Year 9 Geography · Geography · 9m read

Biomes and Ecosystems

Ever wondered why rainforests are so wet and jungly while deserts are bone-dry? That's all about biomes — massive regions on Earth with similar climate, plants, and animals that fit together like a puzzle. Understanding what makes each biome tick (temperature, rainfall, and soil type) helps you see why polar bears live at the poles while kangaroos thrive in the outback, and it's crucial for VCE geography and understanding how climate change threatens these delicate ecosystems.

Learning objective: Explain the characteristics of the major biomes and factors that determine their distribution.

By the end of this lesson you can:

• I can name and describe the major biomes.
• I can explain how climate determines biome location.
• I can describe the ecological functions of a biome.

Biomes are Earth's neighbourhoods. Each neighbourhood has its own climate, plants and animals — rainforest, desert, tundra — shaped by temperature and rainfall.

Major biomes of the world

BIOME: A large-scale ecological community defined by its climate, vegetation and animals.

MAJOR BIOMES:
• TROPICAL RAINFOREST — hot and wet year-round; Amazon, Congo, Southeast Asia. Highest biodiversity on Earth.
• SAVANNA — seasonal wet/dry; Africa, Australia. Grasslands with scattered trees.
• DESERT — low rainfall (<250 mm/yr); hot or cold. Sahara, Australian Outback, Gobi.
• TEMPERATE GRASSLAND — interior continents; prairies (North America), steppes (Eurasia).
• TEMPERATE FOREST — four seasons; oaks, beeches; Europe, eastern USA, eastern Australia.
• BOREAL FOREST (TAIGA) — cold; conifer forests across Canada, Russia, Scandinavia.
• TUNDRA — permafrost; treeless; Arctic regions.
• MEDITERRANEAN — dry summer, wet winter; California, southern Australia, Mediterranean Basin.

WHAT CONTROLS BIOME DISTRIBUTION?
• TEMPERATURE (latitude and altitude).
• PRECIPITATION (amount and seasonality).
• SOILS — developed over thousands of years, reflect climate and vegetation.

AUSTRALIA'S BIOMES:
• Desert and semi-arid zones cover ~70% of the continent.
• Tropical rainforest in Queensland; Mediterranean scrub in SW WA.
• Unique fauna (kangaroos, eucalypts) due to long isolation.

AARI TIP: Ask Aari to compare the Amazon rainforest and Australian tropical north ecosystems.

Biome quick facts

• Latitude → climate: Tropics: hot/wet. Poles: cold/dry.
• Altitude mimics latitude: Higher = colder = different biome.
• Biodiversity hotspot: Tropical rainforests hold ~50% of species.

Quick reference

| Biome | Climate | Example |
|---|---|---|
| Tropical rainforest | Hot, wet | Amazon, Daintree |
| Desert | Very dry | Sahara, Simpson |
| Grassland | Seasonal rain | Savanna |
| Temperate forest | Mild | Victoria |
| Tundra | Very cold | Arctic |

Worked example (Medium)

Why does Australia have such large desert and semi-arid zones?

1. Location. Much of Australia lies between 20°S–35°S, in the subtropical high-pressure belt.
2. High pressure. Descending dry air suppresses rainfall — creating dry conditions across the interior.
3. Distance from sea. The interior is far from moisture-bearing ocean winds.
4. Result. The combination of latitude, atmospheric circulation and continental size produces vast arid zones.

Answer: Subtropical high-pressure systems and distance from the coast combine to produce Australia's vast arid interior.

Worked example (Hard)

Compare and contrast the tropical rainforest and tundra biomes, explaining how climate produces their distinctive ecological features.

1. Climate comparison. Tropical rainforests have consistently high temperatures (~25–30 °C) and heavy rainfall (>2 000 mm/yr). Tundra has extreme cold (annual average about −10 °C) and very low precipitation (<250 mm/yr), mostly as snow.
2. Vegetation contrast. Rainforests have a dense, multi-layered canopy of broadleaf evergreens because constant warmth and moisture allow year-round photosynthesis. Tundra vegetation is limited to mosses, lichens and low shrubs because permafrost prevents deep root growth.
3. Biodiversity. Rainforests host ~50 % of all species on Earth — warmth and moisture create countless ecological niches. Tundra has very low biodiversity; only highly specialised organisms (caribou, Arctic fox) survive the extreme cold.
4. Soils and nutrient cycling. Rainforest soils are often nutrient-poor because rapid decomposition recycles nutrients straight back to living plants. Tundra soils are thin, frozen (permafrost) and waterlogged in the brief summer thaw, limiting plant growth further.

Answer: Climate extremes produce radically different ecosystems — warmth and moisture create complexity and biodiversity, while cold and aridity limit life to highly specialised organisms.

Common mistakes

• Confusing "weather" with "climate" Weather is short-term atmospheric conditions; climate is the long-term average (30+ years) that defines a biome. Using them interchangeably leads to inaccurate explanations. Fix: Always specify: "The climate of the Sahara is hot and dry" (long-term), not "The weather of the Sahara is hot and dry."
• Assuming all deserts are hot Students forget cold deserts exist (e.g. Gobi, Antarctica). Desert is defined by low precipitation (<250 mm/yr), not high temperature. Fix: Define desert by rainfall, then distinguish hot deserts (Sahara) from cold deserts (Gobi).
• Drawing sharp boundaries between biomes In reality, biomes grade into one another through transition zones called ecotones, not neat lines on a map. Fix: Describe transitions — e.g. "The savanna gradually gives way to tropical rainforest as rainfall increases."

Ecotones — where biomes meet

In textbooks, biomes appear as neat blocks of colour, but reality is far more complex. The boundaries between biomes are ecotones — transition zones where characteristics of adjacent biomes blend together. For example, the shift from tropical rainforest to savanna in northern Australia involves a gradual decrease in tree density and canopy height as rainfall becomes more seasonal.

Ecotones matter for several reasons. First, they often harbour species from *both* adjacent biomes, creating surprisingly high local biodiversity. Second, they are climate-sensitive indicators: as global temperatures rise, ecotones are among the first places where biome shifts become visible. Scientists monitoring the Sahel — the ecotone between the Sahara and the savanna — have observed both desertification and, in some areas, unexpected "greening" as rainfall patterns change.

Understanding ecotones challenges the simplistic view of biomes as fixed and unchanging. They remind us that ecosystems are dynamic, responding to both natural variability and human-induced climate change. For geographers, ecotones provide critical early-warning evidence of how global warming is reshaping Earth's ecological zones in real time.

Practice questions

1. Which biome has the highest biodiversity on Earth?

   1. Temperate forest
   2. Tundra
   3. Tropical rainforest
   4. Savanna

   (1 marks)

2. Explain how climate determines the type of vegetation found in a biome.

   (3 marks)

Summary

• Name and describe the major biomes.
• Explain how climate determines biome location.
• Describe the ecological functions of a biome.