Terrestrial Biomes

Lesson Content

Inquire: Terrestrial Biomes

Overview

Earth has terrestrial and aquatic biomes. Aquatic biomes include both freshwater and marine environments. There are eight major terrestrial biomes: tropical rainforests, savannas, subtropical deserts, chaparral, temperate grasslands, temperate forests, boreal forests, and Arctic tundra. The same biome can occur in different geographic locations with similar climates. Temperature and precipitation, and variations in both, are key abiotic factors that shape the composition of animal and plant communities in terrestrial biomes. Some biomes, such as temperate grasslands and temperate forests, have distinct seasons with cold and hot weather alternating throughout the year. In warm, moist biomes, such as the tropical rainforest, net primary productivity is high as warm temperatures, abundant water, and a year-round growing season fuel plant growth. Other biomes, such as deserts and tundra, have low primary productivity due to extreme temperatures and a shortage of water.

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Big Question

What are the distinguishing characteristics of each of the eight major terrestrial biomes?

Read: Terrestrial Biomes

Overview

Earth’s biomes can be terrestrial or aquatic; terrestrial biomes are land based. The eight major terrestrial biomes on Earth are each distinguished by characteristic temperatures and precipitation levels. Annual totals and fluctuations of precipitation affect the kinds of vegetation and animal life that can exist in broad geographical regions. Temperature variation on a daily and seasonal basis is also important for predicting the geographic distribution of a biome. Since a biome is defined by climate, the same biome can occur in geographically distinct areas with similar climates. There are large areas of land in Antarctica, Greenland, and in mountain ranges that are covered by permanent glaciers and support very little life. Strictly speaking, these are not considered biomes and in addition to extremes of cold, they are also often deserts with very low precipitation.

Tropical Forest

Tropical rainforests are also referred to as tropical wet forests. This biome is found in equatorial regions. Tropical rainforests are the most diverse terrestrial biome. This biodiversity remains largely unexplored and is under extraordinary threat primarily through logging and deforestation for agriculture. Tropical rainforests have also been described as “nature’s pharmacy,” because of the potential for new drugs that is largely hidden in the chemicals produced by the huge diversity of plants, animals, and other organisms. The vegetation is characterized by plants with spreading roots and broad leaves that fall off throughout the year, unlike the trees of deciduous forests that lose their leaves in one season. These forests are “evergreen,” or year-round.

The temperature and sunlight profiles of tropical rainforests are stable. Average temperatures range from 20oC to 34oC (68oF to 93oF). Month-to-month temperatures are relatively constant in tropical rainforests. This lack of temperature seasonality leads to year-round plant growth. A constant daily amount of sunlight (11–12 hours per day) provides more solar radiation, thereby a longer period of time for plant growth.

The annual rainfall in tropical rainforests ranges from 250 cm to more than 450 cm (8.2–14.8 ft) with considerable seasonal variation. Tropical rainforests have wet months in which there can be more than 30 cm (11–12 in) of precipitation, as well as dry months in which there are fewer than 10 cm (3.5 in) of rainfall.

DecorativeTropical rainforests have high net primary productivity because the annual temperatures and precipitation values support rapid plant growth. The high rainfall quickly leaches nutrients from the soils of these forests, which are typically low in nutrients. Tropical rainforests are characterized by vertical layering of vegetation and the formation of distinct habitats for animals within each layer. On the forest floor is a sparse layer of plants and decaying plant matter. Above that is an understory of short, shrubby foliage. A layer of trees rises above this understory and is topped by a closed upper canopy — the uppermost overhead layer of branches and leaves. Some additional trees emerge through this closed upper canopy. These layers provide diverse and complex habitats for the variety of plants, animals, and other organisms within the tropical wet forests. Many species of animals use the variety of plants and the complex structure of the tropical wet forests for food and shelter. Some organisms live several meters above ground rarely ever descending to the forest floor.

Boreal Forests

The boreal forest, also known as taiga or coniferous forest, is found across most of Canada, Alaska, Russia, and northern Europe. Boreal forests are also found above a certain elevation in mountain ranges throughout the Northern Hemisphere. This biome has cold, dry winters and short, cool, wet summers. The annual precipitation is from 40 cm to 100 cm (15.7–39 in) and usually takes the form of snow; little evaporation occurs because of the cold temperatures.

The long and cold winters in the boreal forest have led to the predominance of cold-tolerant cone-bearing plants. These are evergreen coniferous trees like pines, spruce, and fir, which retain their needle-shaped leaves year-round. Evergreen trees can photosynthesize earlier in the spring than deciduous trees because less energy from the sun is required to warm a needle-like leaf than a broadleaf. Evergreen trees grow faster than deciduous trees in the boreal forest. In addition, soils in boreal forest regions tend to be acidic with little available nitrogen. Leaves are a nitrogen-rich structure and deciduous trees must produce a new set of these nitrogen-rich structures each year. Therefore, coniferous trees that retain nitrogen-rich needles in a nitrogen limiting environment may have had a competitive advantage over the broad-leafed deciduous trees.

DecorativeThe aboveground biomass of boreal forests is high because these slow-growing tree species are long-lived and accumulate standing biomass over time. Species diversity is less than that seen in temperate forests and tropical rainforests. Boreal forests lack the layered forest structure seen in tropical rainforests or, to a lesser degree, in temperate forests. The structure of a boreal forest is often only a tree layer and a ground layer. When conifer needles are dropped, they decompose more slowly than broad leaves; therefore, fewer nutrients are returned to the soil to fuel plant growth.

Temperate Forests

Temperate forests are the most common biome in eastern North America, Western Europe, Eastern Asia, Chile, and New Zealand. Temperatures range between –30oC and 30oC (–22oF to 86oF) and drop to below freezing on an annual basis. These temperatures mean that temperate forests have defined growing seasons during the spring, summer, and early fall. Precipitation is relatively constant throughout the year and ranges between 75 cm and 150 cm (29.5–59 in).

Deciduous trees are the dominant plant in this biome with fewer evergreen conifers. Deciduous trees lose their leaves each fall and remain leafless in the winter. Little photosynthesis occurs during the dormant winter period. Each spring, new leaves appear as temperature increases. Because of the dormant period, the net primary productivity of temperate forests is less than that of tropical rainforests. In addition, temperate forests show far less diversity of tree species than tropical rainforest biomes.

DecorativeThe trees of the temperate forests leaf out and shade much of the ground; however, more sunlight reaches the ground in this biome than in tropical rainforests because trees in temperate forests do not grow as tall as the trees in tropical rainforests. The soils of the temperate forests are rich in inorganic and organic nutrients compared to tropical rainforests. This is because of the thick layer of leaf litter on forest floors and reduced leaching of nutrients by rainfall. As this leaf litter decays, nutrients are returned to the soil. The leaf litter also protects soil from erosion, insulates the ground, and provides habitats for invertebrates and their predators.

Reflect: Which Biome Would You Recreate?

Poll

There are eight major terrestrial biomes. The same biome can occur in different geographic locations with similar climates.

The same biome can occur in different geographic locations with similar climates. Which biome would you try to recreate on another planet, if you could?

Expand: Other Terrestrial Biomes

Savannas

DecorativeSavannas are grasslands with scattered trees, and they are found in Africa, South America, and northern Australia. Savannas are hot, tropical areas with temperatures averaging from 24oC –29oC (75oF –84oF) and an annual rainfall of 51–127 cm (20–50 in). Savannas have an extensive dry season and consequent fires. Grasses and herbaceous flowering plants dominate the savanna with relatively few trees. Since fire is an important source of disturbance in this biome, plants have evolved well-developed root systems that allow them to quickly re-sprout after a fire.

Arctic Tundra

The Arctic tundra is located throughout the Arctic regions of the Northern Hemisphere. Tundra also exists at elevations above the tree line on mountains. The average winter temperature is –34°C (–29.2°F) and the average summer temperature is 3°C–12°C (37°F –52°F). Plants in the Arctic tundra have a short growing season of approximately 50–60 days. During this time, there are almost 24 hours of daylight and plant growth is rapid. The annual precipitation of the Arctic tundra is low (15–25 cm or 6–10 in) with little annual variation in precipitation. Little evaporation occurs because of the cold temperatures.

Plants in the Arctic tundra are generally low to the ground and include low shrubs, grasses, lichens, and small flowering plants. There is little species diversity, low net primary productivity, and low aboveground biomass. The soils of the Arctic tundra may remain in a perennially frozen state referred to as permafrost. The permafrost makes it impossible for roots to penetrate far into the soil and slows the decay of organic matter, which inhibits the release of nutrients from organic matter. The melting of the permafrost in the brief summer provides water for a burst of productivity while temperatures and long days permit it. During the growing season, the ground of the Arctic tundra can be completely covered with plants or lichens.

Chaparral

DecorativeThe chaparral is also called scrub forest and is found in California, along the Mediterranean Sea, and along the southern coast of Australia. The annual rainfall in this biome ranges from 65 cm to 75 cm (25.6–29.5 in) and the majority of the rain falls in the winter. Summers are very dry and many chaparral plants are dormant during the summertime. The chaparral vegetation is dominated by shrubs and is adapted to periodic fires, with some plants producing seeds that germinate only after a hot fire. The ashes left behind after a fire are rich in nutrients like nitrogen that fertilize the soil and promote plant regrowth. Fire is a natural part of the chaparral biome’s maintenance, and frequently threatens human habitation in this biome in the U.S..

Temperate Grasslands

Temperate grasslands are found throughout central North America, where they are also known as prairies, and in Eurasia, where they are known as steppes. Temperate grasslands have pronounced annual fluctuations in temperature with hot summers and cold winters. The annual temperature variation produces specific growing seasons for plants. Plant growth is possible when temperatures are warm enough to sustain plant growth, which occurs in the spring, summer, and fall.

Annual precipitation ranges from 25.4 cm to 88.9 cm (10–35 in). Temperate grasslands have few trees except for those found growing along rivers or streams. The dominant vegetation tends to consist of grasses. The treeless condition is maintained by low precipitation, frequent fires, and grazing. The vegetation is very dense and the soils are fertile because the subsurface of the soil is packed with the roots and rhizomes (underground stems) of these grasses. The roots and rhizomes act to anchor plants into the ground and replenish the organic material (humus) in the soil when they die and decay.

DecorativeFires, which are a natural disturbance in temperate grasslands, can be ignited by lightning strikes. It also appears that the lightning-caused fire regime in North American grasslands was made worse by intentional burning by humans. When fire is suppressed in temperate grasslands, the vegetation eventually converts to scrub and dense forests. Often, the restoration or management of temperate grasslands requires the use of controlled burns to suppress the growth of trees and maintain the grasses.

Check Your Knowledge

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Lesson Resources

Lesson Toolbox

Additional Resources and Readings

NASA Earth Observatory

An interactive graphic allowing you to learn more about each biome

MooMoo Math and Science

A video covering the tropical rainforest biome

Planet Earth

A Planet Earth video about the rainforest

National Geographic

A video on America’s northernmost National Park, Gates of the Arctic

Lesson Glossary

Terms

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  • Arctic tundra
    a biome characterized by low average temperatures, brief growing seasons, the presence of permafrost, and limited precipitation largely in the form of snow in which the dominant vegetation are low shrubs, lichens, mosses, and small herbaceous plants
  • boreal forest
    a biome found in temperate and subarctic regions characterized by short growing seasons and dominated structurally by coniferous trees
  • canopy
    the branches and foliage of trees that form a layer of overhead coverage in a forest
  • chaparral
    a biome found in temperate coastal regions characterized by low trees and dry-adapted shrubs and forbs
  • permafrost
    a perennially frozen portion of the Arctic tundra soil
  • savannas
    a biome located in the tropics with an extended dry season and characterized by a grassland with sparsely distributed trees
  • subtropical deserts
    a biome found in the subtropics with hot daily temperatures, very low and unpredictable precipitation, and characterized by a limited dry-adapted vegetation
  • temperate forests
    a biome found in temperate regions with moderate rainfall and dominated structurally by deciduous trees
  • temperate grasslands
    a biome dominated by grasses and herbaceous plants due to low precipitation, periodic fires, and grazing
  • tropical rainforests
    a biome found near the equator characterized by stable temperatures with abundant and seasonal rainfall in which trees form the structurally important vegetation

License and Citations

Content License

Lesson Content:

Authored and curated by Jill Carson for The TEL Library. CC BY NC SA 4.0

Adapted Content:

Title: Biology – 20.3 Terrestrial Biomes -Tropical Forest; Savannas; Deserts: Rice University, OpenStax CNX. License: CC BY 4.0

Media Sources

 LinkAuthorPublisherLicense
DecorativeCerrado DeforestationRosarioXavierPixabayCC 0
DecorativeMissouri CoteauSarah GreenWikimedia CommonsCC BY 2.0
DecorativeArctic TundraU.S. Fish and Wildlife Service HeadquartersWikimedia CommonsCC BY 2.0
DecorativeTypical Bandundu savanna villageNick HobgoodWikimedia CommonsCC BY 2.0
DecorativeTemperate mixed forest near Harbin, ChinaIvanWalsh.comWikimedia CommonsCC BY 2.0
DecorativeBoreal pine forest 6 years after fireHannuWikimedia CommonsPublic Domain
DecorativeWaterfall Jungle CliffFree-PhotosPixabayCC 0