COMMISSION VII: INTERPRETATION OF 
Reserves. In general, however, it is unlikely 
that aerial photography for forest purposes 
will be economical in the High Forest Region 
of Ghana, unless exploitable species can be 
identified on photographs. 
GUATEMALA 
In 1949 a preliminary forest inventory was 
started for the Petén area, which occupies the 
Northern part of this country and which is 
predominantly flat. This inventory work was 
based on aerial photography. Photographs 
were made in 1939-40 on a 1 :40,000 scale for 
purposes and the area covered 
amounted to about 35,000 sq. km. Based on 
this photographic material a forest type map 
was made to be used for additional terrestrial 
measurements and for other observations in 
order to obtain more information on the ex- 
geologic 
ploitation of timber. The entire project was 
finished within four months, a result which 
was only possible by the use of aerial photo- 
graphs. 
Based on the experience obtained the fol- 
lowing recommendations were put forward. 
The most suitable photo-scale for similar ter- 
rain conditions is 1:40,000 to 1:30,000; for 
selected more detailed 
interpretation could be made on a 1:15,000 
scale. These tests should also be more inten- 
some areas photo- 
sively surveyed in the field to be able to com- 
field with 
sponding features on the photographs. The 
information obtained by this method could be 
used to intensify 
pare the observations the corre- 
the interpretation on the 
small-scale photographs and further to ex- 
trapolate these results on the regions which 
are covered by small-scale photography only. 
Test flights are recommended to determine 
the most suitable film-filter combinations and 
the best time of the year to make photographs 
for forestry purposes. No further develop- 
ment of techniques in the use of air photo- 
graphs has been reported recently. 
DUTCH GUIANA 
The 
yhotographed 
I | ] 
northern part of this country was 
from the air in 1947-48. 
1:40,000 and 
1:20,000 scales; large-scale photography was 
Photographs were made on 
mainly made for the coastal regions. These 
aerial photographs were used to locate the 
main vegetation types of these low lands. The 
resulting type maps were found to give an ex- 
for additional forest in- 
ventory work by making strip surveys, and 
cellent foundation 
were also very useful for the location of ex- 
traction roads. 
Subsequently the local Forest Service de- 
VEGETATION 
cided to make more intensive use of aerial 
photography, and to study particularly the 
possibility of identifying valuable species on 
aerial photographs. Special attention was 
given to the identification of ‘‘baboen” 
(Virola surinamensis), a tree species which oc- 
curs in the coastal swamps of Suriname, and 
of Triplaris surinamensis a species which 
grows mainly gregariously under the same 
conditions. 
À research project to obtain more detailed 
information on the influence of photographic 
scale, films and filter combinations, and differ- 
ent diaphragm settings seemed therefore 
worthwhile. In 1956 some test flights were 
made by K.L.M. Aerocarto Ltd. Compared 
with smaller scales 1:10,000 was found to be 
the best scale for identifying individual 
baboen trees. The effects of occasional morn- 
ing haze were eliminated by using a yellow 
filter. 
Based on the test results the Forest Service 
decided in 1956 to have all baboen forest 
areas photographed from the air. The loca- 
tion of the photostrips could be determined 
by means of the interpretation made on the 
1:20,000 photographs. In total eight different 
baboen areas with a total area of 1350 sq. km 
were photographed, on a scale of 1:10,000. 
Photographs were made with a panchromatic 
film, Gevaert Aviphot 33° and with yellow 
filter no. 2. 
The identification of the baboen trees on 
the photographs was assisted by the fact that 
dominant crown canopy in the typical baboen 
areas mainly consists of this species. Another 
indication is that the baboen trees are mostly 
slightly lighter in tone than the other species. 
Occasional mis-interpretations, however, are 
always possible. Only the baboen trees with a 
crown diameter above a fixed limit value were 
counted, and these were indicated by a white 
dot. The position of these dots was afterwards 
transferred to a 10,000 map using a Sketch- 
master. Occasional checks were made in the 
held to compare the number of trees deter- 
mined on the photographs with the actual 
number on the ground. 
Based on the total number of trees within a 
certain area, a rough estimate of the total 
timber volume was made in order to plan ex- 
ploitation. Furthermore the maps proved to 
be very valuable for locating the timber ex- 
traction canals. 
The results obtained with the test photo- 
graphs regarding Triplaris surinamensis were 
not sufficiently satisfactory to justify large- 
scale photography of this forest type. The 
negative results may be due to the gregarious 
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