Geoscience Reference
In-Depth Information
many that have evolved particular adaptations to exist in this moist, hot, and often-
flooded environment.
The Amazon Basin contains a mosaic of ecosystems and vegetation types, includ-
ing rainforests, seasonal forests, deciduous forests, and flooded forests, among others.
The Amazon River and all its tributaries are the lifeline of these forests, and its his-
tory plays an important part in the development of rainforests. Earlier in history,
when the continents were joined as part of Gondwana, the Amazon River flowed
westward, perhaps as part of a larger Congo (Zaire) River system from the interior
of present-day Africa. The South American continental plate separated from the
African Plate and moved westward, crashing into the Nazca Plate. About 15 million
years ago, the Andes were formed, forced up by the collision of these tectonic plates.
The Amazon became a vast inland sea that gradually turned into a massive swamp.
About 10 million years ago, through years of constant rainfall and heat, water
worked through the sandstone and the Amazon began to flow eastward, permitting
the development of the Amazon rainforest. During a series of climatic changes and
Ice Ages, the tropical rainforests around the world expanded and contracted. Some
researchers suggest that during drier times, much of the Amazon rainforest reverted
to savanna and seasonal forest, leaving smaller isolated rainforests as refugia, areas
of isolated populations. When the Ice Ages ended, the forest spread and these refugia
joined, still maintaining some of their once-isolated divergent species. This may
explain some of the incredible diversity within the Neotropical rainforest.
The Choco is one of the last coastal rainforest left in the world. The Choco rain-
forest extends along the Pacific Coast of Panama, Colombia, and northern Ecua-
dor. It is recognized as a world hotspot for biodiversity and is home to a diverse
assemblage of plants and animals. More than 11,000 species of plants, 900 species
of birds, and at least 100 species of reptiles have been identified within the Choco
with many of them endemic. The Choco receives more rainfall than the Amazon,
totaling up to 630 in (16,000 mm) in some areas. The Choco was isolated from the
Amazon with the formation of the Andes mountains. This isolation allowed for a
rich array of unique species to evolve over time.
Climate
The climate of the Neotropical rainforest is consistently hot and humid. Tempera-
tures average around 88
F(31
C) during the day, with nighttime lows around 72
F
(22
C). Humidity is never less than 88 percent. Rain is abundant. In the Amazon
Basin, precipitation ranges from 80-120 in (2,000-3,000 mm) annually. This pre-
cipitation comes from the Trade Winds and the Intertropical Convergence Zone
(ITCZ), along with convective rainfall brought about by evapotransporation within
the forest. Annual rainfall in the Choco can reach 157-315 in (4,000-8,000 mm).
The Neotropical rainforest is of major importance in regulating global climate.
Carbon dioxide absorbed through photosynthesis acts as a sink, holding carbon
