Biomes are large regions of the world that share similar climate, soil, plants, and animals. Think of them as the planet’s major habitat types: tropical rainforests, deserts, tundra, grasslands, and oceans are all biomes. They operate on a much larger scale than a single ecosystem or habitat, and a single biome can contain many different ecosystems within it. Understanding biomes is really about understanding how climate shapes life on Earth.
Biomes vs. Ecosystems vs. Habitats
These three terms describe nature at different zoom levels. A habitat is the specific area where a particular species lives, like a rotting log for beetles or a coral head for a clownfish. An ecosystem is broader: it describes how plants, animals, and their environment interact in a given area, with a focus on how nutrients and energy flow between them. A pond is an ecosystem. A patch of forest is an ecosystem.
A biome sits above both of these. It groups together all the places on Earth that share similar climate conditions and, as a result, similar types of life. The Amazon rainforest and the rainforests of Borneo are thousands of miles apart, but they belong to the same biome because they share high rainfall, warm temperatures, and extraordinary biodiversity. Within that single biome, there are countless individual ecosystems and habitats.
The Major Terrestrial Biomes
Scientists generally recognize several broad terrestrial biomes, though exact classifications vary. The main ones include tropical rainforest, temperate forest, boreal forest (taiga), grassland and savanna, desert, and tundra. Each is defined primarily by its temperature range and annual precipitation, which together determine what can grow there and, by extension, what animals can survive.
Tropical Rainforest
Tropical rainforests are the most biodiverse biome on Earth. They receive between 200 and 300 centimeters (roughly 6.5 to 10 feet) of rain per year, and daytime temperatures hover around 29°C (85°F) year-round with only about a 5°C seasonal swing. That constant warmth and moisture supports an extraordinary density of life. Humid tropical forests harbor more than 90% of all tropical forest vertebrates, and up to 29% of global vertebrate species are found nowhere else.
One counterintuitive fact: rainforest soils are nutrient-poor. Heavy rains wash organic material out of the soil quickly. The forest sustains itself through rapid recycling. Bacteria, fungi, and other decomposers break down fallen leaves and dead organisms so fast that plants absorb nutrients almost immediately, before they can accumulate in the soil. This is why cleared rainforest land often makes poor farmland after just a few seasons.
Desert
Deserts are defined by dryness, not heat. Any region receiving less than about 250 millimeters (10 inches) of precipitation per year qualifies. That includes scorching places like the Sahara and surprisingly cold ones like parts of Antarctica. Plants and animals in deserts have evolved dramatic water-conservation strategies: waxy coatings on leaves, nocturnal activity patterns, and the ability to go long periods without drinking.
Tundra
The tundra is Earth’s coldest biome, with temperatures ranging from -40°C to about 18°C during brief summers. It receives just 150 to 250 millimeters of precipitation per year, including melted snow, which is actually less than most of the world’s driest deserts. The defining feature is permafrost, a layer of permanently frozen ground beneath the surface. During summer, only the top few inches of soil thaw, creating a thin growing surface for shallow-rooted plants like mosses, lichens, and low shrubs. Trees can’t establish roots in permafrost, which is why the tundra looks so open and barren.
Temperate and Boreal Forests
Temperate forests experience four distinct seasons and moderate rainfall, supporting broadleaf trees like oaks and maples that shed their leaves in autumn. Farther north, boreal forests (also called taiga) are dominated by cold-hardy conifers like spruce and pine. The boreal forest forms an enormous band across Canada, Scandinavia, and Russia, making it one of the largest biomes by land area.
Grasslands and Savannas
Grasslands receive enough rain to support grasses but not enough to sustain dense tree cover. Temperate grasslands, like the North American prairies and the Eurasian steppe, have hot summers and cold winters. Tropical grasslands, called savannas, stay warm year-round and are dotted with scattered trees. Both types are shaped heavily by fire and grazing, which prevent forests from taking over.
Aquatic Biomes
Water-based biomes cover more of the planet than land-based ones and are divided into freshwater and marine categories. Freshwater systems include flowing water like rivers and streams (called lotic systems) and still water like lakes, ponds, and wetlands (called lentic systems). Each supports different communities of life. A fast-moving mountain stream and a still, warm pond are both freshwater environments, but the organisms that thrive in each are very different.
Marine biomes include the open ocean, coral reefs, estuaries (where rivers meet the sea), and deep-sea environments. Coral reefs, sometimes called the rainforests of the sea, rival tropical forests in biodiversity despite covering a tiny fraction of ocean area. The open ocean, by contrast, is vast but relatively sparse in life per unit of water, with most activity concentrated near the surface where sunlight penetrates.
How Scientists Classify Biomes
There is no single universal system for dividing the world into biomes. Different ecologists draw the boundaries differently depending on which variables they prioritize. One well-known framework, the Holdridge Life Zone system, classifies regions using three climate measurements: annual precipitation, biotemperature (a measure of warmth during the growing season), and the ratio of evaporation to precipitation. Other systems rely more heavily on vegetation type or soil characteristics.
This is why you’ll see different numbers in different sources. Some list five biomes, others list eight or twelve. The underlying reality is a gradient: biomes blend into each other at their edges rather than stopping at sharp lines. The transition zone between forest and grassland, for example, can stretch for hundreds of miles.
How Human Activity Is Reshaping Biomes
More than three quarters of Earth’s ice-free land surface is now covered by what some ecologists call anthromes, or anthropogenic biomes. These are landscapes shaped primarily by human activity: croplands, rangelands, dense settlements, and villages. The remaining wildlands untransformed by agriculture and settlement cover a shrinking fraction of the planet. In practical terms, most of the land you see in the world today no longer fits neatly into its “natural” biome category.
Climate change is adding another layer of disruption. As temperatures and rainfall patterns shift, biome boundaries are moving. Research published in Nature estimates that by 2050, 10% to 47% of Amazonian forests could face compounding disturbances severe enough to trigger unexpected ecosystem transitions. That means portions of the world’s largest tropical rainforest could shift toward savanna-like conditions within decades. Similar boundary shifts are happening in boreal forests, where warming is pushing the tree line northward into former tundra, and in arid regions, where desertification is expanding grasslands into shrublands.
These shifts matter because biomes anchor regional weather patterns, store carbon, cycle water, and support the food webs that human economies depend on. When a biome changes, the services it provides change too, often in ways that cascade far beyond the region itself.