Geoscience Reference
In-Depth Information
species within individual forested areas have found varying yet large numbers of
individual species within the areas studied. Plant species estimates range from 105
per 2.5 acres (1 ha) in Puerto Rico to as many as 900 in 2.5 acres (1 ha) in the Ecua-
dorian rainforest. Increasing rainfall is positively related to high species diversity.
A number of tree families are represented in the emergent layer. Trees in the
trumpet creeper (Bignoniaceae), Brazil nut (Lecythidaceae), and vochysia (Vochy-
siaceae) families occur in other forests but are most diverse in the Neotropical rain-
forest. Other plant families present among the canopy layers include the balsawood
(Malvaceae), kapok tree (Bombacaceae), legume (Fabaceae), and fig (Moraceae)
families, along with members of the euphorb (Euphorbiaceae), coffee (Rubiaceae),
and palm (Arecaceae) families.
Tropical trees can have bark of a variety of colors from light to dark, with or
without splotches, and in a variety of thicknesses. The wood is often hard and
dense as a protection against the wood-eating termites that are plentiful. Tree bark
is typically smooth to discourage the growth of vines on the tree. Some tree bark is
particularly distinctive, such as the chicle tree (see Figure 3.3). The bark of the chi-
cle tree is brown with gray spots, reasonably smooth, and deeply fissured. The
sticky substance that lies behind the bark is extracted by cutting small gashes into
the tree. Before the advent of a synthetic replacement, chicle was used in the mak-
ing of chewing gum. Chicle is still used in some natural chewing gums.
Neotropical rainforest trees have broad buttresses at the base of the trunk.
Leaves tend to be oval and have sharply pointed drip tips. Drip tips help facilitate
rainfall drainage off the leaf and promote transpiration. Many leaves are thick and
waxy, and remain on the tree for more than a year. Larger leaves are common
among trees of the lower canopy layers. The large leaf surface helps intercept light
in the sun-dappled lower strata of the forest. If these trees succeed in reaching the
higher canopy layers, their newer leaves are often smaller.
What lies within the canopy of the Neotropical rainforest has been investigated
only recently. Pioneering researchers, using new techniques for climbing and sur-
veying the canopy, have been able to document new species and species interac-
tions in and above the upper canopy. These researchers had to reach great heights
and endure pelting rain, strong winds, swaying trees, and other untold hazards.
They found that the canopy is rich in flowering trees, orchids, bromeliads,
vines, and other light-loving plants. Along with this flora abundance comes a diver-
sity of insects, arthropods, amphibians, birds, bats, rodents, and other mammals
that spend their entire life in the upper canopy, many of them never reaching the
forest surface. Some canopy trees have been found to contain as many as 200
orchids, with 1,500 other epiphytic plants within their entire height. One layer of
the canopy is in fact many layers of epiphytes, bromeliads, mosses, lichen, liver-
worts, and algae covering all types of structural surfaces, including trees, branches,
woody vines, and even mammals, such as sloths.
Little light penetrates beyond the canopy layers. Shrubs are adapted to low light
conditions and are common in the understory. They include members of families
