Characteristics and Climate of Major Ecosystems

The global distribution follows strict latitudinal patterns:

• Tropical Rainforests (TRF): 0–23.5° N/S. Centred on the equator across continents like South America (Amazon Basin) and Africa (Congo Basin).
• Tropical Grasslands (Savanna): 5–30° N/S. Located between rainforests and deserts, such as in Central Africa (Serengeti) and Northern Australia.
• Hot Deserts: 15–30° N/S. Found near the Tropics of Cancer and Capricorn, including the Sahara, Atacama, and Thar deserts.
• Temperate Deciduous Forests: 30–60° N/S. Primarily found in the Northern Hemisphere across the UK, Western Europe, and NE USA.
• Temperate Grasslands: 40–60° N/S. Located in continental interiors, such as the North American Prairies and Eurasian Steppes.
• Boreal Forests (Taiga): 50–70° N. A continuous belt across high latitudes in Scandinavia, Canada, and Russia.
• Tundra: 60–75° N. Found on the fringes of the Arctic Circle and coastal Greenland.

Local factors also alter distribution. Mountains in the tropics can host cold, tundra-like conditions because temperature drops by $6.5^\circ\text{C}$ per 1000m of altitude. Continentality creates extreme temperature ranges in inland areas, while ocean currents can warm coastal high-latitude regions.

The Characteristics of Forest Biomes

Forest ecosystems rely on a delicate interdependence between living (biotic factors) and non-living components (abiotic factors). A high level of biodiversity is found where these conditions are optimal.

The Tropical Rainforest is consistently hot ($27\text{--}30^\circ\text{C}$) and wet ($2000\text{--}3000\text{ mm}$ of rain annually), with NO distinct seasons. Due to heavy daily rain, the soils, called Latosols, suffer from intense leaching and are surprisingly nutrient-poor. To survive this environment, vegetation is highly stratified (layered) and features adaptations like buttress roots for stability, drip-tips to shed heavy water, and lianas that climb trees to reach sunlight.

Temperate Deciduous Forests experience four distinct seasons, with summers around $15\text{--}20^\circ\text{C}$ and winters staying above freezing. They receive moderate, year-round rain ($500\text{--}1500\text{ mm}$). Their soil, known as Brown Earth, is deep and highly fertile because deciduous broad-leaved trees drop their leaves in autumn, which then decompose.

Boreal Forests (Taiga) endure long, freezing winters (down to $-20^\circ\text{C}$) and short summers. Precipitation is low ($<500\text{ mm}$), mostly falling as snow. The soils, called Podsols, are thin, acidic, and nutrient-poor. Trees are coniferous and evergreen, featuring cone shapes to shed heavy snow and waxy needles to reduce water loss.

Grasslands, Deserts, and Tundra

Tropical Grasslands (Savanna) experience consistently high temperatures but have distinct wet and dry seasons, receiving $800\text{--}900\text{ mm}$ of rain. The soil contains a thin layer of humus but loses fertility due to wet-season leaching. The landscape is dominated by tall elephant grasses and scattered xerophytic trees, like the Baobab, which are adapted to survive long dry spells.

Temperate Grasslands endure extreme seasonality, ranging from $-40^\circ\text{C}$ in winter to $40^\circ\text{C}$ in summer due to continentality. They receive $250\text{--}750\text{ mm}$ of rain. Crucially, they are predominantly treeless, consisting of short tussock grasses growing in deep, dark, and incredibly fertile soils.

Hot Deserts receive very little rain ($<250\text{ mm}$) and have an extreme diurnal temperature range—reaching $50^\circ\text{C}$ by day but dropping below freezing at night. The sandy, rocky soils are called Aridisols; they contain almost NO organic matter and suffer from salinisation due to high evaporation rates.

The Tundra is effectively a "cold desert" receiving under $250\text{ mm}$ of precipitation, with temperatures remaining below $0^\circ\text{C}$ for up to 10 months of the year. The ground is permanently frozen, known as permafrost, meaning trees do NOT grow here. During the brief summer, a shallow, waterlogged active layer thaws, supporting low-growing cushion plants, mosses, and lichens that stay close to the ground to avoid freezing winds.

Comparing Climate Graphs

Climate graphs display average monthly temperature (as a line) and precipitation (as bars). Understanding how to interpret and compare these graphs is essential for identifying different biomes.

The essential calculations for comparing climates are:

$$Annual\ Temperature\ Range = Highest\ Monthly\ Temp - Lowest\ Monthly\ Temp$$ $$Total\ Annual\ Rainfall = Sum\ of\ all\ 12\ monthly\ precipitation\ bars$$

Worked Example: Comparing Tropical Rainforest and Tundra

Climate Feature	Tropical Rainforest (e.g., Manaus)	Tundra (e.g., Tiksi)	Comparison
Temperature Range	Remains steadily around $28^\circ\text{C}$ year-round, giving a low range of just $2^\circ\text{C}$.	Ranges from $10^\circ\text{C}$ in summer to $-30^\circ\text{C}$ in winter, giving a massive $40^\circ\text{C}$ range.	Difference: TRF has a very low temperature range, whereas Tundra experiences an extreme temperature range.
Total Precipitation	Bars are consistently high year-round, totalling over $2000\text{ mm}$.	Bars remain low year-round, totalling under $250\text{ mm}$.	Difference: TRF receives significantly more annual precipitation compared to the Tundra.<br><br>Similarity: Both biomes experience some precipitation in every single month of the year (neither has a completely dry month with $0\text{ mm}$).
Seasonality	The temperature line is perfectly horizontal, showing NO distinct seasons.	The temperature line forms a steep arch, indicating extreme thermal seasonality.	Difference: Tundra has extreme thermal seasons (with a growing season above $5^\circ\text{C}$ lasting only 2 to 3 months), in contrast to the seasonless TRF.