[COMMISSION X B3 
| Aplendix to the INT. ARCHIV ES OF 
PHOTOGRAMMETRY, Vol. Xil4, 1956 
  
  
Recent Development in Photo-Interpretation of Tropical Forests 
by D. A. BOON, Lecturer in Forestry, I.T.C., Delft. 
When comparing the recent development in photo-interpretation of tropical forests 
with the results obtained by using the same procedure in temperate regions like European 
or North-American countries, it can be ascertained that the progress made in the tropics 
is less than the rate of development in the regions with higher latitudes. 
The reason for this delay cannot be attributed to the inability of the experts working 
in the tropies as they are always highly qualified men who did not hesitate to penetrate 
these extensive jungles and who, at the cost of many difficulties, tried to obtain the 
results they wanted. 
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Compared with similar techniques in the more advanced countries the delayed devel- 
opment in photo-interpretation has to be sought in other reasons, such as the lack of 
transport possibilities, the very heterogeneous composition of most parts of the forests 
and the photographie material to be used. 
As tropical forest areas are mostly situated in scarcely populated regions the only 
communication possibilities are navigable rivers as there are no roads. Therefore the 
surveyor is usually obliged to travel on foot, cutting his path through a dense under- 
growth while being attacked by insects and leaches. 
What a contrast to his comrades working in more temperate regions, sitting behind 
the driving-wheel of their comfortable cars, driving along good roads and jumping out 
every time they want to check the photographs with some special local forest area! 
Another drawback for the worker in tropical forests lies in the fact that often he has 
to depend on small-scale photography, mostly at a scale of 1 : 40.000 as larger scale photo- 
graphy is usually not economic in those thinly populated regions. This does not mean 
that small-scale photographs are unsuitable for interpretation purposes, as often striking 
differences between vegetation types such as the boundaries between mangrove forests 
and swampy areas, are sometimes easier to study and to delineate on small-scale photo- 
graphs than on larger scales. 
On the other hand the study of more details such as differences of crown appearances 
between different tree species on small-scale photographs is often limited, if not absolute- 
ly impossible. Therefore, in these cases where there is a possibility to check the image on 
the photograph with the situation in the field, large-scale photography for instance 
1:20.000 or 1:10.000 is usually preferred. Thus ir those regions where the local situation 
of the forest and the general appearance of the crown cover gives the impression that 
forest exploitation should be possible, it may be worth while to plan a supplementary 
aerial cover of this limited region on a larger scale. But in most cases the forester has to 
work with the photographic material at his disposal and must try to make the best of it. 
The last if not the least trouble of photo-interpretation of tropical regions is caused 
by the great variety in composition of species of the tropical forests compared with forest 
types situated at more northern or southern latitudes. It is an almost common fact that 
the number of species of trees with timber dimensions within a limited area of abt. 1 h.a 
(—2,5 acres) of a tropical rain forest is often more than 50. Compared with our temperate 
regions, where the number of tree species in a forest of natural composition in the same 
area is seldom more than 10, it is easy to realize that photo-interpretation in the tropics 
constitutes a difficult enterprise. 
It seemed reasonable to compare the present situation of photo-interpretation of 
tropical forests with the first endeavours, made about one century ago by botanists to 
obtain a better knowledge of the botanical composition of these very heterogeneous forests. 
For these scientists the task to study the botanical composition of the forests on the 
ground appeared a first to be rather hopeless and in this connection it may perhaps be 
interesting to quote the German botanist von Humboldt after his first confrontation with