Global Biome Distribution and Ecosystem Basics

A biome is a large-scale ecological region defined by its climate and the characteristic plants and animals that live in it, while an ecosystem is a community of living organisms interacting with each other and with their non-living environment such as soil, water and air. In brief: the global distribution of biomes follows temperature and precipitation, which change with latitude and altitude: tropical rainforests lie near the equator, hot deserts and savannas in the tropics and subtropics, temperate forests and grasslands in the mid-latitudes, and boreal forest and tundra in the cold north.

Biomes explain why a forest in Brazil looks so different from one in Canada. This guide explains the basics of ecosystems and energy flow, how climate controls the biome map, lists the major biomes, compares them in a table, works through calculations of energy and temperature with height, outlines how the idea developed and corrects common mistakes.

What is an ecosystem?

An ecosystem has biotic (living) and abiotic (non-living) parts. The biotic parts are grouped by their role. Producers (plants and algae) capture sunlight through photosynthesis. Consumers (herbivores, carnivores and omnivores) eat other organisms. Decomposers (fungi and bacteria) break down dead material and return nutrients to the soil.

Energy flows through an ecosystem in one direction: from the Sun to producers and then through food chains and food webs to consumers. At each step, only about 10% of the energy passes to the next level, since most is lost as heat through life processes. Nutrients, by contrast, are recycled. Because of this energy loss, there are few top predators compared with the number of plants.

Why are biomes distributed as they are?

The main control is climate. Near the equator, the Sun’s rays are the most direct, so it is hot all year and there is heavy rainfall from the rising warm air of the intertropical convergence zone. At about 30° north and south, sinking dry air creates the belts of hot deserts. In the mid-latitudes, changeable weather and moderate rainfall support forests and grasslands. Toward the poles, temperatures fall and growing seasons shorten until only low tundra vegetation survives.

Altitude has a similar effect. Temperature falls by about 6 to 6.5 °C for every 1,000 m of height, so climbing a tropical mountain passes through zones resembling a trip toward the poles. Other influences include distance from the sea, ocean currents, rain-shadow effects behind mountains, soils and human activity. Net primary productivity (the new plant material produced per year) is highest in tropical rainforests and wetlands and lowest in deserts and the tundra.

Which are the major biomes?

• Tropical rainforest: hot and very wet all year, with very high biodiversity.
• Tropical seasonal forest and savanna: warm with wet and dry seasons; forest or grassland with scattered trees.
• Hot desert: very dry, with extreme daily temperature ranges.
• Mediterranean scrub: hot, dry summers and mild, wet winters, with tough evergreen shrubs.
• Temperate grassland: semi-dry with cold winters, dominated by grasses.
• Temperate deciduous forest: four seasons, with trees that lose their leaves in winter.
• Boreal forest (taiga): long cold winters and conifer trees.
• Tundra: very cold, treeless and often with permanently frozen ground.

Freshwater and marine ecosystems are sometimes counted as aquatic biomes. Mountain regions contain several biomes in a small vertical span.

Major biomes compared

Worked example: energy and altitude

1. Energy transfer: producers in a meadow capture 10,000 kJ of energy per square meter per year. With a 10% transfer, herbivores receive 1,000 kJ, primary carnivores 100 kJ and secondary carnivores 10 kJ.
2. Efficiency: the efficiency of a step is energy at the next level ÷ energy at the current level × 100. For herbivores eating plants, 1,000 ÷ 10,000 × 100 = 10%.
3. Temperature with height: a mountain base at sea level has a mean temperature of 28 °C. At 2,000 m, the drop is 2 × 6.5 = 13 °C, so the temperature is 28 − 13 = 15 °C.
4. Finding the height of a zone: if the temperature at the top is 4 °C, the drop from the base is 28 − 4 = 24 °C. Height = 24 ÷ 6.5 × 1,000 = about 3,700 m.
5. Rainfall per month: a forest receives 2,400 mm per year, an average of 2,400 ÷ 12 = 200 mm per month. A desert with 120 mm per year receives 10 mm per month, which is 20 times less.

How did the biome concept develop?

Alexander von Humboldt described the zones of vegetation on mountains and across the globe in the early 19th century. The German climatologist Wladimir Köppen created a climate classification around 1900 based on vegetation limits, which is still widely used. Frederic Clements, an American ecologist, introduced the term “biome” in the early 20th century, and Arthur Tansley proposed the term “ecosystem” in 1935. Later, Robert Whittaker plotted biomes against temperature and precipitation in a diagram that is now common in textbooks. Modern researchers use satellites to map vegetation and track how climate change shifts the boundaries.

Which mistakes are common?

Mistake 1: Confusing biome and ecosystem

A biome is a very large region with a typical climate and vegetation. An ecosystem can be as small as a pond.

Mistake 2: Thinking that energy is recycled like nutrients

Energy flows one way and is lost as heat. Only nutrients and matter cycle.

Mistake 3: Assuming sharp borders between biomes

Biomes grade into each other through transition zones called ecotones.

Mistake 4: Believing that biomes are fixed

Their boundaries have shifted over geological time and are shifting now with climate change and human land use.