E 
= 1905 » 
The detection and delineation of shifting cultivation in tropical rain 
forests are demonstrated by means of a collection of aerial photographs 
at different scales. Most of the examples are stereograms mounted for 
stereoscopic vision with a pocket stereoscope. To prevent a biased 
impression about the interpretability, the delineation is reduced to a 
minimm and types are indicated by numbers. Apart from a short description 
of the system of shifting cultivation this paper willnot deal with the 
controversial views of the forester and the agriculturist on this subject. 
Neither will there be & discussion on the influence of deforestation in 
hilly and mountainous terraim on erosion and runoff. 
Shifting cultivation 
Shifting cultivation consists basically of a cycle of activities including 
clearcutting a patch of forest, burning the wood and branches, planting 
one or two crops, abandening the plot and moving on to an other patch of 
forest. According to Hauck (1974) 250 million of people are fed by the 
agriculture products of shifting cultivation. 
Most of the soils of the tropical rain forest are rather poor in nutrients 
and a second crop can give a considerably lower yield than the first. A 
large amount of the nutrients is stored in the forest vegetation and made 
available in the form of ash for an agriculture crop On the abandoned 
field a secondary forest will grew consisting in the first instance of 
light demanding species and followed by more shade tolerant species if 
seeds are present. For a long period the species composition of a secondary 
forest is different from that of the virgin forest. Depending on soil 
conditions and climate and after a rather long period of time, an amount 
of nutrients is stored again in the secendary forest and the cycle may be 
repeated (Watters 1971). 
In a forest region with a sufficiently large forest area and a low population 
density the system of shifting cultivation will give, on a sustained basis, 
an agricultural yield without permanently damaging the forests. 
The pattern visible on aerial photographs will usually be: 
- a small number of agricultural and recently abandoned fields 
- à large amount of secondary forest in age classes from young to old 
- patches of virgin forest mot yet under shifting cultivation 
forest types with soils not suitable for shifting cultivation (mostly 
lower forest types) 
forest types with soils suitable for shifting cultivation but too far 
from the present settlements.