17 



occurrence, such as Triplochiton Johnsonii, or the striking proportions 

 reached by individuals such as Entandrophragma utile. The area over 

 which the Deciduous Forest is found is subjected to a lesser rainfall 

 than those parts covered by the Evergreen Forest. This, and the fact 

 that the Deciduous Forest comes directly under the desiccating influence 

 of the "Harmattan," frona which it itself protects the Evergreen Forest 

 to the south, would appear to account for its position and character 

 In the field the distinguishing factor of the Deciduous Forest, as a whole, 

 is that the closed canopy is formed by the lower trees, and that the 

 dominant trees have fully developed and almost isolated crowns. From 

 this fact, when any of the dominant trees shed their leaves a noticeable 

 gap amongst the huge crowns is very marked and hence the name 

 " Deciduous Forest " has arisen. 



The lianes as a whole are found trailing over the canopy formed 

 by the smaller trees, and when they do ascend the bigger trees they 

 are not able to bind them together as they do in the Evergreen Forest 

 owing to the distance the crowns are apart. The largest of the lianes 

 often attain a girth of one foot, and are, as a rule, Apocynaceous. 

 The lesser lianes and climbers are provided by the CombretacecB and 

 Leguminosce, of which Acacia pennata is probably the commonest. 



The arboreal species are the same as those of the Evergreen Forest, 

 but with the exception of some of the Evergreen Forest dominant 

 trees. This causes other species which are occasionally met with in 

 the Evergreen Forest to appear more commonly. An example is that 

 of the Wawa {Triplochiton Johnsoni), only occasionally seen in the 

 Evergreen Forest, but one of the commonest and most characteristic 

 trees of the Deciduous Forest. 



The Sudanese Zone. 



Comparatively no botanical or forestry survey work has so far 

 been carried out in this country on the vegetation of the Sudanese 

 Zone, and consequently it is not possible at the present stage to define 

 the limits of the subdivisions into Savannah Forest and Savannah. 

 The controlling factor over this zone, apart from its proximity to the 

 more arid conditions of the north, is the annual grass fires, which, 

 sweeping over an ever-extending area of country for many decades 

 must now be considered in the light of a natural factor. As has 

 already been stated, strips of the original closed forest are still found 

 in its southern edges along watercourses and on the south side of 

 the hill masses. Beyond that Savannah Forest and Savannah stretch 

 away to the north, the forest patches or isolated trees ever becoming 

 fewer. 



In the west all the country north of 7° 30' belongs to this Zone. 

 As one proceeds eastwards the hmits bear towards the south, but 



