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MONITORING RECENT CHANGES IN EXTENT OF NATURAL FORESTS
IN KENVA USING REMOTE SENSING TECHNIQUES
by
N. OCHANDA AND H. EPP
KENYA RANGELAND ECOLOGICAL MONITORING UNIT
MINISTRY OF ENVIRONMENT AND NATURAL RESOURCES
P.O. BOX 47146, NAIROBI, KENYA
ABSTRACT
Mapping of the existing forest cover in Kenya was carried out to
provide a complete and up to date inventory of the forest cover and to use
this data base to monitor forest cover changes. The mapping covered an
area of 1.37 million hectares with an estimated mapping error of 3.6%.
Critical forest areas with high depletion rates were observed at 4
years intervals starting from 1967. Much of the forest area was cleared
in the peak period of 1972-1976 and this trend appears to have slowed down
in the last few years.
Mapping and monitoring of the forest cover changes was done through
visual analysis of multi-date landsat satellite imagery and old aerial
photographs augmented by some digital analysis and information from the
topographic maps, overflights with light aircraft, and ground survey data.
INTRODUCTION
The conflicting land-use options within the agriculturally high
potential areas of Kenya coupled with an increasing population are making
a greater demand on the limited forest resources, causing rapid depletion
in some areas. Major portions of the indigenous forest reserves are clear-
cut after economically valuable trees are removed. The cleared areas do not
regenerate quickly into indigeneous forest but are turned into subsistance
level agriculture or exotic plantations or remain fallow (Miller 1979).
Heavy pressure is being exerted on the indigeneous forests without a full
awareness of the effects on the overall ecological stability. .
A state of knowledge of the existing forest cover which is required
for the correct appraisal of problems and determination of possible solutions
could be improved by continued monitoring of the changes in areal extent |
and the ecological status from the established base. Remote sensing
techniques have been used to some extent to establish the data base by
mapping the total forest cover (Doute et al 1981) and to monitor changes
in areal extent of the selected critical forest areas (Ochanda et al 1981).
The techniques have been applied with success in some countries
(Miller, 1979; Lorenzo et al 1979) for mapping of clear-cut or deterioriat-
ing forest areas. The limited access to sophisticated digital analysis and
the inconsistent supply of the appropriate products of landsat coupled
with the limitations of the Landsat sensors, limited the studies to mapping
and monitoring broad changes in the forest cover. Improvements in the Land-
sat sensor resolution to the level where three dimensional analysis is
possible with high resolution, could enhance monitoring of the ecological
status of the forests which is the much needed information for rational
management.
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