Earth’s Major Biomes 141Average monthly precipitation in cm28323640
444824
20
16
12
8
4
0
Months12162024288
4
0Average monthly temperature in°CJFMAMJJASONDBased on data from http://www.worldclimate.com© Thomas R. Fletcher/Alamyor more in height, which are exposed to direct sunlight.
The middle story, or canopy, which reaches a height of 30
to 40 m (100 to 130 ft), forms a continuous layer of leaves
that lets in very little sunlight to support the smaller plants
in the sparse understory. Only 2 to 3 percent of the light
bathing the forest canopy reaches the forest understory.
Tropical rainforest trees support thick woody vines and
extensive communities of epiphytic plants such as ferns,
mosses, orchids, and bromeliads.
Not counting bacteria and other soil-dwelling organ-
isms, about 90 percent of tropical rainforest organisms
are adapted to live in the canopy. Rain forests shelter the
most abundant and varied insects, birds, reptiles, and
amphibians on Earth. Most rainforest mammals, such as
sloths and monkeys, are adapted to live only in the trees
and rarely climb down to the ground, although some
large, ground- dwelling mammals, including elephants,
are also found in rain forests.year-round as in tropical rain forests, but annual pre-
cipitation is lower and more seasonal.
Tropical rain forest commonly occurs in areas with
ancient, highly weathered, mineral-poor soil. Little
organic matter accumulates in such soils; because tem-
peratures are high year-round, bacteria, fungi, and
detritus-feeding ants and termites decompose organic
litter quite rapidly. Roots quickly absorb nutrient miner-
als from the decomposing material. Tropical rain forests
are found in Central and South America, Africa, and
Southeast Asia.
Of all biomes, the tropical rain forest is unexcelled
in species richness and variety (Figure 6.12). No single
species dominates this biome. The trees are typically
evergreen flowering plants. A fully developed tropical
rain forest has at least three distinct stories, or layers, of
vegetation. The topmost story, or emergent layer, con-
sists of the crowns of very tall trees, some 50 m (164 ft)
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A view of tropical rainforest vegetation in El Yunque National Forest,
Puerto Rico. Except at riverbanks, tropical rain forests have a closed
canopy that admits little light to the rainforest floor. Climate graph
shows monthly temperatures and precipitation for Belem, Brazil.
Interpreting Data
What is the average monthly precipitation during
this tropical rain forest’s wettest months? during
its driest months?