Vegetation of Southeast Asia Studies of Forest Types 1963-1965

Dark tropical clay soils occur chiefly in the Bangkok plain and
In the southern part of the Kra Peninsula. These are acid clays,
developed mainly frora alluvium. They are difficult to work because
they are plastic and sticky when wet and harden when dry. These
soils are productive. Yields could be increased, however, by fertilizing
and skillful management. The soils are used intensively for
wetland rice. In the Bangkok area they are planted for vegetables, ornamental
plants ind orchards. Kast of Lopburi these soils are
associated with -j-avy clay soils developed from igneous rocks. These
soils are very acid and extremely infertile,, Additional associated
soils, entirely unsuited for agricolture, are saline clays and permanently
wet soils, such as in mangrove swamps along sections of the
coast.
Alluvial soils occur throughout Thailand, but are most extensive
in the northern inter-mountain valleyc, in the Korat plateau, upper
central valley and the Kra Peninsula. These soils range in texture
from loam to eandy clay, in color from reddish brown to dark gray,
and with poor to good drainage, depending upon distance from the
stream. In most intar-mountain valleys these soils are productive
and intensively cropped. Elsewhere, particularly in the northeast,
their productivity is rather low and the pattern of cultivation is
generally the growing of wetland rice intermingled with scrub and
forest. Although alluvial soils are among the more productive in
Thailand, crop yields could be improved by irrigation and application
of fertilizers.
Thai Forests
Thailai.d is essentially a forest country. Of its total estimated
area of 200,000 sq. miles (511,900 sq. tons.), approximately 60 percent,
equivalent ''• s 120,000 sq. miles, is covered with some type of
vegetation (Fig. b). With diverse climatic and topographical patterns,
tliree broad zones are outstanding for their distinctive landscapes;
the Evergreen Rain or Moist forests of the southeast and
southern Peninsula; the dry to arid Korat plateau of the northeast;
and the mountainous northern and northwestern region, covered by a
series of veretatio- types, from Dry Dipterocarp, Teak, Oak to Pine
forests. The vegetation of Thailand shows some interesting features.
For example, numerous plant elements from the eastern Himalayas and
Assam appear along the mountain ranges on the western border, extending
to Malaysia, There is a corresponding northward extension of the
flora characteristic of Malaysia into the southern part of the
Peninsula. Curiously enough many species found in the south Peninsula
also ";row in the southeastern region.
IT wo exclude that part of the Peninsula south of about
10 N, the 1'lora of Thailand is fairly homogeneous, and is characteristic
of the entire; Southeast Asia from the Bay of Bengal to the Gulf
of Tonkin. The flora ,of Thailand shows a considerable amount of