Tropical Rain Forest
Tropical rain forests are home to more species than all other land biomes combined. The leafy
tops of tall trees- extending up to 70 meters above the forest floor – form a dense covering
called a canopy. In the shade below the canopy a second layer of shorter trees and vines forms
an understory. Organic matter that falls to the forest floor quickly decomposes and the
nutrients are recycled.
An average of 50 to 260 inches (125 to 660 cm.) of rain falls yearly.
Rain forests belong to the tropical wet climate group. The temperature in a rain forest rarely
gets higher than 93 °F (34 °C) or drops below 68 °F (20 °C); average humidity is between 77
and 88%; rainfall is often more than 100 inches a year. There is usually a brief season of less
rain. In monsoonal areas, there is a real dry season. Almost all rain forests lie near the equator.
Rainforests now cover less than 6% of Earth's land surface. Scientists estimate that more than
half of all the world's plant and animal species live in tropical rain forests. Tropical rainforests
produce 40% of Earth's oxygen.
A tropical rain forest has more kinds of trees than any other area in the world. Scientists have
counted about 100 to 300 species in one 2 1/2-acre (1-hectare) area in South America. Seventy
percent of the plants in the rainforest are trees.
About 1/4 of all the medicines we use come from rainforest plants.
Abiotic Factors: Hot and wet year-round, thin nutrient-poor soils
Geographic Distribution: Central America in the Amazon River basin. Africa - Zaire basin, with
a small area in West Africa; also eastern Madagascar. Indo-Malaysia - west coast of India,
Assam, Southeast Asia, New Guinea and Queensland, Australia.
Desert
All deserts are dry – in fact, a desert biome is defined as having annual precipitation of less than
25 centimeters. Beyond that, deserts vary greatly, depending on elevation and latitude. Many
undergo extreme temperature changes during the course of a day, alternating between hot and
cold. The organisms in this biome can tolerate the extreme conditions.
Abiotic Factors: low precipitation, variable temperatures; soils rich in minerals but poor in
organic material
Geographic Distribution: Africa, Asia, the Middle East, United States, Mexico, South America,
and Australia
Temperate Woodland & Shrubland (Chaparral)
This biome is characterized by a semiarid (kind of dry) climate and a mix of shrub communities
and open woodlands. In the open woodlands, large areas of grasses and wild-flowers such as
poppies are interspersed with oak trees. Communities that are dominated by shrubs are also
known as chaparral. The growth of dense, low plants that contain flammable oils makes fires a
constant threat.
Abiotic Factors: hot dry summers; cool, moist winters; thin, nutrient-poor soils; periodic fires
Geographic Distribution: western coasts of North & South America, areas around the
Mediterranean Sea, South Africa, and Australia
Temperate Grassland
Characterized by a rich mix of grasses and under laid by some of the worlds’ most fertile soils,
temperate grasslands – such as plains and prairies – once covered vast areas of the Midwestern
United States. Since the development of the steel plow, however, most have been converted to
agricultural fields. Periodic fires and heavy grazing by large herbivores maintain the
characteristic plant community.
Abiotic Factors: warm to hot summers; cold winters; moderate seasonal precipitation; fertile
soils; occasional fires
Geographic Distribution: central Asia, North America, Australia, central Europe, and upland
plateaus of South America
Tropical Savanna
Receiving more seasonal rainfall than deserts but less than tropical dry forests, tropical
savannas, or grasslands, are characterized by a cover of grasses. A savanna is a rolling grassland
scattered with shrubs and isolated trees, which can be found between a tropical rainforest and
desert biome. Not enough rain falls on a savanna to support forests. Savannas are also known as
tropical grasslands. They are found in a wide band on either side of the equator on the edges of
tropical rainforests.
Savannas have warm temperature year round. There are actually two very different seasons in
a savanna; a very long dry season (winter), and a very wet season (summer). In the dry season
only an average of about 4 inches of rain falls. Between December and February no rain will fall
at all. Oddly enough, it is actually a little cooler during this dry season. But don't expect sweater
weather; it is still around 70° F.
Abiotic Factors: warm temperatures; seasonal rainfall; compact soil; frequent fires set by
lightning
Geographic Distribution: large parts of eastern Africa, southern Brazil, northern Australia
Temperate Deciduous Forest
The average annual temperature in a deciduous forest is 50° F. The average rainfall is 30 to 60
inches a year.
In deciduous forests there are five different zones. The first zone is the Tree Stratum zone. The
Tree Stratum zone has height ranges between 60 feet and 100 feet. The small tree and sapling
zone is the second zone. This zone has young and short trees. The third zone is called the shrub
zone. The Herb zone is the fourth zone. It contains short plants such as herbal plants. The final
zone is the Ground zone. It contains lichen, club mosses, and true mosses.
The deciduous forest has four distinct seasons, spring, summer, autumn, and winter. In the
autumn the leaves change color. During the winter months the trees lose their leaves.
The animals adapt to the climate by hibernating in the winter and living off the land in the other
three seasons. The animals have adapted to the land by trying the plants in the forest to see if
they are good to eat for a good supply of food. Also the trees provide shelter for them. Animal
use the trees for food and a water sources. Most of the animals are camouflaged to look like the
ground.
The plants have adapted to the forests by leaning toward the sun. Soaking up the nutrients in
the ground is also a way of adaptation.
Abiotic Factors: cold to moderate winters; warm summers; year-round precipitation; fertile
soils
Geographic Distribution: eastern United States; southeastern Canada; most of Europe; and
parts of Japan, China, and Australia
Northwestern Coniferous Forest
Mild, moist air from the Pacific Ocean provides abundant rainfall to this biome. The forest is
made up of a variety of conifers from giant redwoods, along the coast of northern California to
spruce, fir, and hemlock further north. Moss often covers tree trunks and the forest floor.
Flowering trees and shrubs such as dogwood and rhododendron are abundant. Because of its
lush vegetation, the northwestern coniferous forest is sometimes called a “temperate rain
forest”.
Abiotic Factors: mild temperatures; abundant precipitation during fall, winter, and spring,
relatively cool, dry summer, rocky, acidic soils
Geographic Distribution: Pacific coast of northwestern U.S and Canada, from northern
California to Alaska Boreal Forest
Boreal Forest/Taiga
Along the northern edge of the temperate zone are dense, evergreen forests of coniferous trees.
These biomes are called boreal forest, or taiga. Winters are bitterly cold, but summers are mild
and long enough to allow the ground to thaw. The word boreal comes from the Greek word for
“north” reflecting the fact that boreal forests occur mostly in the Northern Hemisphere.
Abiotic Factors: long, cold winters; short, mild summers; moderate precipitation; high
humidity; acidic, nutrient-poor soils
Geographic Distribution: North America, Asia, and northern Europe
Tundra
The tundra is characterized by permafrost, a layer of permanently frozen subsoil. During the
short, cool summer, the ground thaws to a depth of a few centimeters and becomes soggy and
wet. In winter, the topsoil freezes again. This cycle of thawing and freezing, which rips and
crushes plant roots, is one reason that tundra plants are small and stunted. Cold temperatures,
high winds; the short growing season, and humus-poor (humus is the organic component of
soil, formed by the decomposition of leaves and other plant material by soil microorganisms)
soils also limit plant height. The tundra is a bleak and treeless place. It is cold through all
months of the year. Summer is a brief period of milder climates when the sun shines almost 24
hours a day. It has been called "the land of the midnight sun". But even the sun can't warm the
tundra much. The short summer lasts only 6 to 10 weeks. It never gets any warmer than 45 or
50° F. During the long winter months the sun barely rises and it is dark for most of the day.
Abiotic Factors: strong winds; low precipitation; short and soggy summers; long, cold, and
dark winters; poorly developed soils; permafrost
Geographic Distribution: northern North America, Asia, and Europe
Estuary
An estuary is an area where a freshwater river or stream meets the ocean. In estuaries, because
the salty ocean mixes with a freshwater river, the salinity (salt-content) of an estuary is lower
than that of sea water, and is called brackish. An estuary typically forms at the tidal mouth of a
river, and receives sediment or silt carried in from terrestrial runoff. Types of estuaries include
bays and sounds. Large estuaries, like Chesapeake Bay and Puget Sound, may have many
rivers flowing into them and have complex shapes. Estuaries are environments whose salinity
and water level vary, depending on the freshwater input and the nearby ocean water.
Estuaries are often associated with high rates of biological productivity. They are among the
most productive ecosystems in the world and are home to unique plant and animal
communities. Many animal species rely on estuaries for food and as places to nest and breed. An
estuary has very little wave action, so it provides a calm refuge from the open sea.
Geographic Distribution: found throughout the world in coastal environments