2 
the Brazilian jungle: “the excessive diversity of the flora and its richness in flowering 
plants forbid one to ask, what is the composition of these forests” [1]. Nevertheless, the 
invincible spirit of these former botanists to study the botanical composition of the exten- 
sive forest areas in different parts of the tropical world resulted in the fact that nowa- 
days our botanical knowledge of the tropical vegetation is, if not complete, at any rate 
much bigger than a century ago. 
The position of present-day photo-interpretation can be compared with that of the 
botanical situation of forest research in the tropics a century ago. 
Interpretation results are not yet such that we can speak of a certain perfection and 
it would therefore be erroneous to believe that we cannot go any further. We are there- 
fore glad to state that during the last 4 years:some progress has been made and we hope 
that this will continue. 
Hand in hand with this development will go the improvement of the photographic 
equipment, like cameras and films and filters, combinations specially adapted to tropical 
conditions. It should be realized that the research made in this direction in the tropics is 
still rather poor and the future possibility of absolutely new visions as regards better 
application, due to better methods in aerial photography, seems justified. Present limita- 
tions in photo-interpretation can therefore be overcome by improvement of the photo- 
graphic equipment and more efficient working methods. 
An important condition for the best results in photo-interpretation work under 
tropical circumstances is always that the man on the job should be able to check his obser- 
vations obtained from the photograph with the real situation in the field. Therefore the 
ideal procedure would be that the person in question works in the same region as where 
the photographs are made. Assuming that the photographs are not out of date or that 
the situation in the field has not changed very much after the photographs have been 
made, the interpretor is able to check his interpretation while travelling through the 
region to be investigated. This gives him the opportunity to rectify his interpretation 
work and to try to intensify his terrestrial survey. 
In this connection the work of Heinsdijk in the forestry region of the Northern part 
of Surinam (South America) should be quoted [2]. After a year of terrestrial reconnais- 
sance work he was able to delineate on the photos with a certain rate of accuracy the 
following forest types. 
a) mangrove forests, 
b) swamp forests, 
c) marsh land forests, 
d) dry land forests, 
e) non-forest areas. 
During this interpretation work it proved also to be very important to study the local 
topographie features of the terrain. This information combined with the total impression 
of the erown distribution provided a certain indication of the forest type. 
Another fortunate circumstance was created by the fact that the coastal provinces 
of Surinam were photographed on a scale of 1:20.000. Therefore tree species with a 
particular appearance on the photo and which sometimes occur in groups or in special 
typical localities as for instance along flat river courses, could be spotted and identified 
on the photograph. 
As the number of species found on the photographs by this first reconnaissance work 
was rather limited and many tree species with an exploitation value were not covered, 
Heinsdijk tried to improve his interpretation work by making a more detailed terrestrial 
survey with the aid of sample strips or single sample plots in areas previously selected 
on the photographs. As distinct orientation points in the photo were few and not always 
quite reliable (as open spots in the forest, visible in the photograph are often grown over 
after a few years) the problem of re-locating the sample plots on the photographs proved 
to be sometimes rather difficult.