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28.3: Terrestrial Biomes - Biology

28.3: Terrestrial Biomes - Biology


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Earth’s biomes can be either terrestrial or aquatic. Terrestrial biomes are based on land, while aquatic biomes include both ocean and freshwater biomes. The eight major terrestrial biomes on Earth are each distinguished by characteristic temperatures and amount of precipitation. 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 (Figure 20.3.1). There are also large areas on 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 (Figure 20.3.1). Tropical rainforests are the most diverse terrestrial biome. This biodiversity is still largely unknown to science 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,” year-round.

The temperature and sunlight profiles of tropical rainforests are stable in comparison to that of other terrestrial biomes, with average temperatures ranging from 20oC to 34oC (68oF to 93oF). Month-to-month temperatures are relatively constant in tropical rainforests, in contrast to forests further from the equator. This lack of temperature seasonality leads to year-round plant growth, rather than the seasonal growth seen in other biomes. In contrast to other ecosystems, a more 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. However, the driest month of a tropical rainforest can still exceed the annual rainfall of some other biomes, such as deserts.

Tropical rainforests have high net primary productivity because the annual temperatures and precipitation values support rapid plant growth (Figure 20.3.2). However, 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.

Rainforests are not the only forest biome in the tropics; there are also tropical dry forests, which are characterized by a dry season of varying lengths. These forests commonly experience leaf loss during the dry season to one degree or another. The loss of leaves from taller trees during the dry season opens up the canopy and allows sunlight to the forest floor that allows the growth of thick ground-level brush, which is absent in tropical rainforests. Extensive tropical dry forests occur in Africa (including Madagascar), India, southern Mexico, and South America.

Savannas

Savannas are grasslands with scattered trees, and they are found in Africa, South America, and northern Australia (Figure 20.3.1). 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. As a result, scattered in the grasses and forbs (herbaceous flowering plants) that dominate the savanna, there are relatively few trees (Figure 20.3.3). 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.

Deserts

Subtropical deserts exist between 15o and 30o north and south latitude and are centered on the Tropic of Cancer and the Tropic of Capricorn (Figure 20.3.1). Deserts are frequently located on the downwind or lee side of mountain ranges, which create a rain shadow after prevailing winds drop their water content on the mountains. This is typical of the North American deserts, such as the Mohave and Sonoran deserts. Deserts in other regions, such as the Sahara Desert in northern Africa or the Namib Desert in southwestern Africa are dry because of the high-pressure, dry air descending at those latitudes. Subtropical deserts are very dry; evaporation typically exceeds precipitation. Subtropical hot deserts can have daytime soil surface temperatures above 60oC (140oF) and nighttime temperatures approaching 0oC (32oF). The temperature drops so far because there is little water vapor in the air to prevent radiative cooling of the land surface. Subtropical deserts are characterized by low annual precipitation of fewer than 30 cm (12 in) with little monthly variation and lack of predictability in rainfall. Some years may receive tiny amounts of rainfall, while others receive more. In some cases, the annual rainfall can be as low as 2 cm (0.8 in) in subtropical deserts located in central Australia (“the Outback”) and northern Africa.

The low species diversity of this biome is closely related to its low and unpredictable precipitation. Despite the relatively low diversity, desert species exhibit fascinating adaptations to the harshness of their environment. Very dry deserts lack perennial vegetation that lives from one year to the next; instead, many plants are annuals that grow quickly and reproduce when rainfall does occur, then they die. Perennial plants in deserts are characterized by adaptations that conserve water: deep roots, reduced foliage, and water-storing stems (Figure 20.3.4). Seed plants in the desert produce seeds that can lie dormant for extended periods between rains. Most animal life in subtropical deserts has adapted to a nocturnal life, spending the hot daytime hours beneath the ground. The Namib Desert is the oldest on the planet, and has probably been dry for more than 55 million years. It supports a number of endemic species (species found only there) because of this great age. For example, the unusual gymnosperm Welwitschia mirabilis is the only extant species of an entire order of plants. There are also five species of reptiles considered endemic to the Namib.

In addition to subtropical deserts there are cold deserts that experience freezing temperatures during the winter and any precipitation is in the form of snowfall. The largest of these deserts are the Gobi Desert in northern China and southern Mongolia, the Taklimakan Desert in western China, the Turkestan Desert, and the Great Basin Desert of the United States.

Chaparral

The chaparral is also called scrub forest and is found in California, along the Mediterranean Sea, and along the southern coast of Australia (Figure 20.3.1). 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 maintenance of this biome and frequently threatens human habitation in this biome in the U.S. (Figure 20.3.5).

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 (Figure 20.3.1). 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 (Figure 20.3.6). 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.

Fires, 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 enhanced 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.

Temperate Forests

Temperate forests are the most common biome in eastern North America, Western Europe, Eastern Asia, Chile, and New Zealand (Figure 20.3.1). This biome is found throughout mid-latitude regions. 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. Thus, 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.

The 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 (Figure 20.3.7).

Boreal Forests

The boreal forest, also known as taiga or coniferous forest, is found roughly between 50o and 60o north latitude across most of Canada, Alaska, Russia, and northern Europe (Figure 20.3.1). Boreal forests are also found above a certain elevation (and below high elevations where trees cannot grow) 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 broad leaf. 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.

The net primary productivity of boreal forests is lower than that of temperate forests and tropical wet forests. The 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, 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 (Figure 20.3.8).

Arctic Tundra

The Arctic tundra lies north of the subarctic boreal forests and is located throughout the Arctic regions of the Northern Hemisphere (Figure 20.3.1). 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. However, 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. And, as in the boreal forests, there is little evaporation 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 (Figure 20.3.9). 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.

CONCEPT IN ACTION

Watch this Assignment Discovery: Biomes video for an overview of biomes. To explore further, select one of the biomes on the extended playlist: desert, savanna, temperate forest, temperate grassland, tropic, tundra.

Section Summary

Earth has terrestrial and aquatic biomes. 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.

Multiple Choice

Which of the following biomes is characterized by abundant water resources?

A. deserts
B. boreal forests
C. savanna
D. tropical wet forests

D

Which of the following biomes is characterized by short growing seasons?

A. tropical wet forests
C. Arctic tundra
D. savanna

C

Why is the tundra treeless?

A. lack of sufficient water
B. permanently frozen ground
C. winters too harsh
D. too many fires

B

Free Response

The extremely low precipitation of subtropical desert biomes might lead one to expect fire to be a major disturbance factor; however, fire is more common in the temperate grassland biome than in the subtropical desert biome. Why is this?

Fire is less common in desert biomes than in temperate grasslands because deserts have low net primary productivity, thus very little plant biomass to fuel a fire.

In what ways are the subtropical desert and the Arctic tundra similar?

Both the subtropical desert and the Arctic tundra have a low supply of water. In the desert, this is due to extremely low precipitation, and in the Arctic tundra, much of the water is unavailable to plants because it is frozen. Both the subtropical desert and the Arctic tundra have low net primary productivity.

Glossary

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
savanna
a biome located in the tropics with an extended dry season and characterized by a grassland with sparsely distributed trees
subtropical desert
a biome found in the subtropics with hot daily temperatures, very low and unpredictable precipitation, and characterized by a limited dry-adapted vegetation
temperate forest
a biome found in temperate regions with moderate rainfall and dominated structurally by deciduous trees
temperate grassland
a biome dominated by grasses and herbaceous plants due to low precipitation, periodic fires, and grazing

Terrestrial Biomes

If you look at these two pictures, you will see very few similarities. The picture on the left shows a desert in Africa. The picture on the right shows a rainforest in Australia. The desert doesn’t have any visible plants, whereas the rainforest is densely packed with trees. Do they have different climates? Does one get more rain than the other?


Terrestrial Biomes

The Earth’s biomes are categorized into two major groups: terrestrial and aquatic. Terrestrial biomes are based on land, while aquatic biomes include both ocean and freshwater biomes. The eight major terrestrial biomes on Earth are each distinguished by characteristic temperatures and amount of precipitation. Comparing the annual totals of precipitation and fluctuations in precipitation from one biome to another provides clues as to the importance of abiotic factors in the distribution of biomes. Temperature variation on a daily and seasonal basis is also important for predicting the geographic distribution of the biome and the vegetation type in the biome. The distribution of these biomes shows that the same biome can occur in geographically distinct areas with similar climates ([link]).

Which of the following statements about biomes is false?

  1. Chaparral is dominated by shrubs.
  2. Savannas and temperate grasslands are dominated by grasses.
  3. Boreal forests are dominated by deciduous trees.
  4. Lichens are common in the arctic tundra.

Tropical Wet Forest

Tropical wet forests are also referred to as tropical rainforests. This biome is found in equatorial regions ([link]). The vegetation is characterized by plants with broad leaves that fall off throughout the year. Unlike the trees of deciduous forests, the trees in this biome do not have a seasonal loss of leaves associated with variations in temperature and sunlight these forests are “evergreen” year-round.

The temperature and sunlight profiles of tropical wet forests are very stable in comparison to that of other terrestrial biomes, with the temperatures ranging from 20 °C to 34 °C (68 °F to 93 °F). When one compares the annual temperature variation of tropical wet forests with that of other forest biomes, the lack of seasonal temperature variation in the tropical wet forest becomes apparent. This lack of seasonality leads to year-round plant growth, rather than the seasonal (spring, summer, and fall) growth seen in other biomes. In contrast to other ecosystems, tropical ecosystems do not have long days and short days during the yearly cycle. Instead, a constant daily amount of sunlight (11–12 hrs per day) provides more solar radiation, thereby, a longer period of time for plant growth.

The annual rainfall in tropical wet forests ranges from 125 to 660 cm (50–200 in) with some monthly variation. While sunlight and temperature remain fairly consistent, annual rainfall is highly variable. Tropical wet forests 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. However, the driest month of a tropical wet forest still exceeds the annual rainfall of some other biomes, such as deserts.

Tropical wet forests have high net primary productivity because the annual temperatures and precipitation values in these areas are ideal for plant growth. Therefore, the extensive biomass present in the tropical wet forest leads to plant communities with very high species diversities ([link]). Tropical wet forests have more species of trees than any other biome on average between 100 and 300 species of trees are present in a single hectare (2.5 acres) of South America. One way to visualize this is to compare the distinctive horizontal layers within the tropical wet forest biome. 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, fungi, animals, and other organisms within the tropical wet forests. For instance, epiphytes are plants that grow on other plants, which typically are not harmed. Epiphytes are found throughout tropical wet forest biomes. 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 and have adapted to this arboreal lifestyle.

Savannas

Savannas are grasslands with scattered trees, and they are located in Africa, South America, and northern Australia ([link]). Savannas are hot, tropical areas with temperatures averaging from 24 °C to 29 °C (75 °F to 84 °F) and an annual rainfall of 10–40 cm (3.9–15.7 in). Savannas have an extensive dry season for this reason, forest trees do not grow as well as they do in the tropical wet forest (or other forest biomes). As a result, within the grasses and forbs (herbaceous flowering plants) that dominate the savanna, there are relatively few trees ([link]). 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.

Subtropical Deserts

Subtropical deserts exist between 15 ° and 30 ° north and south latitude and are centered on the Tropics of Cancer and Capricorn ([link]). This biome is very dry in some years, evaporation exceeds precipitation. Subtropical hot deserts can have daytime soil surface temperatures above 60 °C (140 °F) and nighttime temperatures approaching 0 °C (32 °F). In cold deserts, temperatures can be as high as 25 °C and can drop below -30 °C (-22 °F). Subtropical deserts are characterized by low annual precipitation of fewer than 30 cm (12 in) with little monthly variation and lack of predictability in rainfall. In some cases, the annual rainfall can be as low as 2 cm (0.8 in) in subtropical deserts located in central Australia (“the Outback”) and northern Africa.

The vegetation and low animal diversity of this biome is closely related to this low and unpredictable precipitation. Very dry deserts lack perennial vegetation that lives from one year to the next instead, many plants are annuals that grow quickly and reproduce when rainfall does occur, then they die. Many other plants in these areas are characterized by having a number of adaptations that conserve water, such as deep roots, reduced foliage, and water-storing stems ([link]). Seed plants in the desert produce seeds that can be in dormancy for extended periods between rains. Adaptations in desert animals include nocturnal behavior and burrowing.

Chaparral

The chaparral is also called the scrub forest and is found in California, along the Mediterranean Sea, and along the southern coast of Australia ([link]). 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, shown in [link], is dominated by shrubs and is adapted to periodic fires, with some plants producing seeds that only germinate 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.

Temperate Grasslands

Temperate grasslands are found throughout central North America, where they are also known as prairies they are also in Eurasia, where they are known as steppes ([link]). 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 and when ample water is available, which occurs in the spring, summer, and fall. During much of the winter, temperatures are low, and water, which is stored in the form of ice, is not available for plant growth.

Annual precipitation ranges from 25 cm to 75 cm (9.8–29.5 in). Because of relatively lower annual precipitation in temperate grasslands, there are few trees except for those found growing along rivers or streams. The dominant vegetation tends to consist of grasses and some prairies sustain populations of grazing animals [link]. 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.

Fires, mainly caused by lightning, are a natural disturbance in temperate grasslands. 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.

Temperate Forests

Temperate forests are the most common biome in eastern North America, Western Europe, Eastern Asia, Chile, and New Zealand ([link]). This biome is found throughout mid-latitude regions. Temperatures range between -30 °C and 30 °C (-22 °F to 86 °F) 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).

Because of the moderate annual rainfall and temperatures, deciduous trees are the dominant plant in this biome ([link]). Deciduous trees lose their leaves each fall and remain leafless in the winter. Thus, no photosynthesis occurs in the deciduous trees during the dormant winter period. Each spring, new leaves appear as the temperature increases. Because of the dormant period, the net primary productivity of temperate forests is less than that of tropical wet forests. In addition, temperate forests show less diversity of tree species than tropical wet forest biomes.

The trees of the temperate forests leaf out and shade much of the ground however, this biome is more open than tropical wet forests because trees in the temperate forests do not grow as tall as the trees in tropical wet forests. The soils of the temperate forests are rich in inorganic and organic nutrients. This is due to the thick layer of leaf litter on forest floors. 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 (such as the pill bug or roly-poly, Armadillidium vulgare) and their predators, such as the red-backed salamander (Plethodon cinereus).

Boreal Forests

The boreal forest, also known as taiga or coniferous forest, is found south of the Arctic Circle and across most of Canada, Alaska, Russia, and northern Europe ([link]). 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 broad leaf. This benefits evergreen trees, which 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 may have a competitive advantage over the broad-leafed deciduous trees.

The net primary productivity of boreal forests is lower than that of temperate forests and tropical wet forests. The aboveground biomass of boreal forests is high because these slow-growing tree species are long lived and accumulate standing biomass over time. Plant species diversity is less than that seen in temperate forests and tropical wet forests. Boreal forests lack the pronounced elements of the layered forest structure seen in tropical wet forests. The structure of a boreal forest is often only a tree layer and a ground layer ([link]). When conifer needles are dropped, they decompose more slowly than broad leaves therefore, fewer nutrients are returned to the soil to fuel plant growth.

Arctic Tundra

The Arctic tundra lies north of the subarctic boreal forest and is located throughout the Arctic regions of the northern hemisphere ([link]). The average winter temperature is -34 °C (-34 °F) and the average summer temperature is from 3 °C to 12 °C (37 °F–52 °F). Plants in the arctic tundra have a very short growing season of approximately 10–12 weeks. However, during this time, there are almost 24 hours of daylight and plant growth is rapid. The annual precipitation of the Arctic tundra is very low with little annual variation in precipitation. And, as in the boreal forests, there is little evaporation due to the cold temperatures.

Plants in the Arctic tundra are generally low to the ground ([link]). 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 deep into the soil and slows the decay of organic matter, which inhibits the release of nutrients from organic matter. During the growing season, the ground of the Arctic tundra can be completely covered with plants or lichens.

Watch this Assignment Discovery: Biomes video for an overview of biomes. To explore further, select one of the biomes on the extended playlist: desert, savanna, temperate forest, temperate grassland, tropic, tundra.

Section Summary

The Earth has terrestrial biomes and aquatic biomes. Aquatic biomes include both freshwater and marine environments. There are eight major terrestrial biomes: tropical wet forests, 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 weather and hot weather alternating throughout the year. In warm, moist biomes, such as the tropical wet forest, 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 available water.

Art Connections

[link] Which of the following statements about biomes is false?

  1. Chaparral is dominated by shrubs.
  2. Savannas and temperate grasslands are dominated by grasses.
  3. Boreal forests are dominated by deciduous trees.
  4. Lichens are common in the arctic tundra.

[link] C. Boreal forests are not dominated by deciduous trees.

Review Questions

Which of the following biomes is characterized by abundant water resources?

Which of the following biomes is characterized by short growing seasons?

Free Response

The extremely low precipitation of subtropical desert biomes might lead one to expect fire to be a major disturbance factor however, fire is more common in the temperate grassland biome than in the subtropic desert biome. Why is this?

Fire is less common in desert biomes than in temperate grasslands because deserts have low net primary productivity and, thus, very little plant biomass to fuel a fire.

In what ways are the subtropical desert and the arctic tundra similar?

Both the subtropical desert and the arctic tundra have a low supply of water. In the desert, this is due to extremely low precipitation, and in the arctic tundra, much of the water is unavailable to plants because it is frozen. Both the subtropical desert and the arctic tundra have low net primary productivity.

Glossary


28.3: Terrestrial Biomes - Biology

By the end of this section, you will be able to do the following:

  • Identify the two major abiotic factors that determine terrestrial biomes
  • Recognize distinguishing characteristics of each of the eight major terrestrial biomes

The Earth’s biomes are categorized into two major groups: terrestrial and aquatic. Terrestrial biomes are based on land, while aquatic biomes include both ocean and freshwater biomes. The eight major terrestrial biomes on Earth are each distinguished by characteristic temperatures and amount of precipitation. Comparing the annual totals of precipitation and fluctuations in precipitation from one biome to another provides clues as to the importance of abiotic factors in the distribution of biomes. Temperature variation on a daily and seasonal basis is also important for predicting the geographic distribution of the biome and the vegetation type in the biome. The distribution of these biomes shows that the same biome can occur in geographically distinct areas with similar climates ((Figure)).

Art Connection

Figure 1. Each of the world’s major biomes is distinguished by characteristic temperatures and amounts of precipitation. Polar ice and mountains are also shown.

Which of the following statements about biomes is false?

  1. Chaparral is dominated by shrubs.
  2. Savannas and temperate grasslands are dominated by grasses.
  3. Boreal forests are dominated by deciduous trees.
  4. Lichens are common in the arctic tundra.

C. Boreal forests are not dominated by deciduous trees.

Tropical Wet Forest

Tropical wet forests are also referred to as tropical rainforests. This biome is found in equatorial regions ((Figure)). The vegetation is characterized by plants with broad leaves that fall and are replaced throughout the year. Unlike the trees of deciduous forests, the trees in this biome do not have a seasonal loss of leaves associated with variations in temperature and sunlight these forests are “evergreen” year-round.

The temperature and sunlight profiles of tropical wet forests are very stable in comparison to that of other terrestrial biomes, with the temperatures ranging from 20 °C to 34 °C (68 °F to 93 °F). When one compares the annual temperature variation of tropical wet forests with that of other forest biomes, the lack of seasonal temperature variation in the tropical wet forest becomes apparent. This lack of seasonality leads to year-round plant growth, rather than the seasonal (spring, summer, and fall) growth seen in other more temperate biomes. In contrast to other ecosystems, tropical ecosystems do not have long days and short days during the yearly cycle. Instead, a constant daily amount of sunlight (11–12 hrs per day) provides more solar radiation, thereby, a longer period of time for plant growth.

The annual rainfall in tropical wet forests ranges from 125 cm to 660 cm (50–200 in) with some monthly variation. While sunlight and temperature remain fairly consistent, annual rainfall is highly variable. Tropical wet forests typically 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. However, the driest month of a tropical wet forest still exceeds the annual rainfall of some other biomes, such as deserts.

Tropical wet forests have high net primary productivity because the annual temperatures and precipitation values in these areas are ideal for plant growth. Therefore, the extensive biomass present in the tropical wet forest leads to plant communities with very high species diversities ((Figure)). Tropical wet forests have more species of trees than any other biome on average between 100 and 300 species of trees are present in a single hectare (2.5 acres) of South American Amazonian rain forest. One way to visualize this is to compare the distinctive horizontal layers within the tropical wet forest biome. 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, fungi, animals, and other organisms within the tropical wet forests.

For example, epiphytes are plants that grow on other plants, which typically are not harmed. Epiphytes are found throughout tropical wet forest biomes. 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 and have adapted to this arboreal lifestyle.

Figure 2. Tropical wet forests, such as these forests along the Madre de Dios river, Peru, near the Amazon River, have high species diversity. (credit: Roosevelt Garcia)

Savannas

Savannas are grasslands with scattered trees, and they are located in Africa, South America, and northern Australia ((Figure)). Savannas are usually hot, tropical areas with temperatures averaging from 24 °C to 29 °C (75 °F to 84 °F) and an annual rainfall of 10–40 cm (3.9–15.7 in). Savannas have an extensive dry season for this reason, forest trees do not grow as well as they do in the tropical wet forest (or other forest biomes). As a result, within the grasses and forbs (herbaceous flowering plants) that dominate the savanna, there are relatively few trees ((Figure)). Since fire is an important source of disturbance in this biome, plants have evolved well-developed root systems that allow them to quickly resprout after a fire.

Figure 3. Savannas, like this one in Taita Hills Wildlife Sanctuary in Kenya, are dominated by grasses. (credit: Christopher T. Cooper)

Subtropical Deserts

Subtropical deserts exist between 15° and 30° north and south latitude and are centered on the Tropics of Cancer and Capricorn ((Figure)). This biome is very dry in some years, evaporation exceeds precipitation. Subtropical hot deserts can have daytime soil surface temperatures above 60 °C (140 °F) and nighttime temperatures approaching 0 °C (32 °F). This is largely due to the lack of atmospheric water. In cold deserts, temperatures can be as high as 25 °C and can drop below -30 °C (-22 °F). Subtropical deserts are characterized by low annual precipitation of fewer than 30 cm (12 in) with little monthly variation and lack of predictability in rainfall. In some cases, the annual rainfall can be as low as 2 cm (0.8 in) in subtropical deserts located in central Australia (“the Outback”) and northern Africa.

The vegetation and low animal diversity of this biome is closely related to low and unpredictable precipitation. Very dry deserts lack perennial vegetation that lives from one year to the next instead, many plants are annuals that grow quickly and reproduce when rainfall does occur, and then die. Many other plants in these areas are characterized by having a number of adaptations that conserve water, such as deep roots, reduced foliage, and water-storing stems ((Figure)). Seed plants in the desert produce seeds that can be in dormancy for extended periods between rains. Adaptations in desert animals include nocturnal behavior and burrowing.

Figure 4. To reduce water loss, many desert plants have tiny leaves or no leaves at all. The leaves of ocotillo (Fouquieria splendens), shown here in the Sonora Desert near Gila Bend, Arizona, appear only after rainfall, and then are shed.

Chaparral

The chaparral is also called the scrub forest and is found in California, along the Mediterranean Sea, and along the southern coast of Australia ((Figure)). 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, shown in (Figure), is dominated by shrubs adapted to periodic fires, with some plants producing seeds that only germinate 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.

Figure 5. The chaparral is dominated by shrubs. (credit: Miguel Vieira)

Temperate Grasslands

Temperate grasslands are found throughout central North America, where they are also known as prairies they are also in Eurasia, where they are known as steppes ((Figure)). 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 and when ample water is available, which occurs in the spring, summer, and fall. During much of the winter, temperatures are low, and water, which is stored in the form of ice, is not available for plant growth.

Annual precipitation ranges from 25 cm to 75 cm (9.8–29.5 in). Because of relatively lower annual precipitation in temperate grasslands, there are few trees except for those found growing along rivers or streams. The dominant vegetation tends to consist of grasses dense enough to sustain populations of grazing animals (Figure). 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.

Figure 6. The American bison (Bison bison), more commonly called the buffalo, is a grazing mammal that once populated American prairies in huge numbers. (credit: Jack Dykinga, USDA Agricultural Research Service)

Fires, mainly caused by lightning, are a natural disturbance in temperate grasslands. When fire is suppressed in temperate grasslands, the vegetation eventually converts to scrub and sometimes dense forests with drought-tolerant tree species. Often, the restoration or management of temperate grasslands requires the use of controlled burns to suppress the growth of trees and maintain the grasses.

Temperate Forests

Temperate forests are the most common biome in eastern North America, Western Europe, Eastern Asia, Chile, and New Zealand ((Figure)). This biome is found throughout mid-latitude regions. Temperatures range between -30 °C and 30 °C (-22 °F to 86 °F) and drop to below freezing periodically during cold winters. 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).

Because of the moderate annual rainfall and temperatures, deciduous trees are the dominant plant in this biome ((Figure)). Deciduous trees lose their leaves each fall and remain leafless in the winter. Thus, no photosynthesis occurs in the deciduous trees during the dormant winter period. Each spring, new leaves appear as the temperature increases. Because of the dormant period, the net primary productivity of temperate forests is less than that of tropical wet forests. In addition, temperate forests show less diversity of tree species than tropical wet forest biomes.

Figure 7. Deciduous trees are the dominant plant in the temperate forest. (credit: Oliver Herold)

The trees of the temperate forests leaf out and shade much of the ground however, this biome is more open than tropical wet forests because most trees in the temperate forests do not grow as tall as the trees in tropical wet forests. The soils of the temperate forests are rich in inorganic and organic nutrients. This is due to the thick layer of leaf litter on forest floors, which does not develop in tropical rainforests. 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 (such as the pill bug or roly-poly, Armadillidium vulgare) and their predators, such as the red-backed salamander (Plethodon cinereus).

Boreal Forests

The boreal forest, also known as taiga or coniferous forest, is found south of the Arctic Circle and across most of Canada, Alaska, Russia, and northern Europe ((Figure)). 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 (coniferous) 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 broad leaf. This benefits evergreen trees, which 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 may have a competitive advantage over the broad-leafed deciduous trees.

The net primary productivity of boreal forests is lower than that of temperate forests and tropical wet forests. The above-ground biomass of boreal forests is high because these slow-growing tree species are long-lived and accumulate a large standing biomass over time. Plant species diversity is less than that seen in temperate forests and tropical wet forests. Boreal forests lack the pronounced elements of the layered forest structure seen in tropical wet forests. The structure of a boreal forest is often only a tree layer and a ground layer ((Figure)). When conifer needles are dropped, they decompose more slowly than broad leaves therefore, fewer nutrients are returned to the soil to fuel plant growth.

Figure 8. The boreal forest (taiga) has low lying plants and conifer trees. (credit: L.B. Brubaker)

Arctic Tundra

The Arctic tundra lies north of the subarctic boreal forest and is located throughout the Arctic regions of the northern hemisphere ((Figure)). The average winter temperature is -34 °C (29.2 °F) and the average summer temperature is from 3 °C to 12 °C (37 °F–52 °F). Plants in the arctic tundra have a very short growing season of approximately 10–12 weeks.

However, during this time, there are almost 24 hours of daylight and plant growth is rapid. The annual precipitation of the Arctic tundra is very low with little annual variation in precipitation. And, as in the boreal forests, there is little evaporation due to the cold temperatures.

Plants in the Arctic tundra are generally low to the ground ((Figure)). There is little species diversity, low net primary productivity, and low above-ground 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 deep into the soil and slows the decay of organic matter, which inhibits the release of nutrients from organic matter. During the growing season, the ground of the Arctic tundra can be completely covered with plants or lichens.

Figure 9. Low-growing plants such as shrub willow dominate the tundra landscape, shown here in the Arctic National Wildlife Refuge. (credit: USFWS Arctic National Wildlife Refuge)

Link to Learning

Watch this Assignment Discovery: Biomes video for an overview of biomes. To explore further, select one of the biomes on the extended playlist: desert, savanna, temperate forest, temperate grassland, tropic, tundra.

Section Summary

The Earth has terrestrial biomes and aquatic biomes. Aquatic biomes include both freshwater and marine environments. There are eight major terrestrial biomes: tropical wet forests, 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 weather and hot weather alternating throughout the year. In warm, moist biomes, such as the tropical wet forest, net primary productivity is high, as warm temperatures, abundant water, and a year-round growing season fuel plant growth and supply energy for high diversity throughout the food web. Other biomes, such as deserts and tundras, have low primary productivity due to extreme temperatures and a shortage of available water.

Art Connections

(Figure) Which of the following statements about biomes is false?

  1. Chaparral is dominated by shrubs.
  2. Savannas and temperate grasslands are dominated by grasses.
  3. Boreal forests are dominated by deciduous trees.
  4. Lichens are common in the arctic tundra.

(Figure) C. Boreal forests are not dominated by deciduous trees.

Review Questions

Which of the following biomes is characterized by abundant water resources?

Which of the following biomes is characterized by short growing seasons?

Free Response

The extremely low precipitation of subtropical desert biomes might lead one to expect fire to be a major disturbance factor however, fire is more common in the temperate grassland biome than in the subtropical desert biome. Why is this?

Fire is less common in desert biomes than in temperate grasslands because deserts have low net primary productivity and, thus, very little plant biomass to fuel a fire.

In what ways are the subtropical desert and the arctic tundra similar?

Both the subtropical desert and the arctic tundra have a low supply of water. In the desert, this is due to extremely low precipitation, and in the arctic tundra, much of the water is unavailable to plants because it is frozen. Both the subtropical desert and the arctic tundra have low net primary productivity.


ALEX Lesson Plan

This is a technology-based Biology lesson on the Biomes of the world. Students will work in groups and research their designated terrestrial biome. Students will research abiotic and biotic factors about their biome. Students will create a digital presentation of their biome using Haiku Deck. The presentation will summarize how the abiotic and biotic factors interact in their biome. Students will then use the collected data from the presentations to create food chains and food webs for their designated biomes.

This lesson plan results from a collaboration between the Alabama State Department of Education and ASTA.

  • Use observations to develop a model that illustrates ecological hierarchies and compare developed model to hierarchies existing in nature.
  • Use models to investigate the role of different environmental factors within the hierarchy.
  • Use data to develop a model depicting the ecological hierarchy of a novel ecosystem and communicate the dynamics of the hierarchy.
  • Investigate biomes, using a variety of resources to compare and contrast the characteristics of each.
  • Use evidence to classify major geographical regions into biomes, based on climate and dominant life forms.
  • Ecology
  • Biosphere
  • Biotic factor
  • Abiotic factor
  • Population
  • Biological community
  • Ecosystem
  • Biome
  • Species
  • The biosphere is the portion of the Earth that supports life.
  • The lowest level of organization is the individual organism itself.
  • Individual organisms of a single species that share the same geographical location at the same time make up the population.
  • A group of interacting populations that occupy the same geographical area at the same time is a biological community.
  • An ecosystem is the biological community and all the abiotic factors that affect it (e.g., water temperature, light availability).
  • A biome is a large group of ecosystems that share the same climate and have similar types of communities.
  • Organize objects or organisms into levels of hierarchy.
  • Develop a hierarchical classification model using standard language and parameters.
  • In order to study relationships within the biosphere, it is divided into smaller levels of organization.
  • The simplest level of organization is the organism, with increasing levels of complexity as the numbers and interactions between organisms increase, shown in the population, biological community, ecosystem, and biome until reaching the most complex level of the biosphere.
  • Categorize organisms in an ecosystem based on evidence of how they obtain energy.
  • Construct a food chain that differentiates between producers, primary, secondary and tertiary consumers and integrate multiple food chains into a food web.
  • Use relationships between organisms to develop a food web and use it to demonstrate flow of energy and predict the impacts of population changes. Construct a pyramid of biomass, given population data about organisms in the ecosystem and make calculations using data from the pyramid.
  • Use mathematical examples, such as the 10% law to explain why there is less energy available at each level of an energy pyramid.
  • Analyze data to identify patterns in the cycling of carbon, nitrogen and water in ecosystems.
  • Use patterns identified in the cycling of carbon, nitrogen, and water to build models of matter cycling through ecosystems.
  • Predict the effect of the reduction of a population of species on the carbon, nitrogen or water cycle.
  • Autotroph
  • Heterotroph
  • Primary producer
  • Primary consumer
  • Secondary consumer
  • Tertiary consumer
  • Herbivore
  • Carnivore
  • Omnivore
  • Detritivore
  • Trophic levels: primary, secondary and tertiary
  • Food chain
  • Food web
  • Biomass
  • Energy pyramid
  • Biomass pyramid
  • Number pyramid
  • Matter
  • Nutrient
  • Biogeochemical cycle
  • Nitrogen fixation
  • Denitrification
  • Law of conservation of mass
  • A food chain is a simple model representing the transfer of energy from organism to organism (e.g., sun &rarr plant &rarr grasshopper &rarr mouse &rarr snake).
  • Each step of a food chain represents a trophic level always starting with an autotroph in the first level and heterotrophs in the remaining levels.
  • The overlapping relationships between multiple food chains are shown in a food web.
  • An ecological pyramid is a model that can show the relative amounts of energy, biomass, or numbers of organisms at each trophic level in an ecosystem.
  • In an energy pyramid, only 10% of energy is passed from one trophic level to the next due to loss of energy in the form of heat caused by cellular respiration (10% rule).
  • In a biomass pyramid, the total mass of living matter at each trophic level tends to decrease.
  • In a numbers pyramid, it shows the number of organisms at each trophic level tends to decrease because there is less energy available to support organisms.
  • The exchange of matter through the biosphere is called the biogeochemical cycle and involves living organisms (bio), geological processes (geo), and chemical processes (chemical).
  • Use a self-created food web diagram to predict the impact of removing one organism on other organisms within the food web.
  • Use data to create ecological pyramids to show flow of energy, biomass and number of organisms.
  • Model the cycling of matter (e.g., Carbon, water, nitrogen) through the biosphere.
  • Combine a food web diagram with a matter cycling diagram to provide a holistic view of the many aspects that make up an ecosystem.
  • Everything in an ecosystem is connected to everything else (both abiotic and biotic), either directly or indirectly.
  • Nutrients, in the form of elements and compounds, flow through organisms in an ecosystem (e.g., grass captures substances from the air, soil and water and converts them into usable nutrients &rarr cow eats the grass &rarr human eats the cow &rarr decomposers return the nutrients to the cycle at every level).

Local/National Standards:

Primary Learning Objective(s):

Additional Learning Objective(s):

The students will use technology as a tool to research, evaluate, and communicate information to others using a digital presentation.

Total Duration:

Materials and Resources:

Discuss with students the definition of a Biome. Make student copies of the Biome worksheet for students to take notes on during presentations.

Biome- a large region characterized by a specific type of climate and certain types of plants and animals.

Make student copies or group copies of the rubric and discuss with the class before the project begins.

Technology Resources Needed:

Interactive whiteboard to model research and/ Haiku Deck for digital presentations.

Student computers to research the approved websites for their Biomes.

Background/Preparation:

Make student copies or group copies of the rubric and discuss with the class before the project begins.

The teacher should create a free account in Haiku Deck. This software is very easy to manipulate. If you click on the help button in the upper right-hand corner, it labels all the buttons for you and shows you the options. If you select Gallery on the home screen, students can look at Decks that have been created and look at presentation templates. I would suggest that the teacher creates a sample Deck with the students on the whiteboard. The students will also need to create a free public account if they want to use Haiku Deck.

Give students the Biome Worksheet to take notes on the day of the presentations.

Before/Engage

Step 1- Show the video about Biomes.

This video introduces the viewer/student to the Biomes of Earth. It is designed as a motivational "trailer" to be shown by teachers in elementary school and Biology and Ecology classrooms in middle school, high school and college as a visual introduction to the many types of places that life calls home.

During/Explore/Explain

Research (2 days)

Assign students to cooperative learning groups of four members. Assign each group one of the terrestrial biomes from the list below.

Tundra, Taiga, Temperate Forest, Tropical Forest, Temperate Grassland, Savanna, Chaparral, and Desert.

The students should find out the following on their Biome.

4. The climate of their biome including precipitation and temperature.

Step 2 - Students should research general information about their assigned biome. Students should also find difference pictures of their assigned biomes.

Give students these three websites to begin their research

Step 4 - After students have gathered their research, the students will create a digital presentation. Students will create a free public account at Haiku Deck.

After the presentations have been created, have each group share their Haiku Deck with the class on the Interactive White Board. While presentations are being made, the students should take notes on their Biome Worksheet.

Biome groups will present their digital presentation to the class.

After/Explain/Extend

The students can complete the Biome Quiz at the end of the presentations and then create a travel brochure highlighting the abiotic and biotic factors of their biome as an extension.

Assessment Strategies

Students can be assessed multiple times during the day by monitoring their research and notes taken during the class period.

The Biome note taking worksheet should be graded on completion. The students will be graded on their digital presentation using the rubric provided.

The students can be assessed on the Biome Quiz at the end of the lesson.

Acceleration:

In addition to the digital presentation in Haiku Deck of their biome, students could create a travel brochure convincing tourists to plan a trip to their biome.

Intervention:

Grouping students based on academic strengths and weaknesses will help them in creating their digital presentation and with the research.


Biomes established by altitude

Temperature is the major influence on the biomes discussed above. Because temperatures decline with altitude as well as latitude, similar biomes exist on mountains even when they are at low latitudes. As a rule of thumb, a climb of 1000 feet (about 300 m) is equivalent in changed flora and fauna to a trip northward of some 600 miles (966 km).

The photo is of alpine tundra at 12,000 feet (3,658 m) in the Rocky Mountains.


Field studies in various parts of the Northern Hemisphere have shown that in recent decades many species of animals and plants have

  • shifted their ranges farther north (averagiing 16.9 kilometers per decade)
  • shifted their ranges higher in the mountains (averaging 11.0 meters per decade) .

These observations add to the growing body of evidence that global warming is affecting a broad assortment of living things.


Contents

The term was suggested in 1916 by Clements, originally as a synonym for biotic community of Möbius (1877). [4] Later, it gained its current definition, based on earlier concepts of phytophysiognomy, formation and vegetation (used in opposition to flora), with the inclusion of the animal element and the exclusion of the taxonomic element of species composition. [5] [6] In 1935, Tansley added the climatic and soil aspects to the idea, calling it ecosystem. [7] [8] The International Biological Program (1964–74) projects popularized the concept of biome. [9]

However, in some contexts, the term biome is used in a different manner. In German literature, particularly in the Walter terminology, the term is used similarly as biotope (a concrete geographical unit), while the biome definition used in this article is used as an international, non-regional, terminology—irrespectively of the continent in which an area is present, it takes the same biome name—and corresponds to his "zonobiome", "orobiome" and "pedobiome" (biomes determined by climate zone, altitude or soil). [10]

In Brazilian literature, the term "biome" is sometimes used as synonym of "biogeographic province", an area based on species composition (the term "floristic province" being used when plant species are considered), or also as synonym of the "morphoclimatic and phytogeographical domain" of Ab'Sáber, a geographic space with subcontinental dimensions, with the predominance of similar geomorphologic and climatic characteristics, and of a certain vegetation form. Both include many biomes in fact. [5] [11] [12]

To divide the world into a few ecological zones is difficult, notably because of the small-scale variations that exist everywhere on earth and because of the gradual changeover from one biome to the other. Their boundaries must therefore be drawn arbitrarily and their characterization made according to the average conditions that predominate in them. [13]

A 1978 study on North American grasslands [14] found a positive logistic correlation between evapotranspiration in mm/yr and above-ground net primary production in g/m 2 /yr. The general results from the study were that precipitation and water use led to above-ground primary production, while solar irradiation and temperature lead to below-ground primary production (roots), and temperature and water lead to cool and warm season growth habit. [15] These findings help explain the categories used in Holdridge's bioclassification scheme (see below), which were then later simplified by Whittaker. The number of classification schemes and the variety of determinants used in those schemes, however, should be taken as strong indicators that biomes do not fit perfectly into the classification schemes created.

Holdridge (1947, 1964) life zones Edit

In 1947, the American botanist and climatologist Leslie Holdridge classified climates based on the biological effects of temperature and rainfall on vegetation under the assumption that these two abiotic factors are the largest determinants of the types of vegetation found in a habitat. Holdridge uses the four axes to define 30 so-called "humidity provinces", which are clearly visible in his diagram. While this scheme largely ignores soil and sun exposure, Holdridge acknowledged that these were important.

Allee (1949) biome-types Edit

The principal biome-types by Allee (1949): [16]

Kendeigh (1961) biomes Edit

The principal biomes of the world by Kendeigh (1961): [17]

  • Terrestrial forest
  • Tropical savanna forest
  • Oceanic plankton and nekton
  • Balanoid-gastropod-thallophyte -annelid reef

Whittaker (1962, 1970, 1975) biome-types Edit

Whittaker classified biomes using two abiotic factors: precipitation and temperature. His scheme can be seen as a simplification of Holdridge's more readily accessible, but missing Holdridge's greater specificity.

Whittaker based his approach on theoretical assertions and empirical sampling. He had previously compiled a review of biome classifications. [18]

Key definitions for understanding Whittaker's scheme Edit

    : the apparent characteristics, outward features, or appearance of ecological communities or species.
  • Biome: a grouping of terrestrial ecosystems on a given continent that is similar in vegetation structure, physiognomy, features of the environment and characteristics of their animal communities. : a major kind of community of plants on a given continent.
  • Biome-type: grouping of convergent biomes or formations of different continents, defined by physiognomy.
  • Formation-type: a grouping of convergent formations.

Whittaker's distinction between biome and formation can be simplified: formation is used when applied to plant communities only, while biome is used when concerned with both plants and animals. Whittaker's convention of biome-type or formation-type is a broader method to categorize similar communities. [19]

Whittaker's parameters for classifying biome-types Edit

Whittaker used what he called "gradient analysis" of ecocline patterns to relate communities to climate on a worldwide scale. Whittaker considered four main ecoclines in the terrestrial realm. [19]

  1. Intertidal levels: The wetness gradient of areas that are exposed to alternating water and dryness with intensities that vary by location from high to low tide
  2. Climatic moisture gradient
  3. Temperature gradient by altitude
  4. Temperature gradient by latitude

Along these gradients, Whittaker noted several trends that allowed him to qualitatively establish biome-types:

  • The gradient runs from favorable to the extreme, with corresponding changes in productivity.
  • Changes in physiognomic complexity vary with how favorable of an environment exists (decreasing community structure and reduction of stratal differentiation as the environment becomes less favorable).
  • Trends in the diversity of structure follow trends in species diversity alpha and beta species diversities decrease from favorable to extreme environments.
  • Each growth-form (i.e. grasses, shrubs, etc.) has its characteristic place of maximum importance along the ecoclines.
  • The same growth forms may be dominant in similar environments in widely different parts of the world.

Whittaker summed the effects of gradients (3) and (4) to get an overall temperature gradient and combined this with a gradient (2), the moisture gradient, to express the above conclusions in what is known as the Whittaker classification scheme. The scheme graphs average annual precipitation (x-axis) versus average annual temperature (y-axis) to classify biome-types.

Biome-types Edit

  1. Tropical rainforest
  2. Tropical seasonal rainforest
    • deciduous
    • semideciduous
  3. Temperate giant rainforest
  4. Montane rainforest
  5. Temperate deciduous forest
  6. Temperate evergreen forest
    • needleleaf
    • sclerophyll
  7. Subarctic-subalpine needle-leaved forests (taiga)
  8. Elfin woodland
  9. Thorn forests and woodlands
  10. Thorn scrub
  11. Temperate woodland
  12. Temperate shrublands
    • deciduous
    • heath
    • sclerophyll
    • subalpine-needleleaf
    • subalpine-broadleaf
  13. Savanna
  14. Temperate grassland
  15. Alpine grasslands
  16. Tundra
  17. Tropical desert
  18. Warm-temperate desert
  19. Cool temperate desert scrub
  20. Arctic-alpine desert
  21. Bog
  22. Tropical fresh-water swamp forest
  23. Temperate fresh-water swamp forest
  24. Mangrove swamp
  25. Salt marsh
  26. Wetland [20]

Goodall (1974–) ecosystem types Edit

The multiauthored series Ecosystems of the world, edited by David W. Goodall, provides a comprehensive coverage of the major "ecosystem types or biomes" on earth: [21]

  1. Wet Coastal Ecosystems
  2. Dry Coastal Ecosystems
  3. Polar and Alpine Tundra
  4. Mires: Swamp, Bog, Fen, and Moor
  5. Temperate Deserts and Semi-Deserts
  6. Coniferous Forests
  7. Temperate Deciduous Forests
  8. Natural Grasslands
  9. Heathlands and Related Shrublands
  10. Temperate Broad-Leaved Evergreen Forests
  11. Mediterranean-Type Shrublands
  12. Hot Deserts and Arid Shrublands
  13. Tropical Savannas
  14. Tropical Rain Forest Ecosystems
  15. Wetland Forests
  16. Ecosystems of Disturbed Ground
  1. Managed Grasslands
  2. Field Crop Ecosystems
  3. Tree Crop Ecosystems
  4. Greenhouse Ecosystems
  5. Bioindustrial Ecosystems
  1. Intertidal and Littoral Ecosystems
  2. Coral Reefs
  3. Estuaries and Enclosed Seas
  4. Ecosystems of the Continental Shelves
  5. Ecosystems of the Deep Ocean

Walter (1976, 2002) zonobiomes Edit

The eponymously-named Heinrich Walter classification scheme considers the seasonality of temperature and precipitation. The system, also assessing precipitation and temperature, finds nine major biome types, with the important climate traits and vegetation types. The boundaries of each biome correlate to the conditions of moisture and cold stress that are strong determinants of plant form, and therefore the vegetation that defines the region. Extreme conditions, such as flooding in a swamp, can create different kinds of communities within the same biome. [10] [22] [23]

Zonobiome Zonal soil type Zonal vegetation type
ZB I. Equatorial, always moist, little temperature seasonality Equatorial brown clays Evergreen tropical rainforest
ZB II. Tropical, summer rainy season and cooler “winter” dry season Red clays or red earths Tropical seasonal forest, seasonal dry forest, scrub, or savanna
ZB III. Subtropical, highly seasonal, arid climate Serosemes, sierozemes Desert vegetation with considerable exposed surface
ZB IV. Mediterranean, winter rainy season and summer drought Mediterranean brown earths Sclerophyllous (drought-adapted), frost-sensitive shrublands and woodlands
ZB V. Warm temperate, occasional frost, often with summer rainfall maximum Yellow or red forest soils, slightly podsolic soils Temperate evergreen forest, somewhat frost-sensitive
ZB VI. Nemoral, moderate climate with winter freezing Forest brown earths and grey forest soils Frost-resistant, deciduous, temperate forest
ZB VII. Continental, arid, with warm or hot summers and cold winters Chernozems to serozems Grasslands and temperate deserts
ZB VIII. Boreal, cold temperate with cool summers and long winters Podsols Evergreen, frost-hardy, needle-leaved forest (taiga)
ZB IX. Polar, short, cool summers and long, cold winters Tundra humus soils with solifluction (permafrost soils) Low, evergreen vegetation, without trees, growing over permanently frozen soils

Schultz (1988) ecozones Edit

Schultz (1988, 2005) defined nine ecozones (note that his concept of ecozone is more similar to the concept of biome used in this article than to the concept of ecozone of BBC): [24]

  1. polar/subpolar zone
  2. boreal zone
  3. humid mid-latitudes
  4. dry mid-latitudes
  5. subtropics with winter rain
  6. subtropics with year-round rain
  7. dry tropics and subtropics
  8. tropics with summer rain
  9. tropics with year-round rain

Bailey (1989) ecoregions Edit

Robert G. Bailey nearly developed a biogeographical classification system of ecoregions for the United States in a map published in 1976. He subsequently expanded the system to include the rest of North America in 1981, and the world in 1989. The Bailey system, based on climate, is divided into seven domains (polar, humid temperate, dry, humid, and humid tropical), with further divisions based on other climate characteristics (subarctic, warm temperate, hot temperate, and subtropical marine and continental lowland and mountain). [25] [26]

  • 100 Polar Domain
    • 120 Tundra Division (Köppen: Ft)
    • M120 Tundra Division – Mountain Provinces
    • 130 Subarctic Division (Köppen: E)
    • M130 Subarctic Division – Mountain Provinces
    • 210 Warm Continental Division (Köppen: portion of Dcb)
    • M210 Warm Continental Division – Mountain Provinces
    • 220 Hot Continental Division (Köppen: portion of Dca)
    • M220 Hot Continental Division – Mountain Provinces
    • 230 Subtropical Division (Köppen: portion of Cf)
    • M230 Subtropical Division – Mountain Provinces
    • 240 Marine Division (Köppen: Do)
    • M240 Marine Division – Mountain Provinces
    • 250 Prairie Division (Köppen: arid portions of Cf, Dca, Dcb)
    • 260 Mediterranean Division (Köppen: Cs)
    • M260 Mediterranean Division – Mountain Provinces
    • 310 Tropical/Subtropical Steppe Division
    • M310 Tropical/Subtropical Steppe Division – Mountain Provinces
    • 320 Tropical/Subtropical Desert Division
    • 330 Temperate Steppe Division
    • 340 Temperate Desert Division
    • 410 Savanna Division
    • 420 Rainforest Division

    Olson & Dinerstein (1998) biomes for WWF / Global 200 Edit

    A team of biologists convened by the World Wildlife Fund (WWF) developed a scheme that divided the world's land area into biogeographic realms (called "ecozones" in a BBC scheme), and these into ecoregions (Olson & Dinerstein, 1998, etc.). Each ecoregion is characterized by a main biome (also called major habitat type). [27] [28]

    This classification is used to define the Global 200 list of ecoregions identified by the WWF as priorities for conservation. [27]

    For the terrestrial ecoregions, there is a specific EcoID, format XXnnNN (XX is the biogeographic realm, nn is the biome number, NN is the individual number).

    Biogeographic realms (terrestrial and freshwater) Edit

    • NA: Nearctic
    • PA: Palearctic
    • AT: Afrotropic
    • IM: Indomalaya
    • AA: Australasia
    • NT: Neotropic
    • OC: Oceania
    • AN: Antarctic[28]

    The applicability of the realms scheme above - based on Udvardy (1975)—to most freshwater taxa is unresolved. [29]

    Biogeographic realms (marine) Edit

    Biomes (terrestrial) Edit

      (tropical and subtropical, humid) (tropical and subtropical, semihumid) (tropical and subtropical, semihumid) (temperate, humid) (temperate, humid to semihumid) (subarctic, humid) (tropical and subtropical, semiarid) (temperate, semiarid) (temperate to tropical, fresh or brackish water inundated) (alpine or montane climate) (Arctic) or sclerophyll forests (temperate warm, semihumid to semiarid with winter rainfall) (temperate to tropical, arid) (subtropical and tropical, salt water inundated) [28]

    Biomes (freshwater) Edit

    According to the WWF, the following are classified as freshwater biomes: [31]

    • Large lakes
    • Large river deltas
    • Polar freshwaters
    • Montane freshwaters
    • Temperate coastal rivers
    • Temperate floodplain rivers and wetlands
    • Temperate upland rivers
    • Tropical and subtropical coastal rivers
    • Tropical and subtropical floodplain rivers and wetlands
    • Tropical and subtropical upland rivers
    • Xeric freshwaters and endorheic basins

    Biomes (marine) Edit

    Biomes of the coastal and continental shelf areas (neritic zone):

    Summary of the scheme Edit

        (terrestrial) (8)
          (867), each characterized by a main biome type (14)
            (biotopes)
            (freshwater) (8)
              (426), each characterized by a main biome type (12)
                (biotopes)
                Biogeographic realms (marine) (12)
                  (Marine provinces) (62)
                    (232), each characterized by a main biome type (5)
                      (biotopes)
                        : Palearctic
                          : Dinaric Mountains mixed forests (PA0418) biome type: temperate broadleaf and mixed forests
                            : Orjen, vegetation belt between 1,100 and 1,450 m, Oromediterranean zone, nemoral zone (temperate zone)
                              : Oreoherzogio-Abietetum illyricae Fuk. (Plant list)
                              • Plant: Silver fir (Abies alba)

                              Marine biomes Edit

                              Pruvot (1896) zones or "systems": [33]

                              Other marine habitat types (not covered yet by the Global 200/WWF scheme): [ citation needed ]

                              Anthropogenic biomes Edit

                              Humans have altered global patterns of biodiversity and ecosystem processes. As a result, vegetation forms predicted by conventional biome systems can no longer be observed across much of Earth's land surface as they have been replaced by crop and rangelands or cities. Anthropogenic biomes provide an alternative view of the terrestrial biosphere based on global patterns of sustained direct human interaction with ecosystems, including agriculture, human settlements, urbanization, forestry and other uses of land. Anthropogenic biomes offer a way to recognize the irreversible coupling of human and ecological systems at global scales and manage Earth's biosphere and anthropogenic biomes.

                              Major anthropogenic biomes:

                              Microbial biomes Edit

                              Endolithic biomes Edit

                              The endolithic biome, consisting entirely of microscopic life in rock pores and cracks, kilometers beneath the surface, has only recently been discovered, and does not fit well into most classification schemes. [36]


                              Watch the video: Study Jams - Biomes (June 2022).