Geoscience Reference
In-Depth Information
with low fertility. Ultisols are susceptible to erosion and movement due to the clay
layer at depth.
Inceptisols and entisols cover equal amounts of land in the region. Three types
of inceptisols are significant: aquepts (gleysols), andepts (andosols), and tropepts
(cambisols). Although once forested, aquepts in tropical Asia are now devoted to
rice production. They have high soil fertility and support large human populations.
Andepts are of volcanic origin and exceptionally fertile. They are important soils in
the Philippines, Indonesia, and New Guinea. Tropepts are well-drained nonvol-
canic soils that occupy large areas of the Asian-Pacific region. They are similar to
oxisols and ultisols in that they have low fertility and are reddish in color. Tropepts
make up over half of the inceptisols found in the region.
The entisols are also divided into three groups: the fluvents (fluvisols), lithic
group (lithosols), and the psamments (arenosols and regosols). A little over one-
third of the entisols found in the Asian-Pacific rainforest are fluvents. These are
well-drained, young, alluvial soils found along river valleys and subject to flooding.
They are among the richest agricultural soils, and in Asia, they have been exten-
sively converted for rice production. Another 40 percent of the entisols in the
Asian-Pacific region are in the lithic group (lithosols). These are shallow soils on
steep slopes, near rock outcrops. Psamments are deep, sandy soils that are acidic
and low in fertility. Tropical heath forests, or kerangas, are found on psamments.
In the Asian Pacific, these soils occur on Borneo and Sumatra.
The remaining soil types are histosols and alfisols, with a fraction of spodosols,
aridisols, vertisols, and mollisols. Thirty-three percent of Asian soils are relatively
fertile in contrast to the dominance of infertile soils in the Neotropical and African
rainforests.
Vegetation
Floristically this region is called Malesia and is separated into two more or less dis-
tinctive subregions. West Malesia includes India, Southeast Asia, the Philippines,
the Malayan Archipelago, Brunei, and Indonesia including Borneo. East Malesian
includes the area east of Wallace's Line: Sulawesi, Lombok, New Guinea and
nearby tropical islands, and northeastern Australia. (The term Malesia should not
be confused with the country Malaysia.)
Forest Structure
The flora of the Asian-Pacific rainforest is rich and diverse; over half of the world's
flowering plants families are represented. About 2,400 genera and 25,000-30,000
species are known, many of which are endemic, although the degree of endemism
varies among the islands. Trees are mainly evergreen, with some semi-evergreen
trees occurring on the fringes of the rainforest where it blends into the monsoonal
