Vegetation of Southeast Asia Studies of Forest Types 1963-1965

forest subtype is generally known in Thailand (Fig. 90). The
flowers are usually small but brightly colored, and the flowering
period is short. Fruits are abundant; the seeds nave a high germination
rate, and are viable for long periods. The woods vary in
density, and are often higher than average in weight, hardness,
durability and richness of color.
Dominant and characteristic trees in this forest are: Dipterocarpus
tuber'julajms, furnishing timber for house posts; and D. obtusifolius,
its large leaves in some areas utilized for thatch and temporary
walls or partitions. In drier zones, with poor soils, these
are replaced by Pentacme siamensis and Shorea obtusa. In the Korat
plateau, where the soil is mostly sandy with occasional outcrop of
basalt, Shorea obtusa and its associates grow on sterile sandstone,
whereas in basaltic soil Pentacme siamensis shows a significant increase
.
As a rule the stands of trees, generally, are so distributed
that their crowns rarely touch. Also, the foliage is sparse so that
even at the height of the wet season the sun's rays penetrate to the
ground, and much of the rain that falls soon evaporates. The ground
cover is composed of coarse grasses, including the frequent 'kha-luang'
(Imperata cylindrica), intermixed with a cycad. Of baraboos present
in some areas, tne most frequent are: the slender 'mai ruak 1 (Thyrsos-
•cachys siamensis), and the armed "phai-pha 1 (Bambusa arundinacea).
Ground-to-ground and air-to-ground visibility, as well as ground
mobility, are generally satisfactory in this forest.
(9) THORN FOREST
This forest type is rather extensively developed in Thailand,
as in the other Mekong basin countries (Figs. 96-97). It occurs in
areas with very low annual precipitation, usually 40 inches (1,000 nnu)
or less, high temperatures, and long periods of drought. It is found
in infertile, almost bare, sandy soils. The vegetation is composed
of dense clumps of small trees, shrubs, bamboos and occasionally cacti.
Many of the characteristic plants in this growth are armed with sharp
spines (Fig. 9&), whence the term Thorn forest. Such thorny plants
are frequently abundant on plains and well-drained slopes, along
trails, and in the vicinity of habitations, whereas plants without
thorns are relatively few or absent in ouch sites. One probable
reason i'or this is that buffalo or ox-drawn carts move constantly
along these trails, and it is only the armed plants that are able to
withstand or lo survive excessive browsing by cattle.
In Thailand Thorn forest is abundant in the upper Peninsula;
in the region of Banpong and Kanchanaburi, in the west; and scattered
throughout central Thailand and the Korat Plateau in the northeast.
Characteristic trees, all of which are deciduous, Ln this forest type