Vegetation of Southeast Asia Studies of Forest Types 1963-1965

depth of 3 feet (l m.) or more in many places.
Highlands; The Annam Mountains extend on a more or less north
and south axis for about 625 miles (1,000 kms.). The crest of these
mountains forms a broken series of perUcs varying in altitude from
5,0't ft. (1,5'*2 m.) to the highest peak, Ngoc-Linh, 8,251 ft.
(2,509 rn«) above sea-level, and is located about 60 miles (96 kms.)
from the coast.
The plateau of Darlac, a basin with an irregular surrace and
ranging from 656 to I,o40 ft. (200-500 m.) above sea-level, occupies
an area of about 5, J »05 square miles, located in the northwest between
the mountains and the boundary separating South Vietnam from Cambodia.
The vegetation on this highland is composed mainly of broadleaf trees
and bamboo, which appear to thrive on dark red soils of lateritJe
origin.
Between the plateau of Darlac anrl the lower foothills there is a
mountainous area, the Plateaux Montagnards du Sud, with an area of
about 3;800 square miles, and varying in altitude between 3>280 a nd
6,560 ft. (1,000-2,000 m.). In the cool climate, prevailing at these
altitudes, two species of pine, (the 2-needied Pinup merkusii and. the
3-needled P. khasya) constitue the dominant forest growth^ mixed with
broadleaf trees and ban^oos in trie lower valleys and ravines (Fig. 11).
Dalat, the principal city, is located near the center of this area.
The basic formation of these mountains appears to be principally
granite and basaltic upheaval. Many rivers and streams have their
sources in the mountain areas, but none have the magnitude of the
Mekong. Among the principal rivers that have their source In the
Annam Mountains and flow west into Cambodia are Se Bang Khan, Nam
Lieau and Krong Pok. Other smaller streams, originating in these
mountains, flow eastward into the South China Sea, such as Da Nhim,
Bai Gun,' Son, Song Kon and Song Ben Hai, the latter separating South
Vietnam -.Yo:n Cornraunist-controlled North Vietnam, at the 17th Parallel.
As in the case of most rivers with mountain sources there are
many rapids and waterfalls cutting through rocky gorges. Extensive
areas in most of the watersheds hf.ve been denuded of forest growth by
shifting cultivation. Many of the mountain-born streams carry relatively
clear wai;er, except during periods of flash floods.
In the mountainous areas of the interior, distant from the highway,
there are large extensions of open Dipterocarp forests, composed
of trees with short boles, and mixed with stretches of savannas.
These open forest, which French ecologistsclassified as 'forSts claires,'
grow in soils with hard pan. Other sites formerly cleared for cultivation,
and later abandoned, are densely populated by encroaching brush vegetation.
As in Thailand, Laos and Cambodia, shifting cultivation has long been
widely practiced by the hill tribes. This primitive method is difficult.
to control in the more remote or inaccessible areas. For this reason
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