With the onset of human activity we have two sets of forces shaping the forests. On
the one hand we have the climate, with forests expanding during wetter periods and
contracting during drier ones. On the other we have the human factor, with cultivation
and cattle herding increasing and decreasing as human populations grew in number and
then, because of droughts and diseases, fell back again.
Forest expansion at lower altitudes may have reached a maximum around 7000–5000
years ago, at which time Budongo may have been the northernmost part of the long
continuous forest already described, running from the Semliki junction with the Congo
forest in a northeasterly direction along the eastern side of the Albertine Rift. After this
time, slow drying became the dominant process of climatic change, with a particularly
dry period from 1000 to 700 years ago. This may have reduced forest cover to what are
now riverine areas, with drought-induced human migrations bringing people into close
proximity with the remnant forests at that time, such as the earthworks found in the
Bugoma Forest to the south of Budongo already referred to (Shiel 1996).
Thus the western Ugandan forests waxed and waned over the centuries, and the
wildlife within them increased during periods of forest growth and declined as the forests
retreated. These periods of growth and decline were occurring along an axis from south-
west to northeast, on the eastern side of the Rift Valley. The point of contact with the
great forest of Congo was the Semliki Forest region to the south of the Ruwenzori
mountains. This area was the entry point for forest species into Uganda during wetter
periods. Species entered at those times and survived in the newly formed forests to the
east of the Rift Valley, then as conditions grew drier or as humans cut down the forest
they died out. With wetter conditions again or with human decline due to disease,
species entered again and re-established themselves. We don’t know how often this may
have happened. But we can see the effects of all this activity and they have been quite
dramatic. Because the entry point has always been to the southwest, more species have
always been able to enter and re-enter from there and so today more species are found
in the more southerly forests than in the more northerly ones. More monkey species are
found as you travel southwest from Budongo. For example, the red colobus monkey
(Procolobus badius) and grey-cheeked mangabey monkey (Cercocebus albigena) are
found in Kibale forest but not in Bugoma or Budongo, both of which provide perfectly
acceptable habitats for them. Budongo Forest, with its four forest monkey species (blues,
redtails, black and white colobus and forest baboons) and its single common prosimian
species (pottos,Periodicticus potto), is poor in terms of numbers of primate species and
this is because it is almost at the end of the migration or recolonization line, with only
small forests such as Zoka, Mt. Kei and Otzi further north. It is understocked with
primate species. It has very high densities of monkeys: the forest is full of monkeys, but
it is species-poor. And when it comes to the prosimians, Budongo Forest has almost
none of the bushbabies (Galagospp.) found further south; it just has pottos.
This brings us to a puzzle: Budongo, at or near the end of the line, does have a goodly
population of chimpanzees. So does Bugoma, as well as the forests farther south. In other
words, whereas some monkey species and some prosimian species failed to reach
Budongo in the most recent period of forest expansion, chimpanzees did. Why? The
8 The Budongo Forest