200 WEST AFRICAN FORESTS AND FORESTRY 
The Goriba or Dum Palm, Hyphane Thebaica, is predominant, 
accompanied also by the Giginya or Deleb Palm, while the Date begins 
to appear. 
Within the limits of the Soudan Zone of vegetation many different 
types of savannah may be found, besides the expected alterations in 
botanical groupings resulting from the presence of perennial moisture 
or due to elevation and rocky outcrop. Leaving the latter out of 
account, a few notes may be made of some of the varieties familiar to 
travellers in the Northern Provinces. 
1. Tree Savannah or Savannah Forest. 
Across a considerable area of Central Hausaland, e.g. occupying 
a large part of the Zaria plateau west of the Bauchi Highlands, 
the country, where not cleared for farming, is covered with an open 
deciduous forest of fair height. This is a fairly closely wooded type, 
and although it contains few truly evergreen elements apart from 
those lining the streams, there is, perhaps owing to differing vegeta- 
tive periods for different species and to the double flowering season 
noted for many trees in West Africa, practically always a fair 
amount of foliage present. A proportion of the trees have well 
developed stems and fairly high crowns, with a leafy canopy which 
filters but never excludes direct sunlight, and the average height of 
the larger trees is from 30 to 40 feet. In the best developed 
portions of such forest the grasses do not predominate, but frequent 
clearings or patches of stony outcrop lead to the open conditions 
in which hardy perennial grasses take root, and annual burning 
results in the encroachment and multiplication of areas of the 
lower bush savannah referred to below. 
This variety of forest is typically seen in Zaria province, e.g. 
between the village of Ruka and the Koriga stream, near which point 
a sudden drop in elevation occurs, and is familiar in parts of South 
Sokoto, Kontagora and Nassarawa, etc. Lophira alata has its chief 
habitat here, but perhaps the prevailing and most characteristic tree 
is one called Doka, which has been identified as Isoberlinia doka, 
Craib, et Stapf. It has broad, shining leaves, and large, flat 5-6 seeded 
pods which dehisce with curling valves. It seeds abundantly, and young 
seedlings spring up quickly in the forest or by wayside clearings, etc. 
Along with it will be found its congener, the Fara doka, Isoberlinia 
Dailzielii, Craib, et Stapf., less abundant, and differing as to its more 
obvious features in having leaves not shining, a paler grey bark and a 
general slight degree of pubescence of all parts. Both species exude 
a coarse red resin, which does not appear to be of value. 
Most of the arborescent species mentioned in the list of the average 
association detailed above are to be found, sometimes harbouring 
