Chapter 5
BIOME
What is a biome?
A major regional type of ecosystem (biogeographical region) characterized by distinctive climate
and soil conditions and a distinctive biological community adapted to those conditions.
Temperature and precipitation are major determinants in biome distribution.
Mountains influence the biological community of a region.
Biological productivity varies greatly from one biome to another.
TROPICAL RAINFOREST
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Precipitation: above 200 cm (440 in), evenly distributed.
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Temperature: 22 to 320C the year round.
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They occur within the equatorial zone. Very little temperature oscillation and high humidity
are characteristic, a very stable environment.
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Light intensity near the ground is very low. Day and night are about the same length.
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Diversity is high: many species represented by very few individuals.
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Lianas, climbers, stranglers and epiphytes are abundant.
See:
http://www.wildnorthwest.org/gallery.php?mphoto=9&b=0&srch_strng=epiphytes&srch=yes
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Parasitic plants. See: http://www.emp.pdx.edu/htliono/images/p8.jpg
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Large mammals are few. Many amphibians and reptiles; adaptations to arboreal life.
Source: http://www.runet.edu/~swoodwar/CLASSES/GEOG235/biomes/rainforest/rainfrst.html
TROPICAL CLOUD FOREST
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Found high in the mountains of the tropics. Mist and fog keep the vegetation wet all the time.
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Temperatures are lower than in the tropical rainforest.
See:
http://www.wildnorthwest.org/gallery.php?mphoto=23&b=0&srch_strng=tropical%20cloud%20fo
rest&srch=yes
http://www.wildnorthwest.org/gallery.php?mphoto=433&b=0&srch_strng=tropical%20cloud%20f
orest&srch=yes
TROPICAL SEASONAL FOREST
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Average temperature is similar to that in the rainforest.
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Precipitation is unevenly distributed with dry and rainy seasons. The dry season may be up
to six months.
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Vegetation with a large proportion of semideciduous trees during the dry season.
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Vegetation is shorter in stature and simpler in complexity.
See: http://www.radford.edu/~swoodwar/CLASSES/GEOG235/biomes/savanna/dryforst.html
GRASSLANDS: PRAIRIES AND SAVANNAS
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Precipitation: 20 to 60 cm (10 to 20 in). Rain usually occurs in late spring and early summer.
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Average temperature: all latitudes. In temperate grasslands, summer temperatures can be
well over 38° C (100 degrees Fahrenheit), while winter temperatures can be as low as -40°
C (-40 degrees Fahrenheit).
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Grasses and forbs (broad leaf herbaceous plant) are the dominant vegetation; shrubs and
trees along streams and rivers. Abundant vegetative growth protects and enriches the soil
making it among the richest farmlands in the world.
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Large herds of herbivores dominate with their associated predators and scavengers.
TEMPERATE GRASSLANDS
Temperate grasslands have rich soils.
Their communities are a mixture of grasses and herbs.
Deep roots allow these communities to survive heat, cold, drought and fire.
Source:
http://www.runet.edu/~swoodwar/CLASSES/GEOG235/biomes/tempgrass/prairie.html
http://www.ucmp.berkeley.edu/glossary/gloss5/biome/grassland.html
Interesting sites: http://www.runet.edu/~swoodwar/CLASSES/GEOG235/biomes/intro.html
Grasslands are known throughout the world by different names: prairies, pampas, steppes and
veldt.
The rise of the Rocky Mountains caused a rain shadow that favored the development of
grassland on their eastern side.
The soil is very rich and most grasslands have been converted to agriculture, mostly grains:
corn, wheat, barley, and other cereals.
Overgrazing is destroying the grasslands in many parts of the world including the American
west.
DESERT
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Low precipitation and high evaporation. The potential to lose water by evaporation exceeds
precipitation.
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Precipitation: 0 to 25 cm (0 to 10 in). Infrequent and unpredictable from year to year.
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Average Temperature: all latitudes.
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Vegetation made of succulents, shrubs and small trees. Some plant adaptations are: leaves
reduced to spines; thick epidermis; water-storage tissues. Vegetation varies with the amount
of annual rainfall.
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Animals with behavioral, physiological and structural adaptations to conserve water, find and
store food, and lose heat.
Picture source: http://helios.bto.ed.ac.uk/bto/desbiome/biome.htm
Interesting pictures: http://helios.bto.ed.ac.uk/bto/desbiome/cacti.htm#top
http://helios.bto.ed.ac.uk/bto/desbiome/mamgall.htm#TOP
http://helios.bto.ed.ac.uk/bto/desbiome/ecologal.htm#top
Deserts are very vulnerable to disturbance: plants grow very slowly, soil recovers
slowly.
CHAPARRAL/MEDITERRANEAN/THORN SCRUB FOREST
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The chaparral is characterized by hot dry summers and cool wet winters. Temperature my
go over 40 0C. Fires are common during the dry season.
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Plants are adapted to fire, have leathery leaves, and the tallest trees are about 3 meters (10
feet). Shrubs dominate the landscape.
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It is found in the west coast of the United States, the west coast of South America, the Cape
Town area of South Africa, the western tip of Australia and the coastal areas of the
Mediterranean.
See: http://www.nceas.ucsb.edu/nceas-web/kids/biomes/chaparral.htm
TEMPERATE RAINFOREST
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Precipitation: 250 cm (100 in) often in the form of fog condensation.
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Temperatures are mild.
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Cool rainy forest often covered by fog and low clouds. Soil is rich in nutrients.
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Redwoods, hemlocks, red and incense cedars dominate the canopy. Mosses and ferns are
abundant.
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Dominant mammals are mule deer, bighorn sheep, mountain goat and elk. Wolf, fox,
coyotes, bears and wolverine are the predators.
Source: http://www.inforain.org/about_ctrf.htm
http://curriculum.calstatela.edu/courses/builders/lessons/less/biomes/rainforest/temp_rain/tempr
ain.html
BROAD-LEAVED DECIDUOUS FOREST
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Precipitation: 80 to 170 cm.
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Temperature: -7 to 26 0C.
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Warm summers and cool winters with well-distributed precipitation are characteristic.
Proximity to the ocean creates mild winters.
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A rich biome with many plant species: oak, maple, chestnut, etc. Complex stratification,
about five strata.
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Deciduous vegetation of mixed species characterizes this biome.
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Whitetail deer, black bear, wolf, fox, raccoons are the common mammals in North America.
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The dominant biome in eastern North America, most of Europe, eastern China, Japan,
central and southern Chile. It is heavily cultivated.
Source: http://www.runet.edu/~swoodwar/CLASSES/GEOG235/biomes/tbdf/tbdf.html
TAIGA OR BOREAL FOREST
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Found between 45o and 60o north latitude. The growing season is short, less than 130 days.
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Precipitation: 40 to 100 cm (18 to 50 in), mostly in the form of snow.
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Average temperature: -40 to 15 o C. Winters are long and very cold.
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Soil is acidic, thin and nutrient poor. Bogs (muskegs) occur in depressions where drainage
is poor.
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Very large numbers individuals of very few species of plants, mostly conifers, needle leaf
trees, e.g. spruce, fir, pine. Broad leaf trees are found mixed with the conifers.
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Dominant animals are the moose, caribou, whitetail deer, brown bear, wolf, fox, lynx, rabbit,
owl, hawks, warblers, etc.
Source: http://www.runet.edu/~swoodwar/CLASSES/GEOG235/biomes/taiga/taiga.html
TUNDRA
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Far northern latitudes (arctic tundra) and very high mountain latitude (alpine tundra).
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Precipitation: 5 to 25 oC.
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Temperature: -25 to 8 oC.
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Water may be abundant but is locked up in ice and snow.
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Permafrost: the frozen soil below the thawed surface. There is little drainage as a result.
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Growing season is short, 6 to 8 weeks. Winters are long and harsh. Only the upper layer of
soil thaws out in the summer, below that the permafrost remains. Ponds, lakes and bogs are
common in the summer time.
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A grassland type of vegetation: lichens, grasses, mosses, sedges and dwarf woody plants
dominate vegetation. There is little diversity of species but large number of individuals of the
same species. One stratum of vegetation.
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Large animals found in the tundra are musk ox, caribou, polar bear, wolf, fox, seals, and
abundant bird life in the summer. Many animals migrate south during the winter and return
to breed during the short summer months.
Animals of the arctic tundra have morphological (thick stocky bodies, abundant fur and
plumage) and physiological adaptations (ability to accumulate large amounts of fat)
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Alpine tundra occurs at very high altitude throughout the world where trees cannot grow.
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Alpine tundra is exposed to high ultraviolet radiation, high ground temperature during
daytime and freezing temperature at night.
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Alpine soil is usually windswept and rocky. The terrain is sloping and well drained, in
contrast with the high latitude tundra.
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Drought is a problem due to the combination of sun, slope, soil and air currents.
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Animals found in the Alpine tundra are mountain sheep, elk, pikas, marmots, and grouse –
like birds.
Source: http://www.runet.edu/~swoodwar/CLASSES/GEOG235/biomes/tundra/tundra.html
Interesting sites: http://www.ucmp.berkeley.edu/glossary/gloss5/biome/tundra.html
http://www.runet.edu/~swoodwar/CLASSES/GEOG235/biomes/tundra/tunill.html#sedge
AQUATIC ECOSYSTEMS
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Freshwater: rivers, ponds, lakes, swamps.
Saline: ocean, salt lakes.
Basic needs of organisms:
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Photosynthesis: carbon dioxide, water, light.
Respiration: oxygen, sugar.
Growth and maintenance: mineral nutrients, food
Factors that influence the availability of needed materials:
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Substances in solution: oxygen, carbon dioxide, phosphates…
Suspended matter (turbidity): silt, plankton…
Depth
Temperature
Rate of flow
Bottom characteristics: muddy, rocky, sandy.
Internal convective currents.
Connection or isolation to other aquatic ecosystems.
Deep lakes have a thermocline (mesolimnion) or a temperature transition zone that separates
an upper warm zone from a lower cold zone.
MARINE ECOSYSTEMS
Oceans cover about three fourths of the earth’s surface.
The ocean can be divided into zones. Vertical stratification occurs in the ocean and is a key
feature of the ecosystem.
Phytoplankton is usually single-celled, minute floating photosynthetic organisms that drift
throughout the surface waters of the ocean.
Phytoplankton is restricted to the photic zone of the ocean.
The composition of phytoplankton changes with time and place due to seasonal and geographic
variations in light, temperature, nutrients, and grazing by zooplankton.
Stratification
A. Pelagic region: the large body of water, the water column.
Vertical layers of the pelagic region:
1. Photic or epipelagic zone:
 From the surface down to about 200 meters.
 Sharp gradients of light, temperature and salinity.
2. Mesopelagic zone:
 200 to 1000 meter deep.
 Little light penetrates and gradual changes in temperature.
 An oxygen-minimum layer and a high concentration of nitrates and phosphates.
3. Bathypelagic zone:
 Total darkness.
 Temperature is low.
 Great pressure.
 Depending on location, depth varies between 100 – 700 m and 2000 – 4000 meters.
4. Abyssal zone: covers the broad ocean plains down to 6,000 m.
5. Hadal zone: the benthic region in the trenches between 6,000 and 10,000 m.
B. Benthic region: the bottom.
Open ocean communities usually have low productivity.
The first hydrothermal vent was discovered in 1977. They are known to exist in the Pacific and
Atlantic oceans. Most are found at an average depth of about 2,100 meters (7,000 ft) in areas of
seafloor spreading along the Mid-Ocean Ridge system— the underwater mountain chain that
snakes its way around the globe.
How do hydrothermal vents form? In some areas along the Mid-Ocean Ridge, the gigantic
plates that form the Earth’s crust are moving apart, creating cracks and crevices in the ocean
floor. Seawater seeps into these openings and is heated by the molten rock, or magma, that lies
beneath the Earth’s crust. As the water is heated, it rises and seeks a path back out into the
ocean through an opening in the seafloor.
As the vent water bursts out into the ocean, its temperature may be as high as 400°C (750°F).
Yet this water does not boil because it is under so much pressure from the tremendous weight
of the ocean above. When the pressure on a liquid is increased, its boiling point goes up.
Chimneys top some hydrothermal vents. These smokestacks are formed from dissolved metals
that precipitate out (form into particles) when the super-hot vent water meets the surrounding
deep ocean water, which is only a few degrees above freezing.
So-called “black smokers” are the hottest of the vents. They spew mostly iron and sulfide [and
copper sulfide], which combine to form iron monosulfide. This compound gives the smoker its
black color.
“White smokers” release water that is cooler than their cousins’ and often contains compounds
of barium, calcium, and silicon, [and zinc sulfide] which are white.
http://www.ocean.udel.edu/deepsea/level-2/geology/vents.html
University of Delaware, College of Marine Science.
The hydrothermal vents heat the surrounding water to 8 -16ºC. Water at this depth is about 2ºC.
Associated with these vents, new life forms have been discovered: 3 new orders and 22 new
families; 97 of the 293 species of vent animals described so far are endemic to the vent habitat.
The primary producers are chemosynthetic bacteria that oxidize the reduced sulfur compounds,
such as H2S, to release energy, which they use to form organic matter from carbon dioxide.
Chemosynthesis, process in which carbohydrates are manufactured from carbon dioxide and
water using chemical nutrients as the energy source, rather than the sunlight used for energy in
photosynthesis.
TRANSITIONAL COMMUNITIES
CORAL REEFS form in clear, warm, tropical seas. They are the accumulated skeletons of
corals and the deposits of calcareous algae. The reefs are made of calcium carbonate. Coral
lives where light penetrates and have photosynthetic algae in their tissues. About 3/4 of the
coral reefs in the world have destroyed or seriously damaged.
ESTUARIES: bays or semienclosed areas of brackish water where rivers meet the ocean. They
are usually calm, warm, and nutrient rich; they tend to have great diversity and productivity. A
great majority of marine fish and shellfish rely on estuaries to spawn and juvenile development.
BARRIER ISLANDS: are narrow, sandy islands, parallel to the coast; they are formed where
the continental shelf is shallow and nearby rivers provide sediments; they are very important in
protecting the continental shoreline, wetlands and estuaries. The narrow strip of sea between
the islands and the coast usually has low salinity.
DELTAS are formed at the river mouths when the continental shelf is shallow and the
sediments brought by the river form a broad fan-shape sediment deposit. Deltas are often
channeled by branches of the river creating extensive wetlands that are part of the larger
estuarine zone
OCEAN SHORELINES, including rocky shore, sandy beaches and offshore barrier islands, are
particularly rich communities in life forms. Barrier islands protect the coast from the surf
especially during storms. Common along the Atlantic and Gulf coasts of North America.
FRESHWATER ECOSYSTEMS
LAKES: have vertical zones; the epilimnion is the area mixed by the wind and warmed by the
sun; the hypolimnion is below, dark and cold; the thermocline is a sharp temperature boundary
that separated the epilimnion from the hypolimnion; the bottom is called the benthic zone.
Lakes are much influenced by the surrounding land that contributes nutrients and suspended
matter.
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Thermocline: sharp temperature change between surface and deep water.
Aquatic communities are affected by nutrient availability or excess, suspended matter (silt, etc.),
depth, temperature, currents, bottom characteristics, connection or isolation from other bodies
of water.
WETLANDS: ecosystems where the land is saturated or covered with standing water at least
part of the year, e.g. swamps, marshes, bogs and fens. Wetlands convert to terrestrial
communities through sedimentation and draining. They provide essential ecosystem services,
including floodwater storage and water purification.
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Swamps are wetlands with trees.
Marshes are wetlands without trees.
Bogs are saturated ground usually composed of accumulated undecayed vegetation,
and fed by precipitation.
Fens are bogs fed by ground water and have a high mineral content.
HUMAN DISTURBANCE
Humans disturbed more than the world’s terrestrial ecosystems.
Humans preempt bout 40% of the primary productivity of the biosphere either by consuming it
directly, by interfering with its production or use, or by altering the species composition or
physical processes.
Conversion of natural habitats to human uses is the largest single cause of biodiversity losses.
Humans have disturbed mostly forests, grasslands and wetlands.
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Grasslands have been converted to agriculture, e.g. wheat, corn, etc.
Temperate forests have become cities and farms.
Wetlands have been drained, filled and converted to agriculture, aquaculture and human
habitation.
Islands like Java, Madagascar and Haiti have lost over 99% of their natural cover.
The Artic tundra and Antarctica are the least degraded ecosystem but still strongly affected in
an indirect way.