Vegetation of Southeast Asia Studies of Forest Types 1963-1965

usually 30 ft. (10 m.). r^e length varies from 120 ft. (40 m.) upwards,
depending upon the type and density of the forest, .and the
number of species encountered within the plot. In a Dipterocarp
forest, which is relatively homogeneous, the length may be only 90 ft.
(30 m.); in a Dry Evergreen forest, 120 ft. (-'-0 m.); while in an Everyrsen
Rain or Moist forest, which is more complex and with many
varied species, the length should be at least 180 ft. (60 m.).
All trees, shrubs, vines, palms, bamboos, ferns, rattans and herbaceous
plants in and around the transect site are identified botan-
Ically as far as possible, and recorded on the spot (Fig. 123). A
record is also made of useful, edible or hazardous plants. Herbarium
materials are collected from nlarvbs which cannot be identified
immediately, anu are deposited at the Thai Forest Department for
later determination t A record is also made of data relating to the
forest community - its physiognomy, structure, location, altitude,
exposure, aspect, drainage and Glope of the plot. The position of
each tree on the fcase line, in the transect, and its distance from
thf. base are determined and listed; also the height and girth of
trunks, width of crown and anr^le of branches are reported; and density
of foliage of individual tree is evaluated. These data are reproduced
in a profile diagram drawn to scale. At the same time notes
are token on the nature, amount and depth of litter. Samples of top
and sub-soils are collected, for mechanical and crx nical analysis
(Fif 1 ;. 12H), accompanied by a record of depth, color and texture of
respective samples taken from different horizons in the transect.
Another phase of the project, designed to neet military requirements,
is to determine ;ro!ii:d-tc-,;jround. and ^round-tn-air visibility.
Several methods have oeen considered. One simple system adopted,
to evaluate horizontal visibility in a sample plot, i for a man to
:stand in a selected spot, while a second man paces in a straight line
alone one of the cardinal poir.ts through the underbrush until he is
no longer visible. This is. repeated on the other cardinal points.
The extreme distance at; which the person or object is visible in
each direction is recorded to compute the average. This is taken as
the index i'or that forest community and at t ;% at particular time of day,
To evaluate ,ground-to-air visibility, or penetrability through trio
canopy, a series -of olack-rind-'.' 1 ute photot i ;rapp.s are taken at each
sample plot. The equipment used is a Kodak K