Vegetation of Southeast Asia Studies of Forest Types 1963-1965

(7) MIXED DECIDUOUS FOREST
This forest type is veil distributed throughout continental
Thailand, especially in the north and northeast (Figs. 67-69, 79).
It is among the most valuable assets of Thailand, as a source of
timbers, particularly teak. Bamboos also occur in abundance, constituting
important articles for domestic use and for trade. Some
species develop readily when, the forest is cutover, or when clearings,
are made for shifting agriculture.
Mixed Deciduous forest nay be divided into 2 subtypes:
Mixed Deciduous; and (b) Dry Mixed Deciduous forest.
(a) Moist
(a) Moist Mixed Deciduous forest: This subtype occurs in wellwatered
areas, with an annual precipitation of 50 to 80 inches
(1,270-2,030 mm.), and where the onset of the dry season is marked,
at. least, by a brief leafless period. The total amount of rainfall
is probably less important in the development of this forest suotype
than its seasonal distribution, and the length and severity of the
dry season.
This forest is fairly dense and tall, but is less luxuriant than
the Rain forest. It shows a definite tendency toward dominance by
a single family or genus. Sometimes it may be characterised by a
single or few gregarious species, as in the case of teak (Tectona
grandis),, which is dominant in certain areas. In parts of northern
Thailand, for example, teak constitutes a high proportion of the
Moist Deciduous forest, and is considered the country's most valuable
timber (Figs. 71-74). It is estimated that the Teak forests
of Thailand cover about 25,000 square miles (65,000 sq. kms.). In
addition, there are approximately 5,000 sq. miles (13,000 sq. tons.)
of Mixed Deciduous forest, as in the northeast, in which Teak trees
are absent.
(b) Dry Mixed Deciduous forest: In this subtype are grouped
forests with less than 50 inches (1,270vmm.) of annual rainfall,
mostly in the rainy season, followed by 6 or more months of dry to
very dry season. Most of the rain falls in heavy showers with quick
runoff, and therefore has less effective soil penetration. In
general, this forest is definitely less luxuriant and less complex
than the Rain forest or even the Moist Mixed Deciduous forests. It
is relatively simple in structure, with a single story, but occasionally
with two stories, and dominant tr.;es measure from 50 to 75 feet
(16-22 m.) in height. The canopy is often uneven, not dense, and in
some areas with open-spaced trees and shrubs. Many of the trees have
a straight, clean trunk of fairly large dimension; others are twisted,
with low branches and flat or umbrella-shaped crown. Both trees and
shrubs are leafless during the dry season, .although some evergreens
may be present. The leaves range in size from small, finely-pinnate
or simple digitate to lar^e and leathery. Woody vines, epiphytes
and ferns are few. Stilt roots and plank buttresses are almost
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