Biomes of the World

Look at Earth from orbit and you see it instantly — a pattern of colour and texture imposed on the planet’s surface that corresponds neither to national borders nor to human intention. The dark green belt wrapping equatorial continents. The ochre and tan of the subtropical desert bands. The silver-green shading of temperate latitudes. The olive-grey of boreal forest stretching from Alaska to Siberia. The white of Arctic and Antarctic regions. These patterns are biomes — large-scale ecological zones defined by climate and expressed through the life that inhabits them. Every organism you can name lives in a biome. Every food you eat was produced in one. Every breath of oxygen you take was generated by photosynthesising organisms distributed across biomes from tropical rainforest canopies to open-ocean phytoplankton. Understanding biomes is understanding the ecological architecture of the living planet. According to the World Wildlife Fund’s biome overview, Earth’s major biomes can be mapped onto distinct climate envelopes, and the health of those biomes is inextricably tied to human welfare at every scale from local to global.

What Is a Biome — Definition, Scale, and Classification Systems

The concept of the biome as a fundamental unit of ecological organisation dates to Frederic Clements and Victor Shelford’s 1939 text Bio-ecology, though the underlying idea — that climate produces recognisable, repeating vegetation patterns at continental and global scales — was articulated by Alexander von Humboldt in the early nineteenth century. Humboldt’s observations during his South American expeditions, particularly the systematic change in vegetation structure with altitude on the Andes (which mirrors the change with latitude across continents), established the principle that physical environment determines the life forms (not just the species) present in a location. That principle is the foundation of biome ecology.

Climate Drivers — How Temperature and Precipitation Shape Biomes

Two variables — mean annual temperature (MAT) and mean annual precipitation (MAP) — account for approximately 65–75% of the variance in global vegetation patterns, making them the primary determinants of which biome type develops at any location. But the relationship is not simply linear: seasonality (the concentration of temperature or rainfall in particular months) is often as important as the annual total. A location receiving 1,000 mm of rainfall distributed evenly across 12 months supports temperate deciduous or mixed forest; the same 1,000 mm concentrated in 6 months with a pronounced dry season supports tropical savanna. A mean annual temperature of 5°C could characterise a boreal forest (if precipitation is moderate) or a semi-arid steppe (if precipitation is low).

Beyond temperature and precipitation, three additional environmental drivers shape biome boundaries: seasonality (the annual variation in temperature and rainfall — continental interiors experience greater temperature seasonality than coastal regions at the same latitude, producing differences between maritime temperate forest and continental steppe); soil type (the underlying geology and pedogenic processes determine nutrient availability, drainage, and pH — the same rainfall and temperature can produce tropical rainforest on nutrient-rich volcanic soils and nutrient-poor white-sand forest on podzolic soils within a few kilometres); and disturbance regime (fire frequency, flooding, wind, and large-herbivore grazing all maintain biome states that climate alone might not predict — the tropical savanna biome exists partly because C4 grasses accumulate enough biomass to carry fires that kill tree seedlings, maintaining the open structure even where precipitation could theoretically support closed forest). These interactions between climate, soil, and disturbance explain why simple temperature-precipitation models cannot perfectly predict biome type at every location.

Tropical Rainforest — Earth’s Biodiversity Engine

Tropical Savanna and Dry Forest — Fire, Seasonality, and the World’s Largest Herbivore Systems

The tropical savanna biome covers approximately 20% of Earth’s land surface — more than any other terrestrial biome — and supports the planet’s most spectacular concentrations of large terrestrial herbivores. It is a biome defined fundamentally by contradiction: enough rainfall (500–1,500 mm/yr) to support closed-canopy forest, yet dominated by open grassland with scattered trees. This apparent contradiction is resolved by the interplay of three factors: a strongly seasonal rainfall regime that creates a months-long dry season during which grasses senesce and fuel intense fires; a community of large grazing mammals (in Africa, up to 90 herbivore species in the Serengeti-Mara ecosystem alone) that prevent tree seedling establishment; and soil conditions (particularly the impermeable laterite horizons of tropical Africa) that limit deep-rooted trees while favouring shallow-rooted grasses.

Desert Biomes — the World’s Driest Landscapes

Deserts cover approximately 20–25% of Earth’s land surface and are defined not by heat but by aridity: precipitation consistently less than potential evapotranspiration, producing a water deficit that most life forms cannot tolerate. Some deserts are cold year-round; others experience extreme heat. What unites them is the challenge of chronic water scarcity — and the extraordinary diversity of adaptations that organisms have evolved in response. Far from the barren wastelands of popular imagination, deserts are biologically active, geologically dramatic, and ecologically distinct environments that harbour their own specialised, highly adapted communities of organisms.

Mediterranean Shrubland — the Biome of Convergent Fire Adaptation

The Mediterranean shrubland biome — known as chaparral in California, maquis or garrigue in Mediterranean Europe and North Africa, fynbos in South Africa, kwongan in southwestern Australia, and matorral in Chile — is one of Earth’s most striking examples of convergent evolution. Five separate regions of the world, located at 30°–45° latitude on the western sides of continents, share an identical climate regime: hot, dry summers (virtually no rainfall from June–September in the northern hemisphere) and mild, wet winters. In response to this identical selective pressure, entirely unrelated plant lineages on five continents have independently evolved the same suite of adaptations — small, leathery (sclerophyllous) leaves with thick cuticles, deep root systems accessing permanent groundwater, serotinous cones or hard-coated seeds requiring heat to germinate, and thick bark or lignotubers enabling post-fire resprouting.

The South African fynbos deserves special note for its extraordinary plant diversity. Covering just 88,000 km² (about the size of Portugal) in the Cape Floristic Region of South Africa’s Western Cape, the fynbos contains approximately 8,500–9,000 vascular plant species of which approximately 70% are endemic — giving it a higher plant species density than any equivalent area in the tropical rainforest. This diversity is driven by the fire-prone ecology (most fynbos plants are killed by fire but regenerate from seed or lignotuber), the varied soil chemistry (Cape soils range from nutrient-extremely-poor Table Mountain sandstone to calcareous dune sands), and the ancient age and geographic isolation of the region. The fynbos is the world’s smallest but most biodiverse floral kingdom, officially recognised as the Cape Floristic Region biodiversity hotspot.

Temperate Grassland — Prairie, Steppe, Pampas, and Veld

Temperate grasslands — called prairie in North America, steppe in Central Eurasia, pampas in South America, and veld in South Africa — cover approximately 8–9% of Earth’s land surface and are characterised by dominance of grasses and forbs (non-woody flowering plants), a near-absence of trees (except along watercourses), and the deep, organically rich soils (Mollisols) that make them the world’s most productive agricultural land. The deep black soils of the North American prairie, the Ukrainian chernozem steppe, and the Argentine pampas represent the accumulated organic matter of thousands of years of grass growth, death, and decomposition in a climate where low rainfall limits decomposition rates — making them among the most fertile soils on Earth but also the most thoroughly converted by ploughing.

Temperate Deciduous Forest — Autumn, Dormancy, and Seasonal Diversity

The temperate deciduous forest biome occupies the moderate-temperature, moderate-precipitation zone of eastern North America, western and central Europe, and eastern China and Japan — regions where temperatures below freezing for 2–5 months each year prevent year-round photosynthesis, and where summer rainfall (600–1,500 mm/yr distributed across the growing season) is sufficient to support broadleaved trees. The deciduous habit — losing all leaves in autumn and regenerating them in spring — is the dominant forest strategy in these climates, enabling trees to avoid the physiological stress of freezing temperatures while having liquid water unavailable, at the cost of the seasonal energy and nutrient investment required to rebuild a canopy each spring.

The seasonal dynamics of temperate deciduous forests create some of the most dramatic ecological cycles visible to a human observer: the vernal explosion of light-demanding spring ephemerals (Trillium, Hepatica, Bloodroot) flowering before the canopy leafs out and shading the forest floor; the summer canopy at full leaf, casting dense shade and supporting complex food webs of caterpillars, leaf-mining insects, and associated insectivorous birds; the autumn colour (driven by the breakdown of chlorophyll revealing carotenoids, combined with production of anthocyanins — possibly as sunscreen protecting nutrient resorption); and the stark winter forest with its leafless silhouettes. This seasonality drives synchronised breeding (birds migrating north in spring to exploit the caterpillar eruption), migration (monarch butterflies, warblers, hawks), and dormancy (bears, groundhogs, woodland dormice hibernating through the food-poor winter).

Boreal Forest (Taiga) — the World’s Largest Land Biome

The boreal forest — or taiga — is the world’s single largest terrestrial biome, forming a near-continuous belt of coniferous forest encircling the northern hemisphere at latitudes 50°–70°N and covering approximately 11–15 million km². To place this in perspective: the boreal forest contains more forested land than all tropical forests combined. It stretches from Newfoundland and Labrador in the east across Canada and Alaska (North American taiga, approximately 5.5 million km²), and from Scandinavia across Russia’s Ural Mountains, Siberia, and the Russian Far East to Kamchatka (Eurasian taiga, approximately 9 million km²) — a nearly unbroken forest of spruce, fir, pine, and larch covering a sixth of all land on Earth.

The ecological structure of the boreal forest is shaped by the dominance of conifers — spruce (Picea glauca, P. mariana), fir (Abies balsamea), pine (Pinus banksiana, P. sylvestris, P. sibirica), and the exceptional larch (Larix sibirica, L. gmelinii) — the only deciduous conifer, which sheds its needles in autumn. Conifers dominate the boreal for several interconnected reasons: their needle-like leaves have thick cuticles and a compact geometry that resists desiccation during winter when water is frozen and physiologically unavailable (winter drought); their narrow, conical crowns shed heavy snow loads and do not break under the weight; their dark needles absorb heat rapidly in spring, allowing photosynthesis to resume at low temperatures; and their shallow root systems spread laterally rather than deeply, allowing them to access nutrients in the thin, poorly developed soil above the permafrost. Below-ground, ectomycorrhizal fungi connect conifer roots to an extensive nutrient-scavenging network — critical in the nutrient-poor podzol soils that boreal climate and conifers’ acid needle litter create together.

Tundra — the Biome at the Climate Frontier

The tundra biome — from the Finnish word tunturi (treeless plain) — encircles the Arctic Ocean in a belt approximately 3,000 km wide, covering approximately 8–11 million km² of Canada, Alaska, Russia, Scandinavia, and Greenland. An analogous alpine tundra occurs at high altitudes above the treeline on every major mountain range worldwide — the Tibetan Plateau, Andes, Rocky Mountains, and Alps all contain substantial alpine tundra. The defining constraint of tundra is the combination of low temperatures (mean annual temperatures typically −10°C to −20°C), short growing seasons (6–10 weeks), permanently frozen subsoil (permafrost, sometimes extending 600 m deep), and low precipitation (100–400 mm/yr — technically desert levels, but evaporation is also very low, so water stress is not the primary constraint).

Freshwater Biomes — Lakes, Rivers, Wetlands, and Their Extraordinary Diversity

Freshwater biomes cover less than 1% of Earth’s surface but harbour approximately 10% of all described species and one third of all vertebrate species — a staggering concentration of biodiversity relative to their area. Freshwater systems are the planet’s most threatened biome type: freshwater species have declined by an average of 84% since 1970 (Living Planet Index — freshwater), a rate of decline nearly twice that of terrestrial or marine species. This crisis reflects the intersection of every major environmental pressure — damming and flow alteration, water extraction, pollution, invasive species, and climate change — in the biome least able to buffer or escape these impacts.

Marine Biomes — Ocean, Coral Reef, Estuary, and Kelp Forest

Marine biomes cover approximately 71% of Earth’s surface — more than all terrestrial biomes combined — and regulate the global climate system in ways no terrestrial biome can match. The world’s oceans absorb approximately 26% of all anthropogenic CO₂ emissions and approximately 90% of the excess heat generated by the enhanced greenhouse effect. They generate over half of Earth’s oxygen through marine phytoplankton photosynthesis. They cycle nutrients, water, and energy at planetary scale through ocean circulation systems (thermohaline circulation, gyres, upwellings) that connect every ocean basin and interact with atmospheric circulation. The diversity of marine life encompasses the entire evolutionary tree of life — all major animal phyla are represented in the ocean, while only approximately 14% of animal phyla have colonised land.

Coral reef ecosystems — the marine equivalent of tropical rainforests in terms of biodiversity concentration — cover less than 0.1% of the ocean floor yet support approximately 25% of all known marine species. Constructed by the calcium carbonate skeletons of reef-building (scleractinian) corals and calcareous algae, reefs create three-dimensional habitat structure of extraordinary complexity in otherwise nutrient-poor tropical seas. The apparent paradox of coral reefs — extraordinary biodiversity and productivity in nutrient-poor tropical oceans (the “desert sea” surrounding them) — is resolved by the coral-zooxanthellae symbiosis: unicellular photosynthetic dinoflagellates (Symbiodiniaceae, the zooxanthellae) living in coral tissues provide up to 90% of the coral’s energy needs through photosynthesis, enabling the coral to calcify rapidly and build reef structure, while the coral provides the zooxanthellae with shelter and nutrients. This symbiosis is the foundation of reef ecosystem function — and its disruption by ocean warming (bleaching, where corals expel their zooxanthellae when heat stress is sustained) is the primary mechanism by which climate change is destroying reef systems globally.

Ecosystem Services Across Biomes — What Nature Provides to People

Threats to Biomes — Deforestation, Conversion, Pollution, and Climate Change

Every major biome on Earth faces one or more existential or functional threats driven by human activity. The scale, rate, and irreversibility of these threats have accelerated dramatically since 1950, and particularly since 1990. The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) 2019 Global Assessment concluded that the current rate of species extinction is between 10 and 100 times higher than the natural background rate — with habitat loss and degradation in biomes identified as the primary driver. Understanding biome threats is not merely academic — it is the precondition for any effective conservation response.

Biodiversity Hotspots, Conservation, and the 30×30 Goal

The biodiversity hotspot concept, introduced by Norman Myers in 1988 and operationalised by Conservation International, identifies regions of exceptional biodiversity concentration combined with exceptional habitat loss — the places where conservation effort is most urgently needed and where the return on investment is potentially highest. A region qualifies as a biodiversity hotspot if it contains at least 1,500 endemic vascular plant species (>0.5% of the world’s total) AND has lost at least 70% of its original natural vegetation. As of the most recent assessment, 36 biodiversity hotspots have been identified, together covering just 2.4% of Earth’s land surface but containing over 50% of the world’s plant species and approximately 43% of bird, mammal, reptile, and amphibian species as endemics found nowhere else.

Climate-Driven Biome Shifts — the Future Geography of Life

Earth’s biomes are not static. On geological timescales, biome boundaries have shifted in response to glacial-interglacial cycles — during the Last Glacial Maximum (21,000 years ago), most of Canada and northern Europe were under ice sheets, boreal forest occupied what is now temperate grassland in the USA, and tropical rainforests were apparently reduced to refugia in the Congo Basin, western Amazonia, and Southeast Asia. The difference between natural glacial-interglacial biome shifts and the current human-induced change is not the magnitude of shift, but the rate: natural glacial cycles operate over tens of thousands of years; current warming is occurring over decades — potentially faster than species can migrate, adapt, or evolve.

Biome boundary projections for 2050–2100 under moderate (RCP4.5) to high (RCP8.5) emission scenarios suggest: approximately 30–40% of existing biome area will be subjected to conditions outside the historical climate envelope of that biome type; the boreal forest-tundra boundary will shift northward by approximately 5°N by 2100 under RCP8.5 — 500 km northward displacement in less than 80 years, compared to approximately 10 km/century during the Holocene; the southern boundary of the boreal is likely to transition toward temperate broadleaved or drier woodland; the tropical rainforest biome faces expansion of its climate envelope into currently savanna-occupied latitudes (where cleared land would permit rainforest establishment if deforestation pressure is reduced) and contraction of its envelope in the eastern Amazon (where reduced rainfall and increased drought frequency already drive forest degradation). The NASA Earth Observatory’s global vegetation and land use maps document ongoing changes in vegetation cover, providing satellite-based evidence of biome boundary shifts already occurring.

A particularly important concept in climate-biome interaction is the potential for tipping points — thresholds beyond which a biome can shift abruptly to an alternative stable state without further forcing, and from which recovery is extremely difficult even if the original forcing is removed. The most studied potential tipping element is the Amazon rainforest: a combination of deforestation (currently ~18–20% of original cover lost) and warming-driven drought stress may push the Amazon system past a threshold (estimated at ~20–25% deforestation under current climate, possibly lower under increased drought) beyond which regional evapotranspiration decreases enough to reduce regional rainfall, further stressing the forest — a positive feedback (the “forest-rainfall feedback”) that could convert 30–60% of the Amazon to savanna without any additional human clearing. This savanification would release 50–100 billion tonnes of carbon, fundamentally restructure the South American hydrological cycle, and destroy irreplaceable biodiversity within decades — not centuries.

Frequently Asked Questions About Biomes of the World