Vegetation of Southeast Asia Studies of Forest Types 1963-1965

The general surface is gently undulating with scattered low
hills and shallow lakes. Large areas are flooded during the wet
season, but during the dry season the region suffers severely for
lack of water. The soils for the most part are thin and poor in
vegetation (Figs. 126, 12).
Two rivers, the Mun and,the Cliee, have thoir sources on the
western flank and flow parallel across the tableland. They join
near Ubon, close to the border of southern Laos, and then fall into
the Mekong. A great portion of the area is covered with Deciduous
Dipterocarp forest, forming an important source of timber for railroad
ties and firewood.
The northern and western borders of the plateau range from ^50
to 600 feet (137-183 m.) above sea level. At the city of Ubon the
altitude is reported to be about 150 feet ( J *6 m.). The many flattopped
peaks in the Dong Phraya Yen mountains rise to altitudes of
about £,500 to ^,000 feet (760-1,220 m.), while the Dong Rek escarpment
is generally about 1,500 feet (^5't ra.), and in places rises
to 2,200 feet (670 m.). From this scarp the land falls sharply toward
the Cambodian plain, but northward the slope is gradual to the
Mu-i River.
At the northeastern edge of the plateau there is a belt 30 to
iiO miles (50-96 kms.) wide which drains into the Mekong river. In
this strip the largest fresh-water lake in Thailand, Hong Han, is
located on the outsKirte of Sakhon Nakhon (Fig. 66). This lake,
with an area of about 64.3 square miles (lo square kilometers),
empties into the Mekong by way of the Nam Kam river. The belt is
also drained oy numerous other streams tributary to the Mekong.
CljjTiate: The savanna type climate of this region is siir.iJa^
in temperature and rainfall'to that of northern Thailand. Since
this region is a plateau, relief has less effect on t,ne climate than
it has in northern Thailand. The rainy season coincides with the
southwest monsoon, which becomes more vigorous and brings torrential
rainfall, especially when typhoons from the South China Sea pass
over the region, usually during June through September. The recorded
monthly extremes 01 rainfall in this region range from 0.2 inches
(5.3 :nm.) in January to 9«7 inches (2'ih mm.) in toy. The highest
temperature of record is 109° F. ('J3.0°C.) in April aau the lowest
is 'tl°F. (5«1°C.) in January. The dally range of temperature :nay
also be more extreme than elsewhere in Thailand. The distribution
of seasons is about the same as in northern Thailand.
('•) Southeastern Region
General features; The Chantaburi area, in the southeast, is
separated from the Korat plateau, on the north, by the valley of the
Ban Pakong river. On the west it is flanked, by the Chao Phraya plain;