Vegetation of Southeast Asia Studies of Forest Types 1963-1965

Laos. It enters Cambodia before it reaches the Mekong delta of
South Vietnam. Through North Vietnam flows trie Red""*iver, so called
from the red color of the silt carried by its waters from the mountains
of Tibet, and forms the Tonkin delta. In Thailand, the Chao
Phraya river and its tributaries drain the great central plain, to
form the Menara or Chao Phraya delta, south of Bangkok on the Gulf
of Thailand.
Although the Indochina Peninsula projects far down into the
tropical oceanic zone, the climate of Southeast Asia is influenced
to a large degree by its position as a part of the great continental
mass of Asia. This is indicated by the prevailing winds, with accompanying
changes in humidity and aridity. Proximity to the sea
and regional relief also cause variations and modifications in the
climate.
The monsoon is the dominating climatic factor. Monsoons are
essentially seasonal winds blowing from one direction during part
of the year, and from another direction during the remaining months.
Throughout the region these winds result from the interaction of
two maritime air masses - the southern tropical, moving toward the
Equator in the Southern Hemisphere, and the northern tropical, movjng
towards the Equator in the Northern Hemisphere. In brief, the
r.iorvooon is largely the result of the differential heating of land
and vrnter, producing alternating dry and rainy seasons.
Based on a series of analogies, the countries of Southeast Asia
may be considered a unit. The presence of mountain ranges, which
intercept r.oisture-laden winds, results in a wide pattern of annual
rainfall, with the dominance almost throughout of alternating rainy
southwest r.ionsoon, arid dry northern or northeastern monsoon. Except
in mountainous areao, the temperatures are fairly high throughout,
with no frost at lower elevations. The varying distribution of rainfall
during the year is highly significant, being particularly
noticeable in North Vietnam, Laos and Thailand.
Covered mostly by tropical vegetation, Southeast Asia is separated
from India and Burma by mountain ranges; from China and the
Himalayas, on the north, with their essentially temperate flora;
while the vegetation of the southern Peninsula of Thailand, with
almost year-round precipitation, closely resembles the vegetation
of sections of Malaysia. While the five countries show appreciable
diversity in the vegetation cover, the principal analogy and unifying
factor is the widespread occurrence of certain tree species,
particularly those of the wood-oil family (Dipterocarpaceae). In
addition to Malaysia, Southeast Asia is apparently the major natural
range of this lar^e and important family, represented by several
genera and numerous species.
The forests of Southeast Asia may be segregated into 2 broad
classes: Evergreen and Deciduous forests. In Thailand these may
be divided into-12 principal forest types, most or all of whi'h are