204 WEST AFRICAN FORESTS AND FORESTRY 
nobilis, Berlinia Heudelotii, Baphia nitida, Chlorophora excelsa, Cola 
laurtfolia, Parinarium subcordatum, Kigelia Aithiopica, Uapaca Guineensis 
(here a large tree and sometimes prop-rooted), Ficus spp. Smaller 
trees and shrubs are: Spathodea campanulata, Voacanga obtusa and V. 
Africana, Morinda citrifolia, Xylopia parviflora, Zanthoxylum Sene- 
galense, Oncoba spinosa, Vangueria euonymoides, Ixora radiata, Poly- 
spherta macrostyla, Garcinia ovalifolia, Myrianthus serratus, Elais 
Guineensis and Raphia vinifera. Not all of these extend far beyond 
the Benué, but the majority of them will be found in one or other 
fringing belt far into the deciduous region, and perhaps the two which 
best represent this extension of the semi-evergreen to the savannah 
are the woody climber Alchornea cordata and the tree Irvingia Smithit. 
Ina general view, Northern Nigeria, thus lying beyond the equatorial 
belt, possesses plant features which, apart from river and stream fringes, 
range between the mixed deciduous and xerophilus habit, and in the 
dry season the prevailing character of the open savannah forests is 
a monotonous drab or grey, intersected by the dark lines of greenery 
following the streams or encircling the swamps. The climate is largely 
of the continental type, with a temperature ranging from 120° F. to 40° 
or less (exclusive of thermometer readings on the Bauchi plateau), and 
a rainfall which throughout will usually fall between 30 and 50 or 60 
inches, with diminution to 20 or even 10 inches in the most northerly 
provinces. Such a climate, with the concomitant regularity of two, 
not four, well marked seasons, the dry and the wet, is entirely that 
associated with the occurrence of savannah formations, scattered bush 
with prevailing grasses, suffrutescent herbs and small trees, much open 
grass or thinly timbered park-land, with stretches of thick woods 
which are generally not heavily grassed and never cumbered with 
impenetrable undergrowth. 
Trees which are valuable timber species in the moist southern 
forests often scarcely attain reputable dimensions in the deciduous 
zone. 
These conditions also, which are doubtless partly the result of ill- 
considered human operations, put certain definite restrictions on 
cultivated species and determine the character of the natural products 
of the wild. The staple cereal is Dawa or Sorghum, instead of maize, 
with Gero or Pennisetum typhoideum in the North. Possibly the limit 
of Guinea Corn as a staple of native cultivation is also the limit of 
the savannah forests, i.e. of the region of trees of secondary size, short 
of the region of Acacias, of Geza, Combretum altum, and of scrub, 
where Bulrush Millet is the commoner. Both species are generally 
cultivated along with beans, Vigna Sinensis. The sweet potato displaces 
the yam and cassava ; industria] cultivation is represented by cotton 
and indigo. Of forest products, the most representative are Shea nuts 
and gum arabic, rather than rubber and large timber ; and lastly, both 
