Global Biome Distribution, Climate and Identification

Why climate helps determine a biome

A biome is a very large ecosystem with characteristic vegetation and animal life. Tropical forests, grasslands and tundra are different biomes because their environmental conditions support different kinds of living things.

At the global scale, climate is a major influence on biome distribution. Three important climatic factors are temperature, precipitation and sunshine hours. Together, they affect whether plants have enough warmth, water and light to grow. The vegetation then provides food and habitats for animals.

Temperature affects the length of the growing season. Warm conditions throughout the year allow continued growth, provided enough water is available. Long, freezing winters restrict growth to a short summer. Precipitation supplies water: a warm place can support dense forest if it is wet, but sparse vegetation if it is very dry. Light is needed for photosynthesis, so sunshine also influences plant growth and competition between plants.

Latitude, sunlight and seasonal growth

Biome patterns are connected to latitude because the amount of solar energy received varies across the Earth. Areas near the Equator are generally warmer than polar regions. This helps explain why tropical biomes are associated with warm climates, while tundra has a cold climate.

Seasonal light conditions also matter. In the far north, summer can bring almost continuous daylight, while winter brings little or none. Long summer days do not make tundra a warm, year-round growing environment: temperatures remain low and the growing season is short. Climate factors must therefore be considered together, rather than using sunshine alone to predict vegetation.

The seven major biomes

The main distinctions are the availability of water and the length and warmth of the growing season.

These are broad climate patterns, not fixed limits applying to every place. Notice especially that low precipitation does not necessarily mean heat: both deserts and tundra can be dry, but their temperatures and vegetation differ greatly. There are also cold deserts, such as the Gobi in northern China and southern Mongolia.

Tropical forests are not all rainforests. Tropical dry forests experience a dry season, during which many trees lose their leaves. This contrasts with the year-round growth supported by consistently warm, wet rainforest conditions.

Reading and comparing climate graphs

A climate graph puts the months in order along the horizontal axis. Precipitation is commonly shown by bars, measured in millimetres, while temperature is shown by a line, measured in degrees Celsius. Read the key and both vertical scales before interpreting it.

Begin with temperature. Identify the warmest and coldest months, then calculate the annual temperature range by subtracting the lowest monthly mean from the highest. Next examine precipitation: does it fall throughout the year, or is there a clear wet and dry season? Annual precipitation is the sum of the twelve monthly values, not the height of the tallest bar.

These graphs illustrate two contrasting climate patterns. In the tropical-forest example, temperature varies from 25°C to 27°C, giving a range of 2°C. Every month receives substantial precipitation. Warm, wet conditions therefore allow a long growing season.

In the boreal example, temperature varies from −15°C to 15°C, giving a much larger range of 30°C. Several months are below freezing, and precipitation is lower overall. The short, mild summer provides a much shorter growing season. A useful comparison therefore links the graph’s figures to the vegetation, rather than simply naming the two biomes.

Other patterns help distinguish biomes. A warm graph with a marked dry season suggests tropical grassland rather than rainforest. Very low precipitation suggests a dry biome, but temperature is needed to distinguish a hot desert pattern from a cold tundra pattern.

Locating the major biomes around the world

The following regions provide useful reference points when reading a world biome map:

• Tropical forests: rainforest occurs in South America around the Amazon, including Peru. Tropical dry forests occur in Africa, including Madagascar, India, southern Mexico and South America. Their warm climates support forest, but differences in water availability affect whether growth continues throughout the year.
• Tropical grasslands: savannas occur in Africa, South America and northern Australia. Their tropical warmth permits growth, but an extensive dry season helps explain the dominance of grasses rather than continuous forest.
• Deserts: the Sahara lies in northern Africa, the Namib in south-western Africa, and deserts also occupy parts of central Australia. Many subtropical deserts lie around 15–30° north and south of the Equator. Dry, descending air at these latitudes helps explain their low precipitation and sparse vegetation.
• Temperate grasslands: the prairies occupy central North America, while the steppes occur in Eurasia. Hot summers, cold winters and relatively low precipitation support seasonal grass growth rather than widespread forest.

Using a world biome map

A world biome map shows where biomes occur; a climate graph helps explain the conditions at a particular place. Start with the map’s legend: colours or shading represent different biome categories and must not be guessed. Find the Equator, identify the continents, and describe the mapped areas using continent names and positions such as northern, southern, coastal or interior.

For a concrete example, locate North America and then Canada. Use the legend to distinguish the boreal forest belt from tundra farther north. A useful description is that boreal forest extends across much of Canada, with Arctic tundra to its north. The explanation links this northward change to lower temperatures and a shorter growing season: coniferous forest gives way to low-growing vegetation as conditions become too cold for trees.

You can make a second comparison within Africa. Locate the Sahara in the north and the savanna regions farther south. Both include warm environments, so temperature alone cannot explain their different vegetation. The Sahara’s very low precipitation limits plant growth, whereas the savanna’s wet season supplies enough water for extensive grasses and scattered trees.

Apply this method to an authentic map by checking its actual key and boundaries. The regional examples above help you orient yourself, but do not replace reading the map. Places at similar latitudes can have different precipitation patterns, so latitude alone cannot identify a biome. Equally, a climate graph represents a particular location, not the exact climate of every part of a large biome.