Geoscience Reference
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shade may be made possible by the presence of a mutualistic relationship between
the roots and mycorrhizal fungi that helps the plants absorb nutrients. Young trees
become light demanding as they reach the canopy. Tree falls and gaps stimulate
rapid plant growth. Such gaps produce clumps of trees that grow into and above
the canopy.
Dipterocarps produce an extremely valuable wood, which is in great demand
and has led to the exploitation of these forests. Their growth habit of tall branchless
trunks and the clumping of trees allow for large-scale clear-cutting practices to
extract them economically and efficiently.
The rainforests of the Asian Pacific region are relatively poor in climbing spe-
cies apart from palms and dipterocarps. However, some climbers in the dogbane,
milkweed, morning glory, legume, and squash families are present. Climbing
palms are abundant and attain their greatest diversity in Southeast Asia. Spiny rat-
tan palms are the most diverse group; as many as 30 species can coexist in the same
area. These palms climb into the forest canopy with the help of hook-like spines on
their young stems and the underside of leaves that allow them to grab onto the of-
ten-smooth bark of tropical trees. Rattan palms are in high demand for use in furni-
ture and are intensively harvested. East Malesia is relatively poor in climbing
plants other than palms and pandans.
Epiphytes are abundant throughout the Asian-Pacific rainforest except for Aus-
tralia. Palms, ferns, orchids, and even dipterocarps are dominant. Orchids are
found throughout Southeast Asian and New Guinea. Thirty-four percent of the
world's orchids are found in tropical Asia and New Guinea, but only 3 percent
occur in Australia. Species of the genus Bulbophyllum reach their peak in these rain-
forests. The flowers of these orchids are often tiny and purple in color and have a
foul smelling odor to attract their main pollinator, flies. More than 1,000 kinds of
large, showy dendrobium orchids are also found in this region. They seem to come
in every possible color and shape. Bird's nest ferns are abundant and fill a niche
similar to the bromeliads in the Neotropics. They trap dead leaves and organic mat-
ter, but they do not form water-filled reservoirs.
In East Malesia, dipterocarps are present but play a less-dominant role than in
West Malesia. Trees in the laurel, melastome, nutmeg, and mulberry families are
also found here. Many endemic species, including primitive conifers from the arau-
caria (Araucariacea) and podocarp (Podocarpaceae) families, relicts of ancient
gymnosperm forests, are found in the rainforests of New Guinea and Australia.
These conifer families show a disjunct Gondwanan distribution, meaning they
occur in widely separated regions of South America, Australia, and New Guinea.
They were probably more widespread prior to the breakup of Gondwana and the
evolution of flowering plants.
Heath Forests. Heath forests are rainforests on sandy soils within Borneo. In Bor-
neo, they are called ''kerangas,'' a local term meaning ''land where rice will not
grow.'' The soils in heath forest are infertile. Kerangas have trees and shrubs with
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