Biomes

BIOMES
Biomes are very large regions of Earth whose distribution depends on the amount
of rainfall and the
temperature in an area. Each biome is characterized by different vegetation and
animal life. There are
many biomes, including freshwater, marine, and terrestrial biomes. In the
northern hemisphere, from the
equator to the most northerly climes, there is a trend in terrestrial biomes: from
tropical rain forest, to
desert, to grasslands, to temperate deciduous forest, to taiga, and finally to
tundra in the north. Changes
in altitude produce effects similar to changes in latitudes. On the slopes of the
Appalachian Mountains in
the east and the Rockies and coastal ranges in the west, there is a similar trend
in biomes. As elevation
increases and temperatures and humidity decrease, one passes through
temperate deciduous forest to
taiga to tundra. Here is an overview of the major biomes of the world.
Marine
■The largest biome, covering three-fourths of Earth’s surface
■The most stable biome, with temperatures that vary little because water has the
ability to absorb
lots of heat and there is such an enormous volume of water
■Provides most of Earth’s food and oxygen
■Subdivided into different regions classified by amount of sunlight they receive,
distance from
shore and water depth, and whether open water or ocean bottom
■Open oceans are nutrient-poor environments compared with land
The marine biome is the largest and most stable on Earth.

TIP
The tropical rain forest has the greatest diversity of animal species of any biome.
Tropical Rain Forest
■This biome is found near the equator with abundant rainfall, stable
temperatures, and high
humidity.
■Although these forests cover only 4 percent of Earth’s land surface, they
account for more than
20 percent of Earth’s net carbon fixation (food production).
■It has the greatest plant species diversity of any biome on Earth. It may have
as many as 50 times
the number of species of trees as does a temperate forest.
■Dominant trees are very tall with interlacing tops that form a dense canopy,
keeping the floor of
the forest dimly lit even at midday. The canopy also prevents rain from falling
directly onto the forest
floor, but leaves drip rain constantly.
■Many trees are covered with epiphytes, photosynthetic plants that grow on
other trees rather
than supporting themselves. They are not parasites but may kill the trees
inadvertently by blocking
the light.
■This biome has the most animal species diversity of any biome and includes
birds, reptiles,
mammals, and amphibians.
TIP
Deserts experience the most extreme fluctuations in temperature of any biome.
Desert
■It receives less than 10 inches of rainfall per year; not even grasses can
survive.
■A desert experiences the most extreme temperature fluctuations of any biome.
Daytime surface
temperatures can be as high as 70°C. With no moderating influence of vegetation,
heat is lost rapidly
at night. Shortly after sundown temperatures drop drastically.
■Characteristic plants are the drought-resistant cacti with shallow roots to
capture as much rain as
possible during hard and short rains that are characteristic of the desert.
■Other plants include sagebrush, creosote bush, and mesquite.
■There are many small annual plants that are stimulated to grow only after a
hard rain. They
germinate, send up shoots and flowers, and die all within a few weeks.
■Most animals are active at night or during a brief early-morning period or late
afternoon, when
the heat is not so intense. During the day, animals remain cool by burrowing
underground or hiding
in the shade.
■Cacti can expand to hold extra water and have modified leaves called spines,
which protect
against animals attacking a cactus for its water.
■As an example of how severe conditions in a desert can be, in the Sahara
desert, there are
regions of hundreds of miles across that are completely barren of any vegetation.
■Characteristic animals include rodents, kangaroo rats, snakes, lizards,
arachnids, insects, and a
few birds.
Here is a sample climate graph to analyze.

Temperate Grasslands
■Cover huge areas in both the temperate and tropical regions of the world
■Characterized by low total annual rainfall or uneven seasonal occurrence of
rainfall, making
conditions inhospitable for forests
■Principal grazing mammals include bison and pronghorn antelope in the United
States, and
wildebeest and gazelle in Africa
■Burrowing mammals, such as prairie dogs and other rodents, are common
Temperate Deciduous Forest
■Found in the northeast of North America, south of the taiga, and characterized
by trees that drop
their leaves in winter
■Includes many more plant species than does the taiga
■Shows vertical stratification of plants and animals—some species live on the
ground, some in
the low branches, and some in the treetops
■Rich soil due to decomposition of leaf litter
■Principal mammals include squirrels, deer, foxes, and bears that are dormant
or hibernate
through the cold winter
TIP
The taiga—the conifer forest—is the largest terrestrial biome.

Conifer Forest—Taiga or Boreal Forest
■Found in northern Canada and much of the world’s northern regions including
Alaska, Russia,
and northern Europe
■Dominated by conifer (evergreen) forests, like spruce and fir
■Landscape is dotted with lakes, ponds, and bogs
■Abundance of rainfall allows trees to dominate the landscape
■Has very cold winters
■Is the largest terrestrial biome
■Characterized by heavy snowfall; trees are shaped with branches directed
downward to prevent
heavy accumulations of snow from breaking their branches
■Principal large mammals include moose, black bear, lynx, elk, wolverines,
martens, and
porcupines
■Flying insects and birds are prevalent in summer
■Has greater variety in animal species than does the tundra
■Seasonal temperature ranges of more than 70°C
Tundra
■Located in the far northern parts of North America, Europe, and Asia
■Called the permafrost, permanently frozen subsoil found in the farthest point
north, including
Alaska
■Commonly referred to as the frozen desert because it gets very little rainfall,
which cannot
penetrate the frozen ground
■Has the appearance of gently rolling treeless plains with many lakes, ponds,
and bogs in
depressions
■Insects, particularly flies, are abundant
■Vast numbers of birds nest in the tundra in the summer to eat the insects and
migrate south in the
winter
■Principal mammals include reindeer, caribou, Arctic wolves, Arctic foxes, Arctic
hares,
lemmings, and polar bears
■Though the number of individual organisms in the tundra is high, the number of
species is small

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BIOMES

The marine biome is the largest and most stable on Earth.

Here is a sample climate graph to analyze.

The taiga—the conifer forest—is the largest terrestrial biome.

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