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forests. Tree diversity is equal to or higher than the Neotropical and African rain-
forests. One study in Borneo identified 300 different trees on a 2.4 ac (1 ha) plot.
The forest structure contains several canopy layers with intertwined vines and
epiphytes (see Figure 3.16). Along with the shrub and surface layers, they create
multiple layers of habitat for the creatures of the forest. The structure of the Asian-
Pacific rainforest is slightly different from that of its counterparts. Although several
distinctive canopy levels are apparent, the emergent layer is composed of clumped
trees typically of one family and often one species. Many of the trees that make up
the canopy layers are diptocarps (family Dipterocarpaceae). From a bird's-eye
view, a distinctive pattern of groups of emergent trees rising above the canopy is
quite evident, particularly in the West Malesian forests (see Figure 3.17). Emergent
trees are very tall, typically 195-230 ft (60-70 m). Like emergent trees elsewhere,
many have buttressed trunks.
The trees below the emergents, also dominated by dipterocarps in many areas,
reach heights of 100-135 ft (30-41 m). Other trees present in the canopy are in the
fig (Moraceae), laurel (Lauraceae), sapote (Sapotaceae), mahogany (Meliaceae),
and legume (Fabaceae) families. The dipterocarp and leguminous trees prefer the
sandier soils, while the other families grow on the less-fertile lateritic soils (oxisols
and ultisols).
The plants in the understory of the Asian-Pacific rainforest include shrubs and
saplings of canopy trees that are able to survive under limited light conditions.
Palms are particularly abundant. Few plants grow on the forest floor, where herbs
and ferns are present along with seedlings of the canopy trees. Some of the
Figure 3.16 Forest structure in an Asian rainforest includes tall dipterocarp species
that tower above the canopy. (Illustration by Jeff Dixon. Adapted from Richards 1996.)
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