- 1908 -
It is better to prepare à type of land use map with the emphasis on
shifting cultivation and to classify the forest types according to
suitability for agriculture. Practical knewledge about shifting
cultivation systems in use and the soil types is required for making
such a map.
In forest type mapping shifting cultivation areas can be delineated
according to the following practical system:
& — Clearcut fields, including fields 1n preperation for agriculture, with
crops and recently abandoned, .
b — Secondary forest (sub-delineation into age classes).
c - Grass land with "pseudo-gallery" forest.
a = Clearcut fields
The area of clearcut fields for one family is of the order of 0.2 ha to
1.0 ha, large enough to produce crops for the family during a year. Fields
larger than 2 ha can be a sign that families are working together or that the
fields are of young secondary forest. The form ef the fields are generally
in straight lines;an exception are the circular plots of indian tribes in
the Colombian Amazon.
Depending on local custum, the fields may be separated by strips of uncut
forest or are linked together. Occasionally trees are left standing because
they are too large, or the wood is too hard or they give fruits or nuts,
specially palms are left as they produce material for roof construction and
edible fruits.
Even in the field the differentiation between abandoned field and secondary
forest is not sharply defined. In the second year fast growing trees can
grow between the cassava and banana stems. To include such fields on aerial
photographs in the clearcut class depemds on personal decisions by the
interpreter and the scale of the photograph; for a small scale (1:50,000)
the tendency is to include them in the clearcut class and for a larger
scale (1:25,000) in the class of secondary forest.
b - Secondary forest
A trained interpreter will be generally able to differentiate secondary
forest from low forest types like mangrove, swamp forest, streamlet forest
and "wet savanna" forest.
The differentiation between creeper forest and secondary forest is, even
for a well trained interpreter, a difficult task. If the terrain is flat
and drainage is not visible, the location away from the streamlet can be