Geoscience Reference
In-Depth Information
house progressively shorter trees. There may be as many as five or more layers of
trees, shrubs, or other growthforms within a tropical forest. A dense cover of
woody vines, epiphytes, and parasitic and carnivorous plants are found throughout
the canopy. Lower canopy layer vegetation typically has wide leaves to capture the
limited and filtered sunlight that escapes the upper canopy. Little plant life grows
on the forest floor, as the upper layers tend to make use of most all of the sunlight
and little reaches the ground. In the Tropical Seasonal Forest, the canopy is less
complex. Because many of the trees lose their leaves during the dry season, a dense
understory often develops.
Species are abundant in the Tropical Forest Biomes; however, in many cases
their populations are small. Many species within tropical forests have restricted dis-
tribution areas. There may be as many as 100-300 different trees within 2.4 ac
(1 ha) of tropical rainforest, but few will be found in other parts of the forest. Signif-
icantly more species than genera are found in the Tropical Forests; in other words,
the species to genera ratio is high and many congeners—species in the same
genus—are found. Nonetheless, the numbers of both species and genera far exceed
the numbers in other biomes. Several congeners may be found in one part of the
forest, while a different set is found in another area. The floral composition is much
richer and more complex in the Tropical Rainforest than the Tropical Seasonal
Forest. Both are richer and more complex than other biomes.
Climate
Equal day length, constant heat and moisture, and the effects of large water bodies
surrounding most of the tropics provide the Tropical Forest Biomes with tempera-
tures that are constant throughout the year. In general, the Tropical Rainforest
Biome's average annual temperature ranges from 79
C). Daily
temperatures are more varied than annual temperatures, shifting as much as 8
-81
F (26
-27
F
(4.5
C) in some areas, depending on cloud cover and rainfall. As you leave the
equatorial zone, the average annual temperature begins to vary slightly. In the
Tropical Seasonal Forests, temperatures are highest when the sun is not directly
overhead. Seasonal temperatures range between 68
-86
F (20
-30
C). Daily tem-
peratures in the dry season remain around 82
F (28
C), while average daily tem-
peratures in the wetter season are around 78
C) due to cloud cover.
Tropical Forests need heat and abundant moisture. The presence of frost is a
limiting factor. Frost limits plant growth and can be lethal for most tropical vegeta-
tion. Frost also limits the expansion of the Tropical Forest Biomes beyond 23
F (26
N
and 23
S latitude. These low latitude climatic regions receive 100-180 in (2,500-
4,500 mm) of precipitation annually. The rain falls throughout the year with a
seasonal decrease in some areas. In the rainforest, the dry season is not truly dry.
During this time, the rain falls intermittently, with an occasional week or two
with no rain. Precipitation amounts decrease as you move away from the Equator.
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