Peat bog, Sumava National Park, Czech Republic
The peat bog in Sumava National Park in the Czech Republic, supports a diverse ecosystem. Photo: © K. Stuchelova

9 Major Biomes of the World

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This article explains the 9 most important land biomes on Planet Earth, outlining each area’s climate, soil and biodiversity of animal and plant species. It also looks at the impact of global warming on each biome. We begin with a short outline of how Earth’s biosphere is classified and a brief explanation of the components that make up its structure.

The Biosphere

The biosphere is divided into a hierarchy of vaguely defined geographical regions, according to size. The largest of these is the “biogeographical realm” or “ecozone”. According to the WWF classification, these are 8 of these realms. 1 2

Map of the 6 Main Biogeographical Realms
Map showing 6 of the 8 Main Biogeographical Realms (Ecozones). Green = Nearctic; red = Palearctic; purple = Neotropic; blue = Afrotropic; brown = Indomalaya; orange = Australasia. Not shown are the Antarctic Realm and the Oceania Realm (contains no continental land mass but includes Polynesia, Micronesia, and the Fijian Islands). Image: © Carol (CC BY-SA 3.0)

The 8 Biogeographical Realms

  • Palearctic (54m sq km) – most of Eurasia and North Africa.
  • Nearctic (22.9m sq km) – most of North America.
  • Afrotropic (22m sq km) – Trans-Saharan Africa and Arabia.
  • Neotropic (19m sq km) – most of South America, Central America, and the Caribbean.
  • Australasia (7m sq km) – Australia, New Guinea, New Zealand, and neighbouring islands.
  • Indomalaya (7.5m sq km) – Indian subcontinent, Southeast Asia, southern China.
  • Oceania (1m sq km) – Polynesia, Micronesia, the Fijian Islands.
  • Antarctic (14m sq km) – Antarctica.

Next in size after biogeographical realms, are “bioregions”, followed by “ecoregions” which are often interchangeable with “biomes”.

What Are Biomes?

Biomes are ecological zones with distinct collections of plants and animals, that have formed because they share the same climate – the same temperature, amount of rainfall and humidity. 3 The biome is the basic unit of the ecological system. It’s the only unit that is small enough to be distinct, but large enough to matter. A biome covers a wider physical area than an ecosystem or habitat: a biome may consist of hundreds of ecosystems, and a great many habitats.

There is no set number of biomes, and there are no fixed boundaries between biomes. For example, the Brazilian Pantanal biome (aquatic) only gradually gives way to the drier, denser vegetation of the Amazon rainforest biome (terrestrial). A desert biome will gradually become less arid and less barren as it gives way to dry shrubland, before finally changing into grassland.

Because biomes are largely shaped by climate, if the climate changes so does the biome. A major concern of climate science, is the possible savannization of the Amazon Rainforest, whereby the humid rainforest biome gradually dries out and turns into grassland.

An earlier example of biome-change occurred at the end of the Stone Age, when parts of North Africa consisted of lush tropical vegetation, with abundant rivers and streams as well as large mammals, such as giraffes, rhinos, hippos, and crocodiles. Since then, this lush savanna has completely changed, and is now part of the arid Sahara Desert.

What Are Anthropogenic Biomes?
Anthromes (Anthropogenic Biomes, or “human biomes”) represent ecological patterns created by sustained direct human interactions with ecosystems. 4

What is a Microbiome?
A microbiome describes the complex communities of microbes (bacteria, archaea, protists, fungi, protozoa and viruses) that inhabit very small environments, such as the human body (or the human digestive system), the bodies of specific animals, an individual tree, and so on.

What is Biota?
The ‘biota’ of a biome, ecosystem or habitat, is just a fancy way of saying ‘the area’s total collection of animal and plant species, as well as microbial communities’. There are marine biotas (pelegic, benthic or coastal, depending on whether its deep ocean, sea-bed or continental shelf/coast), aquatic biotas, and terrestrial biotas.

Biotic versus abiotic
The word ‘biotic’ is another buzzword. It simply means ‘living’. Likewise, abiotic means non-living. For example, Planet Earth contains biotic components, such as green plants, whose photosynthesis keeps all of us alive. But photosynthesis requires the presence of three abiotic elements: sunshine, carbon dioxide and water.

What Are Ecosystems?

The term ecosystem is a bit vague, because we can speak of the ecosystem of a pond (small), or the ecosystem of the Antarctic (huge). Basically, an ecosystem is the systematic interaction of a set of living beings (animals, plants, and other tiny organisms) within a particular habitat.

Interdependence is a key feature of an ecosystem and its food web. Animals depend upon other animals as well as plants, for food, while plants rely upon animals (especially birds) to spread their seeds and pollen, so that new plants can take root and grow.

What’s The Difference Between a Biome and an Ecosystem?

The word ‘biome’ describes a relatively large ‘geographical zone’ from the point of view of its climate and its distinct biological life (biota) – that is, its collection of animals and plants. The same biome (e.g. tropical rainforest) may reoccur in several other locations around the world that share a similar climate and other biogeographical conditions. Examples of biomes include: tundra, temperate forests, deserts, and grasslands.

By contrast, the word ‘ecosystem’ really describes a ‘system’ – a system of interaction between the living (biotic) and non-living (abiotic) components of an area. Typical interactions include: how animals relate to each other in the food chain (who eats who), and how they relate to other non-living (abiotic) components (water, temperature, salinity etc). Areas that we usually speak of as having their own ecosystem include: ponds, meadows, forest canopies, beaches, peat bogs, woodland, desert sands, coral reefs, along with hundreds of others. 5

If you want a very crude analogy: a biome’s relationship to an ecosystem, is like a state’s relationship to society.

Why Are Biomes Important?

According to conservationists, biomes and other eco-regions are important because they encompass areas with important ecological and evolutionary processes and conditions. Sometimes they contain endangered species of animals or plants whose loss would be irreplaceable. And although tropical rainforests and coral reefs harbor the most biodiversity, unique manifestations of nature can be found in all other biomes, which may be lost forever if they are not safeguarded and conserved. 6

Map of the main biomes in the world
World map showing main terrestrial biomes. Image: © Internet Geography. 7

The 9 Most Important Biomes

We profile nine biomes: ice cap, tundra, taiga, temperate forest, tropical rainforest, grassland, savanna, desert, and freshwater (lakes, rivers and wetlands). 8

1. Polar Ice Cap Biome

Jakobshavn Glacier, Satellite Image
Jakobshavn Glacier in western Greenland is notorious for being the world’s fastest-moving glacier. It discharges a huge amount of ice (sea ice) into the Disko Bay area, which has implications for rising sea levels. Photo: © NASA Satellite image, June 2019.

An ice cap is a covering of ice over a large area of land – usually less than 50,000 sq km. Larger ice caps are known as ice sheets, of which there are two in the world – one covering Antarctica, the other covering Greenland. All ice environments form part of the cryosphere, the sub-system of Planet Earth that consists of solid water. The main function of the cryosphere is to help regulate Earth’s climate system by absorbing heat from the equator and distributing cold water around the world, via deep-water currents.


The two main areas with ice cap climates are Greenland and Antarctica, both of which have vast deserts of snow and ice. The Greenland ice sheet occupies an area of 1,710,000 square kilometres (660,000 sq mi). This excludes its coastline, which is tundra. By comparison the Antarctic ice sheet covers an area of 14 million square kilometres (5.4 million sq mi).

In addition, a large portion of the Arctic Ocean near the North Pole remains frozen 365 days of the year, which in practice gives it an ice cap climate. 9


The ice cap climate is famous for its freezing polar conditions in which no mean monthly temperature exceeds 0 °C (32 °F). During the coldest months, mean temperatures range between minus 30 and minus 55 °C (minus 22 to minus 67 °F). The biome’s low temperature is mainly due to the angle of the Sun, which is very low in the sky, forcing the sun’s energy to pass through more atmosphere. This means the sunlight that reaches the surface contains less energy than at the equator. Much of the sunlight is also reflected back into space.

The Arctic used to be noted for long, cold winters and short, cool summers, although this is changing due to rising temperatures throughout the region. Precipitation is low, no more than 200mm (7.5 in) per year, mostly in the form of snow. Some of the Arctic is covered by ice (sea ice or glacial ice) all year-round, with nearly all areas undergoing long periods with some form of ice on the ground.

The Greenland ice sheet is between 2 km (1.2 mi) and 3 km (1.9 mi) thick. However, due to the amount of ocean water in the circumpolar region (whose temperature can never fall below −2 °C /28 °F), the Arctic is significantly warmer than Antarctica, which is a continental land mass. 10

Antarctica is really like a cold desert, due to its low level of precipitation (166 mm/ 6.5 in), which is exclusively snow. In coastal regions, it rises to about 200 mm. It is noted above all for its extreme cold, especially in higher areas where temperatures typically decrease 1°C for every 100 m increase in height. It’s worth noting that Antarctica is the world’s highest continent, with an average land height of 2,300 meters (7,475 feet). Its cold is also exacerbated by its high albedo, which reflects most sunlight back into space. The continent also experiences hurricane force winds, up to 200 mph.

Antarctic ice averages 2.5 km in thickness and can go up to 5 km deep. Antarctica contains 90 percent of the world’s stock of ice and more than 70 percent of its freshwater. Much of the ground underneath the ice is below sea level, but this is due not to its lack of elevation but rather the weight of the ice itself. If the ice were to melt, the ground would rise back up again.

During the winter months, the waters of the Southern Ocean surrounding Antarctica, turns to ice. This sea ice nearly doubles the size of the continent.


Ice caps are usually covered by a permanent layer of ice and therefore have no trees, plants or shrubs to speak of, and very few flowering plants.


There is some limited animal life (e.g. polar bears) on the ice cap, usually found near the ocean edges where seals breed. The polar climate is very inhospitable to humans, although a number of scientific research stations are located in both Greenland and Antarctica, such as the facilities operated by the British Antarctic Survey.

Antarctic Food Web
The Marine Food Web of the Antarctic showing phytoplankton, the primary producer, at the base, with zooplankton and krill as the main feedstock for most other creatures.

The main exception to the lack of animals is Antarctica’s penguin kingdom that comes ashore to breed in their millions. However, although they breed on land, their energy and food come from the Southern Ocean, so they are classified as part of the marine ecosystem.

The Southern Ocean is exceedingly rich in life, due in part to the upwellings of the deep-water thermohaline circulation, bringing nutrition up from the depths. Although phytoplankton are seen now in the Arctic, far more of these marine drifters are found in the Southern Ocean, where they serve as food for krill who occupy the trophic level above them in the marine food chain. Krill in turn feed whales and many other species. Returning to the penguins, these creatures are an important food source for leopard seals and killer whales.

Effects of Climate Change on Ice Cap Biome

Arctic sea ice is melting rapidly, as is the ice sheet in Greenland. This is due to record air temperatures in the Northern Hemisphere. Antarctica, too, is experiencing record-breaking temperatures which, together with shifting wind patterns, are believed to be causing rapid melting of ice in both West and East Antarctica. 11 These rising temperatures are the result of heat-trapping gases from fossil fuel combustion adding to the greenhouse effect in the lower atmosphere. The main danger from warmer polar biomes is the sea level rise caused by the melting of land ice, especially in Antarctica.

2. Tundra Biome

Alpine Tundra, National Park, Canada
Alpine tundra is found at high elevations, such as Lake Clark National Park and Preserve, Canada. This tundra is home to a host of vibrant but fragile plant life (including blueberries and cranberries) and animal species such as the reindeer. Photo: © NPS/L.Wilcox

The word tundra comes from the Finnish word ‘tunturi’, meaning ‘treeless plain.’ The tundra biome is best known for its cold, driving winds and cold temperatures. It’s also noted for its sub-surface store of permanently frozen soil, or ‘permafrost’, which prevents the growth of trees and most other shrubs, giving tundra its distinctive barren and windswept appearance.


Nearly all tundra is found in the Northern Hemisphere, although some tracts occur in the Antarctic, and in high altitude Alpine areas around the world. In total it is thought to cover up to 20 percent of the Earth’s land surface, although estimates vary according to different interpretations of the tundra biome.

NOTE: Permafrost contains soil, silt, sand, gravel, clay, and small particles of rock, all bound together by frozen water (ice). Upper layers usually contain large amounts of semi-decomposed vegetation and animal material. Lower levels contain soils made up mostly of minerals. The layer of earth that sits on top of the permafrost – only 15 centimeters (6 inches) thick in colder areas, several meters thick in warmer areas – only freezes during the cold winter months but thaws during the spring and summer. Permafrost constitutes one of Earth’s largest reservoirs of carbon. Were it to thaw, an enormous amount of carbon dioxide would enter the atmosphere.

In the Northern Hemisphere, tundra is found in the Arctic north of the boreal forest or taiga belt along the circumpolar coasts of Alaska, Canada and Siberia.

In the Southern Hemisphere, it occurs on the Antarctic Peninsula as well as on several outlying islands, including South Georgia, the South Sandwich Islands and the Kerguelen Islands. It is also found on the Auckland Islands, Antipodes Islands, Bounty Islands, and Campbell Islands of New Zealand, and Macquarie Island of Australia.

Alpine tundra occurs above the timberline on high altitude mountain summits, slopes, and ridges in ecoregions around the world. For example, in the North American Cordillera, the Andes of South America, the Alps and Pyrenees of Europe, the Eastern Rift mountains of Africa, and the Himalayas and Qinghai-Tibetan Plateau in Asia.


The Tundra biome is characterized by extremely low temperatures and little rainfall (less than 250mm/ 10 inches annually). Winters are long with January temperatures averaging from minus 20° to minus 30°C (minus 4° to minus 22°F). Summers are short (6-12 weeks). Until the 1990s, summer temperatures rarely exceeded 50°F (10°C), with just enough heat to thaw the surface of the ground. Today, in some parts of the Arctic at least, temperatures have risen by 3-4°C (5.4 to 7.2°F). Scientists have calculated they are higher now than they have been for 44,000 years, perhaps even for 120,000 years. 12 As a result, in some areas, the surface rarely freezes even in winter and remains soggy all year from melted snow and rain.


The soil of the tundra biome typically lacks nitrogen and phosphorus – two important elements for plant growth. Plants therefore tend to be small or stunted and makes growth is slow. Most plants reproduce by budding and division rather than flowering. Also, the growing season tends to be short, lasting about 60 days. All tundra plants have adapted to driving winds and group together to help each other resist the cold temperatures. They have also adapted so that they need only a small amount of water to germinate and grow, and in addition, have developed the ability to perform photosynthesis at low temperatures and in low light.

For more about important chemicals in the soil, please see our articles on: The Nitrogen Cycle and The Phosphorus Cycle.

In total, there are roughly 1,700 plant species in the Arctic and Subarctic tundra biome and around 400 types of flowers. They include: arctic moss, Moss Campion, Caribou moss, crustose and foliose lichens, saxifrage, liverworts, willow shrubs and other small plants. Grasses include cotton grass and Alpine Blue grass. Tundra flowers include Bearberry, marsh marigold, Pasque flower and Labrador Tea flower. Alpine tundra plants also include tussock grasses, dwarf trees, small-leafed shrubs, and meadow plants.


The apex predator of the tundra is the polar bear, whose food sources include summer berries and eggs, as well as seals, walruses, and trapped beluga whales. Other predators, like wolves and foxes, survive on caribou, lemmings, voles, and arctic hares. At the bottom of the food web, insects, such as moths, grasshoppers, mosquitoes, and other flies, provide food for migratory birds, including: snow buntings, loons, sandpipers, snow birds, terns and several species of gulls. In the warmer Alpine tundra biome, animals include elk, mountain goats, sheep, pikas and marmots, as well as insects like grasshoppers, butterflies, springtails and beetles.

Effects of Climate Change on Tundra Biome

One of the biggest effects of global warming on Tundra is permafrost thaw caused by the abnormally high temperatures. Scientists calculate that the amount of carbon locked into the permafrost is about twice that in the atmosphere. Which means that if permafrost thaw ever reached a tipping point and became irreversible, temperatures would skyrocket. 13

3. Taiga Biome (Boreal Forest)

Taiga, known in Canada and Alaska as boreal forest, is the largest land biome on the planet and is famous for its coniferous forests consisting mostly of pines, spruces, and larches. 14

Boreal Forest Alaska
Boreal forest, Alaska. There is little rainfall in the boreal biome. Precipitation comes in the form of fog and snow, with a little rain during the summer months. Photo: © Fredrik Norsell


It is found in a band around the Northern Hemisphere sandwiched between the tundra in the north and either temperate grassland or deciduous forest in the south. It covers about 17 million square kilometres (6.6 million square miles) of the Earth’s land area. 15

It covers most of inland Canada, Alaska, and parts of the northern United States. In Europe, taiga covers part of the Scottish Highlands; the coastal areas of Iceland; much of Norway; most of Sweden and Finland; a swathe of Russia (including a vast area of Siberia) all the way from Karelia in the west to the Pacific Ocean in the East; plus northern Kazakhstan, northern Mongolia, and northern Japan. In addition, it is found at high altitudes in the more temperate latitudes, such as the mountainous western area of North America.

Tree species and summer temperatures vary, however. For example, the boreal forests of North America contain mostly spruces; the Scandinavian taiga comprises a mixture of pines, spruce, and birch trees, the same as the Russian taiga, while the Eastern Siberian forests are mainly larch.


The taiga biome can be colder as well as warmer and wetter than tundra. Generally, taiga forests experience long, cold winters (8-10 months), and short, mild, humid summers (typically 1-3 months but never more than 4 months). Winter days are short and very cold. The lowest recorded temperatures in the Northern Hemisphere were recorded in the Siberian taiga.

In general, the taiga has a subarctic climate with large seasonal variations in temperature. At its coldest, winter averages between −6 °C (21 °F) and −50 °C (−58 °F), while summer averages 10 °C (50 °F) or higher. Like the tundra, taiga also has permafrost in parts. Discontinuous permafrost is seen in areas with average temperatures below freezing (0 °C; 32 °F). Within the Arctic Circle, there is midnight sun in mid-summer.

In the south and west of the Eurasian taiga, the summers are warm and wet and last longer, while average annual temperatures are higher, sometimes merging into those of the deciduous forest or grassland biomes.

Fires are a relatively common occurrence in the taiga during the summer. They help the biome to regenerate by consuming dead wood and biomass, clearing out the tree canopies, and making room for new growth, which sunlight can now invigorate on the forest floor.

Precipitation in the taiga ecozone is relatively low throughout the year. Annual rainfall equivalent is 200–750 mm (8-30 inches), mostly as rain during the summer, but snow in winter. The ground may remain carpeted with snow for as long as nine months in the northernmost areas.

The growing season, when flowers and plants come alive, is between 80 and 150 days except in the extreme north where it averages 50-70 days, and in coastal areas of Scandinavia and Finland where it averages 145-180 days.


Soils in the taiga are usually quite thin and nutrient-poor due to the cold, which stunts all metabolic development. The soil is acidic because of acids from falling evergreen pine needles, so the forest floor has only lichens and mosses growing on it, with few fungi to speed up decomposition and enrich the soil with organic content, as in deciduous forests.


The taiga has a low diversity of plant life. Conifers (cone-bearing evergreen trees with needles) are the most prevalent type of tree. The thin needles with their waxy coating reduce water loss of the conifer through transpiration, and thus compensate for the difficulty in obtaining water from the frozen winter ground. But desiccation remains a problem. The design of the conifer’s waxed needles also allows snow to slide off rather than snap branches with its weight.

Conifer species include pines, firs, spruces and larches. Occasionally deciduous species are present, including birch, oak, aspen, poplar, willow and rowan. The southernmost extremities of the taiga may have trees such as maple, elm and lime scattered among the conifers, and there is sometimes a transition into a temperate mixed forest, as in eastern Canada.

The tree mix varies with climate and geography, so for example, in Scandinavia and western Russia, the Scots pine is a widespread species, while in the Eastern Canadian forests in the Laurentian Mountains and the northern Appalachian Mountains balsam firs dominate, while further north in the taiga of northern Quebec and Labrador, black spruce and tamarack larch are common.


The boreal forest supports a reasonably limited diversity of animals due to the harshness of the climate. Canada’s forests include 85 species of mammals, more than 100 species of fish, and around 32,000 species of insects. Insects play a vital role within the taiga ecosystem as pollinators, decomposers, and trophic levels within the food web. Many birds depend upon them for food during the summer months.

The taiga is a challenging biome for reptiles and amphibians, who depend on environmental conditions to regulate their body temperatures. The few species in the boreal forest include the common European adder, blue-spotted salamander, red-sided garter snake, northern two-lined salamander, Siberian salamander, wood frog, American and Canadian toads. Most hibernate underground in winter.

Fish in the freshwater ecosystems of the taiga must be able to adapt to life under ice-covered water. Species include northern pike, walleye, Alaska blackfish, white sucker, lake whitefish, pygmy whitefish, Arctic lamprey, several species of grayling, brook trout, chum salmon, and Siberian lake chub.

Several large herbivorous mammals can be found in the taiga, including the wood bison, which is native to northern Canada, and Alaska, and has been recently introduced into the Russian Far-East. Other herbivores include moose, reindeer and caribou. Some areas of the more southern taiga also contain elk (wapiti) and roe deer.

Smaller mammals include beaver, squirrel, porcupine, vole, ermine and moles, as well as the snowshoe and mountain hares. Some larger mammals, such as bears, eat heavily during the summer in order to gain weight. Then they hibernate during the winter.

Predatory mammals of the taiga include grizzly bears, wolves, lynx, stoat, weasel, sable, river otter, mink, wolverine, red fox, brown bear, American black bear, Asiatic black bear, and Siberian tiger.

Over 300 species of birds nest in the taiga, taking full advantage of the long summer days and abundance of insects found around the numerous bogs and ponds. Of these species only 30 remain for the winter. These either feed on carcasses or prey on live mammals. Species include, golden eagles, rough-legged buzzards, ravens, grouse and crossbills.

Effects of Climate Change on Taiga Biome

In 2019, Arctic wildfires in Siberia and northern parts of Russia destroyed 43,000 square kilometres (17,000 sq mi) of taiga. In Canada, 18,000 square km were lost, while in Alaska 9,700 square kilometres were destroyed. The Siberian fires alone released carbon emissions equivalent to Sweden’s entire annual output of greenhouse gases, and resulted in a cloud of smoke greater than the entire surface area of the EU. For more on the subject of wood combustion, see: What is the Effect of Wood Burning on Climate Change?

4. Temperate Forest Biome

Colourful Temperate Forest in Europe
Temperate forests have a moderate climate and precipitation is generally distributed evenly throughout the year. The canopy of a temperate forest consists mainly of broad-leaved trees. As you move closer to the polar regions, temperate forests give way to boreal forests. See also: 7 Effects of Climate Change on Plants and Trees. Photo © Brian Lawrence

Temperate forests consist of a wide mixture of deciduous broad-leaved trees that shed their leaves in autumn. 16 A mild climate combined with a rich diversity of plants, provides abundant food and habitats for a wide range of animals, birds and insects.


Most temperate forests are found between 40-60° north and south of the equator. Some of the best examples are the deciduous forests of eastern North America, Southern Europe, Central China and Russia’s Far East.


The climate of the temperate broadleaf forest biome is characterized by plentiful all year-round rainfall (up to 1500mm, 60 inches, annually), along with mild temperatures around 3-16 °C (37-60 °F), at least in the mid-latitudes. The biome has four well-defined seasons, caused by the tilt of the Earth’s axis. During the year, the sun’s rays strike different parts of the world more directly than others, resulting in varying temperatures, or seasons. In the temperate forest biome, this leads to warm summers and cool winters, although conditions vary somewhat around the world. For example, the southern edge of the zone tends to be more humid throughout the year.

Deciduous Trees

Deciduous trees, the dominant trees in temperate woodlands, have leaves rather than pine needles, and they change with the seasons. In the summer their broad green leaves absorb sunlight which they turn into energy via the process of photosynthesis. As temperatures fall during the autumn, the green pigment in their leaves (chlorophyll) breaks down, revealing the brilliant oranges, reds and yellows, that we see at this time of the year. In winter, deciduous trees and plants enter a sort of stand-by state – it’s too cold for them to prevent their leaves from freezing, so they simply shed them, and seal the spots where leaves were attached, with a protective cover. With the advent of warmer spring temperatures, they grow new leaves, and the cycle restarts.

Forest Structure

Temperate deciduous forests typically have a 4-layer structure. The topmost layer is the ‘canopy’, consisting of tall mature trees standing 30-61m (100-200 ft) high (like oaks).

Below the canopy are three layers that make up the ‘understory’, standing about 9-15m (30-50 ft) shorter than the canopy. The upper section consists of shorter mature trees (like maples), saplings, and juvenile canopy layer trees awaiting an opening in the canopy, through which to rise. Next comes the shrub layer, consisting of low woody plants (mountain laurel, huckleberries, azaleas, hydrangeas, pussywillow, Japanese barberry, wayfaring tree, Russian almond, and tons more). Finally, there is the ground cover or herbaceous layer – the layer with the most variety (ferns, lichens and mosses).

In the Northern hemisphere, the tallest broadleaf trees include oaks, beeches, or birches. Coniferous trees, whose presence in the canopy earns the forest its ‘mixed’ status, include firs, pines, and spruces. In some parts of the North, conifers may actually be more dominant than the broadleaf species, as the taiga and the temperate deciduous forests overlap. In the Southern Hemisphere, unique species such as Eucalyptus and Nothofagus are prevalent.


Falling leaves combined with damp conditions and plentiful fungi and bacteria, results in rapid decomposition of leaf litter, animal remains and other forest biomass. So, soil is typically high in nutrients with a high content of organic-rich humus.


Animals in temperate deciduous forests must adapt to the changing seasons – the cold winters and hot summers. Some animals hibernate during the winter to escape the cold. Animals who do not hibernate must find other ways to hide, because when the forest loses its leaves, there is less cover in which to hide from predators.

Black bears are especially well adapted for the deciduous forest biome. They have thick coats to deal with the winter cold, long claws to help them climb trees (whose hollows provide fine shelter), and they eat almost anything. They also hibernate to avoid the struggle of finding food in the snowy winter. Other forest animals include: red foxes, white-tailed deer, raccoons, opossums, porcupines, squirrels, mice, frogs, lizards, as well as spiders, slugs and many other insects. Birds include: woodpeckers, cardinals, snowy owls, broad-winged hawks and more.

Effects of Climate Change on Temperate Forest Biome

The main effect of climate change on temperate forests is a gradual warming resulting from the migration of tropical-style temperatures away from the equator. This leads to a gradual change in the characteristic habitats of the biome. Species of plants, animals and insects have to compete with newcomers arriving from sub-tropical eco-regions, and such changes often tip certain species into near-extinction. The arrival in North America and Europe of sub-tropical giant hornets from Asia, which poses an existential threat to native bee populations, is a case in point. Any major loss of indigenous pollinators could pose a serious threat to plant reproduction throughout this biome.

Effects of Climate Change on Animals.

5. Temperate Grassland Biome

Flowers of The South African Veldt
South African veldt with expanse of wild grasses and flowers.

Temperate grasslands are large, rolling expanses of grasses, sprinkled with a variety of flowers and herbs. 17


Like temperate forests, these grasslands are found mostly at a latitude of 40-60° north and south of the equator. Grasslands are known by different names in different parts of the World: ‘Prairies’ in Canada and the United states; ‘Pampas’ in Argentina and Uruguay; ‘veldts’ in Southern Africa; ‘puszta’ in Hungary; and ‘steppes’ in Russia, China and Mongolia. It is the most widespread of all biomes, but this is due mainly to human deforestation of wooded areas for grazing and agricultural purposes.

The grassland biome is considered by some scientists to be a transitional biome – a halfway stage between the forest and desert biomes. A grassland can turn into either a desert or a forest if climatic conditions (temperature, level of precipitation) change. Basically, grasslands tend to emerge in places where there is not enough rainfall to support a forest, but not so little that a desert biome forms.

The exact origin and evolution of temperate grasslands is unknown, but fossil remains in Chile and the United States suggests that they first formed around 30 million BC, although it wasn’t until 21 million BC that the early forests of North America’s Great Plains region began to die away due to a drop in global rainfall. 18 Grasses have evolved a more efficient method of photosynthesis that requires less water, and so they could survive in arid areas, while forests could not.


The temperate grassland biome enjoys hot summers and cold winters, with temperatures varying by as much as 40 °C (72 °F) between summer and winter. Mean January temperatures vary from minus 18 °C (0 °F) in northern areas to 10 °C (50 °F) in the south. Mean July temperatures range from 18 °C (64 °F) to 28 °C (82 °F), sometimes exceeding 100°F (37.8°C). Mean annual temperature in the most northerly areas of the Canadian grassland biome is below 0 °C (32 °F).

Rain usually occurs in the late spring and early summer. The yearly average is 555-950mm (20-35 inches), but much of this falls as snow in the winter. There are two real seasons: a growing season (100-175 days) and a dormant season, dominated by frost, when no plants can grow.


Temperate grasslands have some of the richest soils in the world, making them ideal for cultivation and farming. 19 The richness stems from the growth and decomposition of deep, many-branched grass roots that raise the organic content of the soil.

The prairies are the granaries of North America, while the Ukrainian steppes were always seen as the bread basket of Russia. The main grassland crops include: Spring Wheat, Corn, Oats, Barley, Rye, Soybeans, Flax, Canola, Yellow and Green Peas, Edible Beans, Mustard and Sunflowers.


Not surprisingly grasses dominate temperate grasslands. The dominant wild grasses include big bluestem, switchgrass, and Indian grass, purple needlegrass, foxtail, ryegrass, and buffalo grass. Many herbivores eat these grasses, but they survive because their growth point is very close to the ground. Also, unlike shrubs and trees, grasses have evolved so that as long as their roots survive, they can grow back after a wildfire very quickly. Wildflowers that grow well in the temperate grassland biome include: asters, blazing stars, clovers, coneflowers, crazy weed, goldenrods, wild indigos and sunflowers.


Grasslands offer little or no shelter from predators. The most numerous species are plant-eating ungulates (mammals with hoofs), whose long legs help them to outrun predators. They also travel in herds for protection. Among the animals that inhabit temperate grasslands in North America are bison, elk, antelope, birds, gophers, bobcats, prairie dogs, coyotes, and gray wolves. Birds include: eagles, fly catchers, Canadian geese, as well as wild turkeys and prairie chickens. On the steppes you can also see falcons as well as antelopes, wild horses, and foxes.

Environmental and Climate Concerns About the Temperate Grasslands Biome

Because temperate grasslands have very rich soil, the majority of grassland in the United States has been converted into fields for crops or grazing land for livestock. Instead of native grasses, grasslands supply corn, wheat, and other grains, as well as grazing for sheep and cattle. Unfortunately, given the pressing need for more food to keep pace with the growing number of people, this native biome is likely to disappear completely.

The big question is, will farmers come up with a sufficiently robust climate change adaptation plan to combat rising temperatures that threaten crop survival. Will they be able to develop heat-resistant varieties of wheat and corn?

6. Savanna Biome

Cheetah in African Savanna
In 1900, more than 100,000 cheetahs roamed the African savanna. Today, less than 12,000 remain. With a top speed of 70 miles per hour, these black-spotted cats hold the record as the fastest land mammal. Photo: © WWF

Savannas are grasslands with a few trees. Like temperate grasslands, they are considered to be a transitional biome – a halfway point between forest and desert. Popularized by TV wildlife documentaries showing lions chasing wildebeest, elephants stripping trees of foliage, or hippos splashing around in muddy pools, savannas are the location for most African safaris, owing to the presence of so many big game animals.


The most famous example of the savanna biome is the Serengeti Plains of Tanzania, covering 30,000 sq km (12,000 sq miles) of land. 20 Nearly half of Africa is covered with savannas. But they are also found in South America, India and even Australia. However, these other regions lack the biological diversity of Africa’s plants and animals.

Savannas are characterized more by their warm climates than by their grasses and scattered trees. They must have a wet season to allow vegetation to grow, as well as a reasonably long dry season to prevent the growth of trees, as trees cannot usually tolerate drought.

There are two fundamental types of savanna: climatic and derived. Climatic savannas are those created by nature and defined strictly by the climate. Derived savannas are artificially created by humans, usually, as a result of forest being converted to grassland for cattle grazing. Sometimes, animals are responsible. Lightly forested areas in Africa have been converted to savanna because elephants have stripped all the bark and vegetation, bulldozed the trees and tramping on saplings.


The Savanna climate is hot with only two seasons: a warm wet season (6-8 months) and a hot dry season (4-6 months). The timing varies from Northern to Southern Hemisphere. In the Serengeti, for example, the dry season runs from June to October, while the wet season runs from November to May, although it is divided into two differing periods. The ‘short rains’ last from November to December, and the ‘long rains’ from March to May.

In fact, the length of the dry season determines the category of savanna. In wet savannas, dry seasons usually last 3-5 months; in dry savannas, 5-7 months, and in ‘thorn bush savannas’ 8 months or longer. During this period no more than 75-100mm (3-4 inches) of rain will fall. Which is why you don’t see many trees.

Mean annual temperatures range from 20 to 30°C (68° to 86°F). Annual rainfall is 250-1200mm (10-50 inches) per year, but nearly all of this falls in the wet season. Tropical grasslands get hot and very humid during the wet season. Every day the warm humid air rises and collides with cooler air above, and turns into rain. In the afternoons, the rains can pour for hours, allowing the grass and other vegetation to grow thick and lush, creating a perfect habitat for herbivores and predators to feed.


Vegetation in the tropical savanna biome is dominated by grasses. Species include: star grass, Rhodes grass, red oats grass, lemon grass, and some shrubs. Most types of grass are coarse and grow only in patches interspersed with areas of bare ground. Only individual trees (baobab tree, acacia tree), or small groves of trees are found, usually near streams and pools. 21

The challenge for any plant in this environment is to survive long periods of drought. To do this, many plants have developed long tap roots that can reach as far as the deep-water table, as well as thick bark to resist annual wildfires, and trunks that are able to store water. Grasses have found ways of discouraging animals from grazing on them; they may be too sharp or bitter tasting for some animals, but okay for others. Different species prefer to eat different parts of the grass. Many grasses grow from the roots up, so that the growth tissue doesn’t get damaged by herbivores.


The savanna biome is home to a wide diversity of animals, although not all species found in Africa are found elsewhere. The best-known animals include: African elephants, lions, leopards, cheetahs, wild dogs, hyenas, warthogs and buffaloes. When it comes to herbivores, who provide most of the prey for predators, they include: zebras, giraffes, wildebeest, gazelles, antelopes, and impala, to name but a few. In all there are more than 40 species of hoofed mammals living in the African savanna.

The intense competition for water during the dry season drives birds and many of the large mammals to migrate in search of water. The great Serengeti wildebeest migration, for example, involves millions of Grant’s gazelle, Thomson’s gazelle, eland, impala and zebras, in a circular migration in search of fresh grazing and better-quality water. The exact timing of the migration depends entirely on the year’s particular pattern of rainfall.

To cope with the searing heat of the dry season, some animals dig burrows in the ground, where they can escape the heat of the day, or provide shelter for their young. Others (hippos, crocodiles) wallow in the mud of the dwindling water holes.

Some animals are able to exploit the heat. There are many species of birds of prey overflying the savanna, including eagles, hawks, buzzards and vultures. Because hot air rises, the birds can soar on the air using almost no energy. They can spend all day soaring over large areas of land, using their keen eyesight to spot prey.

Some creatures burrow but fail to escape the attentions of specialist predators. Termite mounds, for instance, are a common sight on the South African veldt and elsewhere. In fact, there are more than 1,000 different kinds of termites living in African savannas – more than anywhere else in the world. These termite colonies support numerous predators, such as the aardvark and aardwolf in Africa, and giant anteater in South America.

Ultimately, the ecosystem of the savanna is based on a balanced system of interdependence. Herbivores are the major food source for most predators, but they also depend upon predators to eliminate aging or diseased animals, to maintain the health of the herds.

To reduce unnecessary competition for scarce food resources, each of the many species of herbivores has its own preference for grass, allowing up to 16 different species of grazers to coexist in the same area at one time. In addition, most of the herds keep moving.

By contrast. in several areas of the African savanna, farmers have begun using it to graze their cattle and goats. They don’t move their herds around, so the grasses are soon completely eaten, turning the now grassless plain into a desert. Considerable areas of savanna are lost to the Sahara Desert every year due to overgrazing.

Environmental and Climate Concerns About the Savanna Biome

Humans are the biggest danger to the tropical grassland biome and its biodiversity of plants and animals. Poaching, expansion of farming and commercial development, do untold damage to animals and birds. The impact of climate change is also being felt, as rising temperatures evaporate water supplies and damage animal habitats. Growing populations are likely to increase the pressure on food and land resources, damaging the savanna biome in the process.

7. Tropical Rainforest Biome

Boa constrictor snake, native to South America
Boa constrictor snake, native to the Amazonian rainforest biome, South America.

Tropical rainforests are one of Earth’s most important and most fragile ecological environments. In recent decades, almost half of the rainforest biome has disappeared due to deforestation and commercial development.


Tropical rainforests cover roughly 6 percent of the Earth’s land surface and are generally located around the world, between 30°N and 30°S. They occur in Central and South America; in Western Africa, and the Congo basin; and along the west coast of India, Southeast Asia, New Guinea, and Northern Queensland, Australia. The largest and most famous example is the Amazon Rainforest, most of which is in Brazil. The next largest is the Congo Rainforest in Equatorial West Africa.

The rainforest biome is critically important to Earth’s climate because it helps to maintain global weather patterns and rainfall, while acting as a home to the world’s largest collection of animal and plant species. 22


The climate of the tropical rainforest biome is hot and wet all year round. The average temperature hovers around 21-30°C (70-85°F), and doesn’t vary much even between night and day. The humidity remains between 77 percent and 88 percent all year-round. Mean average rainfall is 2000-10000mm (80-400 inches) annually.


Most trees in tropical rainforests have thin, smooth bark, which makes it difficult for other plants, such as epiphytes, to grow on their surface. Trees often have large branching ridges near their base, to help offset their shallow roots. Many plants have adapted leaf shapes that allow water to drain away quickly to minimize surface moisture that might facilitate the growth of bacteria and fungi.


Tropical rainforests are commonly divided into four layers. The top layer of the rainforest is called the emergent layer. This is headed by giant trees that are much taller than their shorter companions below.

The next layer down is the canopy. It consists of trees standing 18 to 45 meters (60 to 150 feet) tall. Their branches form a canopy, not unlike a big golf umbrella, that shades the forest floor. Thick, woody vines (such as lianas) also form part of the canopy. They climb the trunks of trees in the canopy in order to reach for sunlight.

The next layer down, the understory, is a dark, cool area which is below and shaded by the canopy, but above the ground. Beneath the understory is the forest floor, the bottom layer of the rainforest. This is where fallen branches, plants and forest litter lie, rapidly decomposing thanks to the millions of bacteria, fungi, insects and other decomposers that work hard to recycle nutrients contained in the rotting vegetation and animal remains.


Tropical rainforests provide shelter for half the plant and animal species on Earth. Scientists believe this diversity of animals stems from the fact that rainforests are one of the oldest ecosystems on earth. Some Southeast Asian forests are at least 100 million years old.

Animals able to survive the tropical rainforest have invariably adapted themselves to live in this unique environment. For example, many mammals, birds, reptiles and amphibians have developed the ability to live in trees. Most animals in the tropical rainforest biome, live in the canopy. It’s safer, and food is abundant.

Birds play an important role in rainforests because they eat seeds and fruit. Their seed-rich droppings grow into new plants and help rainforests to propagate. Monkeys also eat fruit, spitting out seeds onto the forest floor with similar effect, as they move from tree to tree. In turn, tropical rainforests are important to birds because they provide winter grounds as migratory destination.

The tropical rainforest biome provides oxygen, absorbs more carbon dioxide than it releases, creates its own rainfall, plays a vital role in the water cycle and the carbon cycle, and is home to an astonishing diversity of trees, plants, animals, birds and insects.

Rainforests also provide people with food and a host of spices, including: allspice, bananas, black pepper, cacao, cassava, ginger, nutmeg, sugar cane, vanilla, and many more. A number of large pharmaceutical companies maintain research offices in the Amazon, to bio prospect for new pharmacological and medical materials. A huge proportion of drugs originate from inside the rainforest biome.

Effects of Humans and Climate Change on the Tropical Rainforest Biome

Unfortunately, many unemployed people are moving into the rainforest from crowded cities in order to become small farmers. They use slash-and-burn methods to clear the land either for their own smallholdings or for larger ranchers.

Add to this, an increase in logging operations for fuelwood, charcoal, building materials and other uses, as well as the mining for gold, bauxite, and other minerals, and you can see the stress that is being placed on rainforests around the world.

Most of the African rainforest has already been cleared. (According to the U.N. FAO, during the period 2000-2005, Nigeria lost more than half of its primary forest. During 2014-2018, the rate of deforestation in the Democratic Republic of Congo doubled.) Deforestation in the Amazon Rainforest is also significantly up, while surviving tracts in the Philippines and Sumatra are equally threatened. 23

Climate change is also having an effect. As temperatures rise, there is a risk that rainforests – notably those in the Amazon Basin – will dry out, leading to a savannization of the entire Amazonian biome. This may lead to a significant change in the climate of Central America and the Southern United States. 24

8. Desert Biome

Oasis in Libyan Desert
Oasis in the Libyan part of the Sahara Desert. Photo: © Sfivat/Wiki Commons

Desert biomes are characterized by extremely low rainfall. In fact, deserts are the driest places on Earth, making them inhospitable to most forms of life. 25 Most experience periods of intense drought during which rain may not fall for several years. Not surprisingly, desert biodiversity of plants and animals is very low.


Generally, deserts are located between 15° and 30° north and south of the equator (the mid-latitudes), typically in a belt of high pressure (sinking air) and very low rainfall. The best-known deserts include: the Sahara Desert (North Africa), the Arabian Desert (Arabian Peninsula), the Western Deserts of Australia, the Kalahari Desert (Southern Africa), the Mojave Desert (USA) and the Atacama Desert (Chile & Peru).


The desert biome climate is extremely hot and dry, typically receiving less than 250mm (10 inches) of rainfall per year. In some deserts, it might rain only once every two or three years. And when it does, the rain often falls in short violent bursts. Occasionally, the rain evaporates before even hitting the ground, while the hard ground often means that the soil is unable to absorb more than a tiny amount, leaving most to be lost in run-off. It is extremely hot during the day, with temperatures averaging 38°C (100°F). Cloudless skies during the early hours of darkness ensure that most of the daytime heat escapes, causing night-time temperatures to plunge as low as minus 4°C (24°F). The temperature also varies according to the location of the desert.

By contrast, coastal deserts, like the Atacama Desert on the western coast of South America, are found in moderately cool to warm areas. They usually experience cool winters (average 5°C/41°F) followed by long, warm summers (12-24°C/55-75°F). Rainfall remains extremely low, however, averaging 80-130mm (3-5 inches) annually. Although it has a relatively mild climate, the Atacama is the Earth’s driest desert, with 1mm or of rain about every 5-20 years.


To cope with the arid conditions, desert plants need to excel at storing and finding water. Some plants, like cacti, have shallow roots that are widely spread allowing any rain to be absorbed immediately. They store water in their stems and use it very slowly, while other plants conserve water by having large root systems to gather water from the deep-water table. Some plant species live only for a few weeks, during periods of rain. 26 Other common plants that inhabit the desert include sagebrush, creosote bush, and ocotillo.

Coastal deserts house a variety of plants, such as black sage, chrysothamnus, rice grass and salt bush. These plants grow complex root systems that come up to the surface to absorb any possible rainfall, and also stretch deep down to absorb any water held in the ground. These plants also develop very thick leaves that can absorb water whenever it becomes available.


The desert biome is home to a mixed bag of animals. The most famous animal in the desert is the camel. Camels are extremely well adapted. They have two rows of eyelashes to protect their eyes from the dust; they carry fat in their hump so they can go for days without food and they can close their nostrils to stop them inhaling sand.

Kangaroo rats are another success story. They live in complex burrow systems, sometimes in colonies of several hundred dens. To ensure a cool temperature in their burrows, they plug the entrances with soil during the day and venture out only at night. kangaroo rats are extremely fast and agile, and can often leap up to 2.75m (9 feet) at speeds up to 2.75m (10 ft) per second. Kangaroo rats are mostly seed eaters and often store the seeds of mesquite, creosote bush, purslane and ocotillo in seed caches for future use.

Other desert animals that avoid the sun are the nocturnal fennec fox, who comes out to hunt only after sunset, and the desert tortoise that also spends much of its time underground.

The Armadillo Lizard of the deserts of Southern Africa, relies on camouflage, an ability to freeze, and a thick skin to survive the attentions of predators. It lives in the cracks and crevices of large rocks.

Funny Photo of Meerkats, Kalahari Desert
Meerkats are found in the western and southern parts of Africa, in the Kalahari Desert. A highly social animal they usually stick together in groups of 10 to 30 individuals. Photo: © Ecophoto|

Like the kangaroo rat, the meerkats of the Kalahari Desert in Southern Africa live in complex underground tunnel systems that they have either dug or inherited from a previous occupant. While a group of meerkats is hunting for food, one or more will act as lookout on its hind legs to watch for predators.

The Sidewinder Rattlesnake of the Southwestern United States uses venom to kill its prey. During the day it hides in the sand or in animal burrows, before emerging at night to hunt.

Effects of Humans and Climate Change on the Desert Biome

Deserts have probably the least to fear from climate change as they deal with hot and arid conditions every day. It’s actually the semi-arid eco-zones adjacent to it, that are suffering. They are suffering from desertification, caused mostly by deforestation and the degradation of the soil through over intensive grazing, agriculture and loss of vegetation, all of which encourage soil erosion by wind and water.

In China, inappropriate land use in the form of expanding urbanization has left much of the land exposed to wind erosion and dust storms from the surrounding desert, necessitating the construction of a so-called “great green wall” to hold back the advancing desert.

Global warming is only likely to exacerbate these environmental problems by exaggerating extreme weather events and climate oscillations, leading to more severe drought, heatwaves, and flooding. Ironically, far from shrinking the desert biome, climate change is likely only to enlarge it.

9. Freshwater Biome

Beautiful Lakes in Switzerland, Seealpsee
Seealpsee fresh water lake in the Alpstein mountain range, Switzerland. Photo: © LostinSwitzerland

The freshwater biome is one of Earth’s aquatic ecosystems and an important element in the ecology of the hydrosphere. It encompasses three basic environments: (a) lakes and ponds, (b) streams and rivers, and (c) wetlands. 27 These habitats are classified as either “lentic” (still water) – which includes ponds, lakes, and wetlands; or “lotic” (flowing water) – which includes streams and rivers; or “groundwaters” which flow in aquifers and rocks. Note: the terms freshwater and fresh water are interchangeable. 28

What is Freshwater?

Freshwater is water with less than 500 parts per million (ppm) of dissolved salts. (Source: Groundwater Foundation.) It is not the same as drinking water (potable water). Much of Earth’s freshwater is not suitable for drinking without some form of treatment.

How Much of Earth’s Water is Freshwater?

Almost all the water on Earth is saline. Roughly 97 percent comes from oceans and seas. Only about 2.75 percent is fresh water, most of which is locked up in glaciers and ice sheets. Only about 0.01 percent of Earth’s water is found in lakes, swamps and rivers.

What is Brackish Water?

“Brackish water” is a general term used to describe water that is more saline than freshwater but less saline than seawater. It commonly occurs in estuaries and coastal wetlands where seawater and freshwater mix together.

Salinity Table

Water TypeSalinity Level
Fresh waterLess than 0.05%
Brackish water0.05–3%
Saline water3–5%
Brine5%-26% max

Where Does Freshwater Come From?

Almost all fresh water comes from the atmosphere in the form of mist, rain and snow. It comes originally from the ocean (or lakes, reservoirs, rivers), from where it evaporates into the air. Here the vapor condenses into water droplets, forms clouds and eventually precipitates (falls), usually as rain or snow. During its journey through the water cycle, this freshwater absorbs chemicals and other materials from the atmosphere, and from the sea and land mass over which it travels.

Lakes and Ponds

These lentic ecosystems vary in size from a few square meters to thousands of square kilometers. Lakes may endure for centuries but many ponds are seasonal, lasting as long as the rainy season. Species biodiversity of this freshwater biome is usually limited owing to its isolated and fragmented geography.

Lakes and ponds are commonly divided into three different “zones” according to their depth and distance from the shore.

The zone nearest the shore is known as the littoral zone. This is the shallowest zone, and absorbs most of the sunlight, making it the warmest and lightest part of the water. The littoral zone has a fairly diverse ecological community, which includes several species of micro-algae (plankton, such as diatoms), floating and rooted aquatic plants such as water lilies, and duckweed, snails, crustaceans, fishes, and amphibians. Eggs and larvae of insects, like midges and dragonflies, are also found here. The creatures and organisms living in the littoral zone provide food for other creatures like turtles, snakes, bigger fish, ducks and certain birds of prey.

The upper level of the lake or pond away from the shore is the limnetic zone. Being near the surface, this layer is also well-lit and (as a result) is dominated by both phytoplankton and the zooplankton who feed on them. Plankton are micro size drifting organisms that play a critical role in the Earth’s food chain. See also: Marine Microbes Drive the Aquatic Food Web.

Phytoplankton are the world’s most important primary producers (photosynthesizers), and supply most of the world’s oxygen. Without aquatic plankton, there would be few living things left in the world. The limnetic zone also sustains a variety of freshwater fish.

The lower levels of the lake – the deepest water – is known as the profundal zone. This zone is colder, denser and darker than the other two, since little if any sunlight can reach it. Organisms in the profundal zone are heterotrophs, meaning that – unlike plankton – they cannot photosynthesize and must obtain their food in the normal way – that is, by eating something. Fortunately, plants and organisms living in the littoral or limnetic zones fall into the profundal zone when they die, providing plenty of food for the latter’s inhabitants.

Temperature within ponds and lakes changes with the seasons. In summer, temperatures can vary from 4°C at the bottom to 22° C at the top. In winter, if the temperature at the bottom is 4°C, the water at the top could be 0°C (frozen). In spring and autumn, the top and bottom layers tend to mix, because of winds, which produces a uniform lake or pond temperature of about 4° C. This mixing of water also helps to keep the lake healthy by circulating oxygen from top to bottom.

Streams and Rivers

This part of the freshwater biome is a lotic (flowing) system in which water is constantly moving in one direction. These habitats typically stretch from springs or headwaters (or snow melt), located in hilly or mountainous terrain, all the way to the sea. As the topography and vegetation changes along the route, so does the character of the biome. For example, the temperature is typically cooler in the mountains than it is at the mouth of the river. And because there is less sediment higher up, the water is also clearer, with a higher oxygen content, which means fish like trout are more plentiful. As the altitude drops and the river widens, the number of fish species increases, as does the number and diversity of aquatic plants and algae. Near the mouth of the river, the water typically gets murkier from all the soil and sediments carried downstream due to erosion. With less light, there are fewer plants, and less oxygen, so the fish that appear in this section of the river tend to be species like catfish and carp, who have adapted to a low oxygen environment.

Over time, rivers flowing over flat land can create separate ponds and wetlands. For example, as the river becomes more sluggish with sediment, it tends to meander. As a result, sediments carried along tend to deposit on the inside of the bend, creating larger and more exaggerated bends. Ultimately, the river refuses to bend anymore and takes the shortest course, leaving the old bend behind. These U-shaped bends that become isolated from the main river are known as oxbow lakes. They continue to develop biologically but as a lentic rather than a lotic ecosystem.

Freshwater Wetlands

Freshwater wetlands are areas of standing water (permanently or seasonally flooded) that support aquatic plants. 29 Bogs, marshes, swamps, fens and floodplains are all considered wetlands. What defines them is the aquatic plants (hydrophytes) they support, that have adapted to the area’s hydric soils, and the fact that oxygen-free processes dominate. Such plants include: cattails, pond lilies, sedges, tamarack, and black spruce. Wetlands have one of the richest varieties of animal species of all ecosystems, including reptiles, amphibians (frogs, toads and salamanders), leeches and birds (notably ducks and waders). Insects are also widespread. They pollinate plants and provide food for amphibians and birds.


Since wetlands are defined by their water, they are found all over the world in different climates. As a result, temperatures vary according to their geographical location. Many are in found temperate zones, midway between the poles and the equator. Here, cold winters and warm summers are the norm, but temperatures are not extreme. In the tropics, wetlands are much warmer for a larger portion of the year. In the Pantanal, for example, temperatures during the year range from 20-33°C (68-91°F). In Western Siberia, average January temperatures range from minus 15 °C (5 °F) in the southwest to minus 30 °C (minus 22 °F) in the northwest. Average July temperatures, range from 20 °C (68 °F) in the south to 20 °C (68 °F) in the north.

The amount of rainfall a wetland receives varies widely for the same reason. Wetlands in Ireland and the UK typically receive about 1,500 mm (59 inches) of rain, annually. In the Pantanal, mean annual rainfall is 1100mm (43 inches), while in Southeast Asia, wetlands can receive up to 10,000mm (390 in).

Wetlands have a number of important environmental and climatic functions. They slow down rainwater runoff and spring snow melt; they store water and help prevent floods; they retain nutrients in the soil and help purify water – a number of floating plant species, for example, are able to absorb and filter heavy metals; and they sustain a hugely diverse plant and animal kingdom. On the coast, they stabilize shorelines, although coastal wetlands – famous for their reservoirs of “blue carbon” – are not classified as freshwater ecosystems as their waters are too saline.

The most extensive freshwater wetlands are the Pantanal in South America (220,000 km), the Amazon River basin, Esteros del Ibera (Argentina) (12,000 sq km), the Florida Everglades (20,000 sq km), the Okefenokee Swamp in Georgia (1,700 sq km), Ngiri-Tumba-Maindombe (Democratic Republic of the Congo) (66,000 sq km), Sudd (South Sudan) (57,000 sq km), Plaines d’inondation des Bahr Aouk et Salamat (Chad) (49,000 sq km), Okavango Delta (Botswana) (55,000 sq km), Gueltas et Oasis de l’Air (Niger) (49,000 sq km), and the West Siberian Plain (2.6 million sq km).

For a short review of our climate crisis, see: Climate Change Essay in 1000 words.

Effects of Humans and Climate Change on the Freshwater Biome

Global warming affects all freshwater habitats. As snow becomes scarcer in Alpine areas, river flow is reduced, and lake water levels fall. Wetland habitats also start to dry out. Larger eco-regions like the Amazon Rainforest are shrinking and may tip over into a form of savanna, which could easily have a catastrophic effect on surrounding wetlands, including the Pantanal.

It’s worth noting that all wetlands – from temperate freshwater wetlands to boreal peatlands – store carbon dioxide from the atmosphere, in their vegetation and soils. This atmospheric carbon dioxide, which is the main driver of climate change, comes from the burning of fossil fuels around the world. If temperatures continue to rise, or if humans continue to drain wetlands, then more and more of this stored carbon dioxide will be released into the atmosphere, with serious consequences for us all.

The Ocean Biome

Lack of space precludes a review of the numerous ocean biomes, but here is a short selection of articles that you might be interested in.

Marine Microbes Drive the Aquatic Food Web
What are Mangroves? Why are they Important?
Coral Reefs are Dying From Climate Change


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  21. See also: “Nature’s green revolution: the remarkable evolutionary rise of C4 plants.” Osborne, Colin P.; Beerling, David J. (2006). Philosophical Transactions of the Royal Society B. 361 (1465): 173–194. []
  22. Land-use and climate change risks in the Amazon and the need of a novel sustainable development paradigm“. A. Nobre et al; September 27, 2016. Proceedings of the National Academy of Sciences of the United States of America. 113 (39): 10759–10768. []
  23. The future of Southeast Asia’s forests. ” Estoque, R.C., Ooba, M., Avitabile, V. et al. Nat Commun 10, 1829 (2019). []
  24. Amazon Tipping Point.” Thomas E. Lovejoy and Carlos Nobre. Science Advances 21 Feb 2018: Vol. 4, no. 2 []
  25. “In the Deserts of this Earth.” George, Uwe (1978). Hamish Hamilton. ISBN 978-0-241-89777-5 []
  26. How Plants Cope with the Desert Climate.” []
  27. “Limnology: lake and river ecosystems” (3rd ed.) Wetzel, Robert (2001). San Diego: Academic Press. ISBN 978-0127447605. []
  28. Major Freshwater Biomes.[]
  29. “Wetland Ecology : principles and conservation (2nd ed.)” Keddy, P.A. (2010) New York: Cambridge University Press. ISBN 978-0521519403. []
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