Vegetation of Southeast Asia Studies of Forest Types 1963-1965

Perhaps the most important factor in aerial photography of tropical
forests is the utilization of hue or tones to make spectrephotometric
measurements. The best results are obtained when few
trees are to be identified. In the tropics the great majority of
tree species are bread-leaved, and are more difficult to distinguish
from one another than from coniferous trees. There is also an intraspecies
variation in the hue of foliage. Owing to wide variations
between them, methods based on tonal differences of foliage through
the use of various film filter combinations are likely to be of
small importance in species identification from aerial photographs.
Difficulties involved in species identification are not reduced by
xhe fact that in the dense tropical forests not all the trees are
visible or identifiable in aerial photographs. This may be solved
et first by concentration on the dominant trees forming the canopy,
and by deducing from that other subordinate plants associated with
them.
Aerial photographs are also excellent in surface area assessment,
in survey work to indicate roads, drainage and major topographical
features.
In the final analysis, an aerial reconnaissance is less expensive,
without sacrificing accuracy, than a ground survey. It involves only
a fraction of the time spent in conducting on-the-spot study of the
saiue area by a team of forest-botanists and their assistants, who
have to be transported to and from the area, housed, fed, and ncved
around on the site. Combined aerial and ground data continue tc be the
best means to conduct ecological studies or forest surveys. Considerable
research still needs to be done to determine all the
characteristics of tropical forests.
Additional Studies in Northern Thailand: During 1955, while on
an assignment with the Royal Forest Department of Thailand, Loetsch
made an aerial inventory of the Teak forests of northern Thailand.
The most important facts determined were that teak, grows scatteringly
among other species in Mixed Deciduous forest, which has a rather low
stock per unit area, and that, communications to the mountainous
forests are generally very poor. The census started in 195'' -incl the
results for the five of the provinces, representing the heart cf the
teak-bearing area and yielding about 60 percent of teak production
in Thailand, were completed in June 1957.
Aerial photographs were taken on an average scale of 1: ; .8,OCO
for the o.rea below 3,000'ft. (1,000 m.) above sea level. Teak does
not generally occur above 3.000 ft., so that a contour line of 3>000
ft. was marked on-all the photographs of the northern provinces.
The area was thus divided into two main parts: that below 3>CCO ft.;
and the other.above 3,OCC ft. The sampling technique was aimed at
determining tne proportions of the area of the strata recognizable
on the photographs.
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