesh (distinct tribal culture).

Key Differences Summarized:

Multiple Choice Questions (MCQs):

1. The Amazon Basin is primarily located in which climatic region?
   a) Temperate
   b) Subtropical
   c) Equatorial
   d) Arctic

2. Which type of agriculture is commonly practiced by people in the Amazon rainforests?
   a) Terrace farming
   b) Intensive farming
   c) Slash and Burn agriculture
   d) Plantation agriculture

3. 'Maloca' refers to:
   a) A type of fish found in the Amazon river
   b) Large apartment-like houses in the Amazon basin
   c) A tributary of the Ganga river
   d) A specific type of bird in the rainforest

4. The Ganga-Brahmaputra basin lies mainly in which latitudinal range?
   a) 0° - 10°N
   b) 10°N - 30°N
   c) 30°N - 40°N
   d) 10°S - 10°N

5. Which type of forest is characteristic of the Sundarbans delta in the Ganga-Brahmaputra basin?
   a) Coniferous forest
   b) Tropical evergreen forest
   c) Mangrove forest
   d) Deciduous forest

6. The one-horned rhinoceros is predominantly found in which part of the Ganga-Brahmaputra basin?
   a) Sundarbans delta
   b) Himalayan foothills
   c) Brahmaputra plain (Assam)
   d) Plains of Uttar Pradesh

7. What is the staple food crop in the densely populated plains of the Ganga-Brahmaputra basin?
   a) Maize
   b) Wheat
   c) Manioc
   d) Paddy (Rice)

8. 'Susu', found in the Ganga and Brahmaputra rivers, refers to a variety of:
   a) Fish
   b) Crocodile
   c) River Dolphin
   d) Water snake

9. Which of the following cash crops is significantly grown in the Ganga-Brahmaputra basin, especially in West Bengal and Assam?
   a) Coffee
   b) Rubber
   c) Tea
   d) Cocoa

10. The primary environmental concern highlighted in the Ganga-Brahmaputra basin is:
    a) Deforestation
    b) Desertification
    c) River pollution
    d) Soil erosion due to shifting cultivation

Answer Key for MCQs:

1. c) Equatorial
2. c) Slash and Burn agriculture
3. b) Large apartment-like houses in the Amazon basin
4. b) 10°N - 30°N
5. c) Mangrove forest
6. c) Brahmaputra plain (Assam)
7. d) Paddy (Rice)
8. c) River Dolphin
9. c) Tea
10. c) River pollution

Make sure you revise these notes thoroughly. Understanding the interplay between the environment and human life in these distinct regions is key. Good luck with your preparation!