For Sudan as a whole, Harrison and Jackson (1958)
described fi ve major ecological zones based on fl oristic
composition, rainfall and soil types.28 Th e ecological
classifi cation now most commonly used is a modifi ed
version of the classifi cation by Harrison and Jackson.
It delineates six major divisions and a number of
subdivisions. South Sudan is classifi ed as savannah
woodland (high and low rainfall), fl ood region, montane
zone, and semi-desert. Th e savannah woodland is subdivided
into low rainfall savannah and high rainfall
savannah. Low rainfall savannah occurs mainly in the
north and is only represented in the south by a small area
in the northern parts of Upper Nile State. High rainfall
savannah covers most of the country with the exception
of the fl oodplain around the Nile and the montane
region of Didinga and Imatong Mountains. High rainfall
savannah woodland is further divided into two sub-zones
– savannah woodland and savannah woodland recently
derived from rainforest.