Terrestrial Biomes

Core Concepts

What makes a biome: temperature and precipitation

Biomes are primarily classified by annual temperature and precipitation patterns, not by individual species — the same-looking desert in Africa and North America may share no species at all, but both are deserts because both are hot and dry. Two extra factors refine the picture: seasonality (whether rain falls year-round or in distinct wet/dry seasons, and whether winters are cold) and soil (which stores water and nutrients). A good mental tool is to plot biomes on a temperature-by-precipitation grid: rainforests occupy the hot-and-wet corner, deserts the hot-and-dry corner, tundra the cold-and-dry corner, and boreal forest the cold-with-moderate-snow corner.

Tropical rainforest

Found near the equator, with warm temperatures year-round and very high rainfall (often over 200 cm per year). The result is the most species-rich biome on Earth: layered forest canopies, vines, epiphytes (plants growing on other plants), and animals like monkeys, parrots, and insects in enormous numbers. Ironically, tropical rainforest soils are usually thin and nutrient-poor — nearly all nutrients are tied up in living vegetation, and decomposers recycle fallen leaves so quickly that little accumulates in the soil. When the forest is cleared, the soil can support only a few years of farming before it is exhausted.

Savanna

Grasslands with scattered trees, found in tropical and subtropical regions with distinct wet and dry seasons (e.g., East Africa). Rainfall is too low or too seasonal for dense forest but enough for grasses. Large grazing herbivores (zebras, wildebeest, elephants) and their predators (lions, hyenas) are characteristic, and fire is a natural, recurring force that prevents trees from taking over and recycles nutrients into the soil.

Subtropical desert

Very low precipitation (often under 25 cm per year) and extreme temperature swings between day and night. Deserts are not always hot — cold deserts exist at high latitudes — but all are dry. Plants like cacti and other succulents store water and photosynthesize with reduced leaves; animals are nocturnal, burrowing, or highly water-efficient (kangaroo rats that never drink). Desert life is sparse but highly adapted; deserts cover about a fifth of Earth's land surface.

Chaparral

A shrubland biome found in Mediterranean-type climates — mild, wet winters and hot, dry summers — such as coastal California, the Mediterranean basin, and parts of Chile and Australia. Dense, drought-resistant shrubs and small trees dominate, and periodic wildfires are part of the natural cycle; many chaparral plants are adapted to resprout or reseed after fire. Human homes built into chaparral face a growing wildfire risk, especially as climates dry.

Temperate grassland

Found in mid-latitude regions with hot summers, cold winters, and moderate rainfall too low for forests — the prairies of North America, the steppes of Eurasia, the pampas of South America. Deep, fertile soils built up over millennia by grass root systems make this the most productive agricultural biome on Earth; most original temperate grassland has been converted to cropland. Fire and grazing by large herbivores (bison, pronghorn) maintain the grass-dominated community.

Temperate forest

Mid-latitude regions with moderate rainfall and distinct seasons, dominated by deciduous trees (oak, maple, beech) that lose their leaves in winter, or by evergreen conifers in some regions. These forests have well-developed soil layers, abundant decomposers, and rich animal life (deer, bears, birds). Much of eastern North America, Europe, and East Asia was originally temperate deciduous forest, and because the soil is fertile, much has been cleared for agriculture and cities — though large tracts remain.

Boreal forest (taiga)

The world's largest terrestrial biome, a broad band of coniferous forest (spruce, fir, pine) across Canada, Scandinavia, and Russia just south of the tundra. Winters are long and cold, summers short; precipitation is modest but low evaporation keeps it humid. Trees are adapted to cold with needle-like leaves and conical shapes that shed snow. The taiga stores enormous amounts of carbon in its trees and especially in thick, acidic soils and peat, making it globally important for climate.

Arctic tundra

Found at the highest latitudes and on high mountains (alpine tundra), where winters are long and bitterly cold and summers are brief. Permafrost — permanently frozen subsoil — prevents deep root growth, so vegetation is limited to low shrubs, grasses, mosses, and lichens. The growing season is very short, and the entire biome is low in productivity and species diversity. As the climate warms, thawing permafrost releases stored carbon and methane, a feedback that amplifies warming.

Common Confusions