Geoscience Reference
In-Depth Information
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Homes in the Canopy
Within the Neotropical rainforest, epiphytic
species of the pineapple family, Bromeliaceae,
are the most common and abundant (see Plate
VI). Bromeliad flowers grow from a central
spike and are typically bright red, attracting the
hummingbirds that pollinate them. Leaves of
the bromeliads often overlap, creating a cap-
ture basin at their base. This small basin traps
water and detritus and is home to a variety of
organisms, including mosquitoes, spiders,
snails, frogs, salamanders, and even crabs dur-
ing some part of their life cycles. Bromeliads
provide myriad benefits to canopy animals by
providing pollen, nectar, and fruits to birds and
mammals. They provide a source of drinking
water for monkeys and other canopy animals.
Bromeliads are Neotropical in origin and distri-
bution. Only one species within the family
occurs in tropical Africa. Some bromeliads
grow in soil, but most grow on tree branches.
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Orchids (family Orchidaceae) are commonly
epiphytes here as well as in the other tropical rain-
forest regions. Some have bulbous stems that
store water. Orchids use mycorrhizae to assist in
their growth. Fungi living within the roots of the
orchid aid in the assimilation of nutrients. In
return, the orchid provides food and a home for
the fungi. The relationship is considered mutualis-
tic; that is, it is beneficial to both organisms.
Other orchids are saprophytic and receive energy
from decaying organic material.
Root Systems of Trees
Arial roots are common among tropical trees. They
provide stability and aboveground aeration for
plants in water-soaked soils. Walking palms (
Soc-
ratea
spp.) have stilt roots that seem to shift to take
advantage of the available light (see Figure 3.4).
The roots elevate the base of the trees often as
much as a 3.2 ft (1 m) off the forest floor. These
aerial roots of the walking palm allow the tree to
shift position and ''walk away'' from hazards. As
the tree sends out new roots, slowly moving away
from its original point of germination, the lower
trunk and older roots rot away and are left behind.
The spines on the stilt roots are quite large and sharp to discourage climbing fauna
and herbivory.
Flooded Forests
The Amazon River has an extremely shallow gradient, making it unable to trans-
port all of the water that falls throughout the year. Because of this, water levels rise
as high as 24 ft (7 m) in low-lying areas. During the rainy season, the forests of the
Amazon Basin experience severe flooding. There are two types of seasonally
flooded forests: the igap
o forest grows along
the black water rivers where the water is low in nutrients. These rivers have a black
color caused by humic acid. The v
o forest and the v
arzea forest. The igap
arzea forests grow along the white water rivers
that carry fertile sediment from the Andes Mountains. The v
arzea forest has higher
species diversity than the igap
o forest. Trees in both forest types are adapted to an-
nual flooding. They have thick, protective bark. If leaves are underwater, they stop
metabolizing, but the tree does not shed its leaves. The trees continue to flower and
carry fruits above the waterline. Many plants depend on this annual flooding to dis-
perse their seeds. The rubber tree depends on fruit-eating fish to spread its seeds.
