Welcome to Biomes: Earth's Great Life Zones!

Hi Geographers! This chapter is all about Biomes—the largest, most awesome ecosystems on our planet. Since we are studying "Ecosystems under stress," we won't just look at where these biomes are, but critically examine how human actions are pushing them to the limit, especially in the context of development and population growth.

Understanding biomes helps us grasp the delicate balance of life on Earth and prepares us for discussing crucial issues like sustainability and biodiversity loss. Don't worry if some terms look new; we'll break them down step-by-step!


Key Concept 1: What is a Biome?

Think of a biome as a huge, global ecosystem. It’s defined primarily by its climate (temperature and precipitation) and the dominant types of vegetation that have adapted to that climate.

Defining the Biome

A Biome is a major regional or global biological community, characterised by the dominant plant life form and climate.

Biomes operate on a massive scale, grouping together many smaller, interconnected ecosystems.

Remember: The two most important factors determining which biome develops in a region are temperature and precipitation (rainfall).

Global Distribution of Major Terrestrial Biomes

The distribution of biomes follows global climatic zones, often linked closely to latitude.

  • Tropical Biomes: Found closest to the Equator (low latitude). Characterised by high temperatures year-round. (e.g., Tropical Rainforest, Savanna).
  • Mid-Latitude Biomes: Found further north and south (mid-latitude). Experience seasonal changes (e.g., Deciduous Forest).
  • High-Latitude Biomes: Found near the poles. Characterised by low temperatures (e.g., Tundra, Boreal Forest).

Did you know? Since biomes are primarily defined by climate, the global distribution reflects the Earth's main climate zones (e.g., tropical, temperate, polar).


Key Concept 2: Case Study – Tropical Rainforest (TRF)

The TRF is the poster child for biodiversity and is one of the biomes most heavily "under stress."

Main Characteristics of the Tropical Rainforest
  • Location: Low latitudes (within 10° North and South of the Equator). (Example: The Amazon Basin, Brazil).
  • Climate: Equatorial climate. High average temperatures (25-30°C) and extremely high, consistent rainfall (over 2,000mm annually). No distinct seasons.
  • Soil (Latols/Oxisols): These soils are deep, red, and highly weathered. They look fertile, but they are actually very infertile because high rainfall leaches (washes away) nutrients rapidly. Nutrients are stored in the biomass (the living vegetation).
  • Vegetation: Dense, layered, evergreen forest (high Net Primary Production – lots of energy converted into biomass).
Ecological Responses (Adaptations) in TRF

Plants and animals have incredible adaptations to deal with the high rainfall, deep shade, and nutrient-poor soil:

  • Flora Adaptations:
    - Stratification: Vegetation forms distinct layers (like a multi-story building): Shrub layer, under-canopy, canopy, and the emergent layer. This competition for sunlight drives adaptation.
    - Drip-Tips: Waxy leaves with pointed ends to shed water quickly, preventing moss or algae growth that could block photosynthesis.
    - Buttress Roots: Wide, shallow roots that offer immense stability in the shallow, nutrient-rich topsoil layer, preventing trees from falling over.
  • Fauna Adaptations:
    - Many animals are Arboreal (tree-dwelling) due to the dense canopy (e.g., monkeys, sloths).
    - Highly specialised diets (niches) to avoid competition in this diverse environment.
Human Activity and Impact in the TRF (Ecosystem under Stress)

Human activities here rapidly disrupt the fragile nutrient cycle and result in massive biodiversity loss.

  • Impact of Agriculture: Shifting cultivation (traditional, low impact) is replaced by large-scale cattle ranching (major cause of Amazon deforestation) or commercial mono-culture (like palm oil plantations).
  • Economic Development: Logging (hardwoods) and mining (e.g., iron ore, gold). Building roads for these industries opens up the forest to further settlement and destruction.
  • Implications for Sustainability: The TRF environment is highly unsustainable for large-scale, permanent agriculture because the soil nutrients are lost after just a few years of cultivation. Farmers are forced to move, creating a cycle of destruction.
  • Biodiversity Loss: Since 50% of global species live in the TRF, its destruction results in the extinction of species before they are even discovered.

Quick Review: TRF

The TRF is wet, hot, and nutrient-poor. Its greatest stress comes from economically-driven deforestation for ranching and logging, leading to unsustainable land use.


Key Concept 3: Case Study – Savanna Grassland (SG)

The Savanna is often found on the margins of the TRF. It experiences a seasonal climate, making it vulnerable to drought and, critically, desertification.

Main Characteristics of the Savanna Grassland
  • Location: Low latitudes, usually 5° to 20° North and South of the Equator. (Example: Serengeti, Tanzania or Maasai Mara, Kenya).
  • Climate: Tropical Wet and Dry climate. Experiences a distinct wet season (heavy rainfall, plant growth) and a long dry season (drought, high risk of fire).
  • Soils: Generally poor, prone to drying out (cracking/hardpans), and susceptible to erosion during intense rainfall events.
  • Vegetation: A mix of tall grasses and scattered, drought-resistant trees (e.g., Acacia and Baobab).
Ecological Responses (Adaptations) in Savanna

Life here must cope with extreme heat, drought, and frequent natural fires.

  • Flora Adaptations (Dealing with Water Stress):
    - Deep Roots: Trees like the Baobab have vast root systems to access groundwater during the dry season.
    - Deciduous Nature: Many trees shed leaves during the dry season to reduce water loss (transpiration).
    - Thick Bark: Fire-resistant to survive frequent savanna bush fires.
  • Fauna Adaptations (Dealing with Heat and Scarcity):
    - Migration: Large herds (e.g., wildebeest) undertake huge migrations to follow seasonal rainfall and fresh grass.
    - Burrowing: Smaller animals dig underground to escape the high temperatures and fires.
Human Activity and Impact in the Savanna (Ecosystem under Stress)

The primary stressor in the Savanna is often agricultural extension (converting natural grazing land to crops) and overgrazing, leading directly to land degradation and desertification.

  • Agricultural Extension: Converting marginal lands (dry savanna) for cash crops puts enormous strain on the soil and water balance.
  • Population Pressure: Rapid population growth forces pastoralists (herders) to keep larger herds or graze in smaller areas, leading to overgrazing, which kills grass roots and compacts the soil.
  • Development Issues & Water Balance: If rainfall reliability decreases (due to climate change) and human water abstraction increases, the soil moisture budget tips into deficit, accelerating land degradation.
  • Implications for Sustainability: The most critical issue is Desertification—the persistent degradation of dryland ecosystems. This is a mix of climate change (drought) and human impact (overgrazing, deforestation for fuel).

Quick Review: Savanna

The Savanna is seasonal (wet/dry). Its primary stress comes from human activities like overgrazing and agricultural conversion, which, combined with drought, pushes the ecosystem toward desertification.


Key Concept 4: Development Issues and Sustainability

When discussing biomes "under stress," you must link the physical characteristics (like climate and soil) to the human development challenges and the resulting environmental implications.

Comparing Development and Stress

The unique nature of each biome determines how humans exploit it and the stress that results.

TRF Development Issues
  • Economic Development: Driven by demand for valuable resources (hardwood, beef, minerals) in wealthy, developed nations.
  • Agricultural Intensification: Attempts at intensive farming fail quickly due to poor soil, leading to the "slash-and-burn" cycle and unsustainable use of land.
  • Population Change: Indigenous populations are displaced, and new settlers arrive via development roads, creating unplanned, rapid settlement and increased pressure on resources.
  • Implications for Sustainability: Global climate regulation (the TRF is a huge carbon sink) is severely threatened, leading to enhanced greenhouse effect. Biodiversity loss is irreversible.
Savanna Development Issues
  • Agricultural Extension: Pressure to expand cash crop farming into marginal areas, often displacing traditional pastoralists.
  • Population Change: High rural population growth strains the carrying capacity of the land, requiring larger herds (to feed more people) than the ecosystem can handle.
  • Impact on Soil Moisture Budget: Droughts are natural, but human action (overgrazing, removing trees) reduces soil infiltration and increases runoff and wind erosion. This permanently alters the soil moisture budget, making the land less productive and exacerbating desertification.
  • Implications for Sustainability: The loss of grazing land leads to conflict between different groups (farmers vs. herders) and internal or international migration (environmental refugees). Food security is severely compromised.

Analogy Time: The Biome Checkbook

Think of a biome's natural resources (soil, water, biomass) as a bank account.

In the TRF, all the "money" (nutrients) is in the "ceiling" (the biomass), not the "floor" (the soil). When you cut down the forest, you empty the bank account instantly, and you can't refill it.

In the Savanna, the "money" (soil moisture) is seasonal. If population pressure makes you withdraw too much "money" (graze too many animals or plant too many crops) during the dry season, you permanently break the system (desertification).


Final Takeaway

For your exam, always remember to connect the physical environment (climate, soil, water balance) to the human challenge (population growth, economic development needs) to explain the resulting environmental stress (deforestation, desertification) and its implications for biodiversity and sustainability. Great job getting through this tough section!