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Approximately 75% of the forests are less than 10,000 ha. and are distributed 
mainly in the agricultural zone. 
Monitoring the selected forests over a 13 year period revealed a loss 
of 9853 hectares of forest cover to agriculture and exotic plantations. 
This loss represents 16.5% of the initial forested area of 59797. Depletion 
rates have been taking place at different rates in different forests. The 
highest annual rate was 490 ha. for South Nandi forest, Kakamega forest 
had a loss of 245 ha. per year while North Nandi lost 295 ha. per year 
(Table 2, Figs. 1 # D). 
The greatest loss of indigenous forest cover occured between 1972 
and 1976. During this period South Nandi was depleted by 3,222 ha., 
Kakamega by 1,180 ha. and North Nandi by 1,630 hectares. This represent 
18%, 8%, and 14% losses respectively for the areas observed in 1972. 
The tiny forests of Ururu and Bunyala have been completely cut down and 
replaced by exotic plantations. Between 1976 and 1980, the depletion rates 
droped considerably (Table 2). A comparison between 1959 aerial photo 
measurements and 1980 estimates from Landsat imagery for the Endau forest, 
indicate a trend toward total replacement of forest cover with farmland 
within the next 35 years if the present trend continues. The Ngong hills 
have much the same problem but the causes are different. Here the 18 hec- 
tares per year depletion rate has been due to selective cutting of trees 
for wood and browsing of animals leading to the replacement of the former 
forest with bushland of low potential value (Fig. 3). At the present trend 
the remaining forest will be depleted within the next 30 years. The only 
forest which has not been affected is Marsabit where the forest cover has 
remained at 13,675 hectares over the past thirteen years. 
In comparing the result between forests in the arid and semi-arid 
areas and those in the agriculturally high potential areas indicate a 
higher depletion rate for the agricultural area. This is the result of 
different forms of depletion. Degradation processes described by Synnot 
(1979) and FAO (1981) is dominant in the arid and semi-arid areas where 
frequent fires, overgrazing and draught are the main causes of depletion. 
In he agricultural areas deforestation due to the demand for wood products 
and agricultural land of an increasing human population is the cause. In 
the arid and semi-arid areas there is a potential for the forests to revert 
to a stable state if appropriate action is taken in time. But in the 
agricultural areas it is difficult to replace the indigenous forest once 
it has been clear cut. The trend has been to replace the indigenous forest 
with a plantation or to convert it into farm land. 
It was also important to have some idea as to the accuracy of the 
results. There were three main sources of error and in each case an attempt 
was made to minimize them. Since the scale of the maps had to be changed 
at least once with a reflecting projector it was estimated that approximately 
a 1% error in scale occurred on each map. The area measurements were done 
using a planimeter and major mistakes were eliminated by measuring each 
forest area twice. A total of 400 measurements were made with some forest 
being divided into several sections due to their size. On each measurement 
there was a possible error of 10 hectares or a total of 0.3%. This was 
substantiated on test areas where measurements were done numerous times. 
The third and main error was due to imagery interpretation. A number of 
images were four years old and had to be corrected by visual mapping from 
a light aircraft. The resultant error was estimated to be 20 000 hectares 
throughout. It was also important to have dry season scenes where forest 
491 
  
  
  
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