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forest. If permanent agriculture or husbandery is not possible, the
situation can become even worse, shortening the fallow time of the soil
under secondary forest in order to obtain the same yield of agricultural
products as from larger fields. This may result, in à rather short time,
in an abandoned area with degenerated secondary forest, shrub forest or
even a savanna type grassland.
A system commonly used in Latin America is to use secondary forest as an
interface between natural virgin forest and grassland for animal husbandery.
Because of the short dry season and the high percentage of hardwoods the
first burning of the fallen trees and the standing stumps is only partial.
Agriculture by haphazard planting between the criss-cross layer of timber
is possible, but this prevents good animal husbandery. The natural
regeneration consists mainly of Cecropia; & quick growing light tolerant
species. After 6 to 8 years the Cecropia is cut, mainly to get enough
fuelwood for burning the decaying hardwood for à second time, Then follows
grass sowing sometimes mixed with a second crop. Whether such a system can
still be regarded as shifting cultivation is a matter of opinion. The
result is an open grassland with a pseudo-gallery forest along the
streamlets.
Detection of vegetation and forest types occurring with shifting
cultivation on aerial photographs
As shifting cultivation is a dynamic process the individual agriculture
plots are not delineated individually and secondary forest is not
classified into age classes. When the aerial photographs are not up to
date and recent forest encroachment is not yet registered, it may be
advisable to include a zone around the existing shifting cultivation
indicating a possible extension of the human influence. In forest
inventory shifting cultivation will be normally excluded for volume
assessment.
Secondary forest on aerial photographs can give the same tonal and crown
structure impression as natural low forest types. A differentiation between
these two categories is therefore not always made.
Summarizing, one can state that a forest type map, made for a timber volume
inventory, will have less information about shifting cultivation than can
be deducted from the aerial photographs. Using such a forest type map for
problems related to shifting cultivation can result in an incorrect
determination of the current or future area under shifting cultivation.