THE PLANT SUCCESSION IN THE IHORN VELD. 



By Prof. John Willia.m Bkws, M.A., D.Sc. 



{Plates 6-9 and tivo text figures.) 



Introduction. 



Tree Steppe or Tree Veld (grass-land with scattered trees) 

 is one of the most extensive, if not the most extensive, of the 

 types of vegetation in the whole Continent of Africa. The 

 species composing it vary in different regions, dependent on 

 differences, chiefly in climate, but partly also and more locally 

 in dififerences in soil conditions. Practically all the dry river- 

 valleys on the eastern side of South Africa are filled with Tree 

 Veld, in which species of acacia are dominant. The Protea Veld 

 is more of a mountainous type, and extends through Rhodesia. 

 In Rhodesia, also, there are many other types, such as Baobab 

 Veld, with the baobab [Adansonia digitata) dominant. The 

 Bush Veld of the Transvaal is a combretaceous-leguminous type 

 with TenninaJia, Comhretum, Burkea, etc. The mopane {Copai- 

 fera mopane) is dominant in much of the Tree Veld of Angola 

 and South-Central Africa, while Baobab Veld extends right up 

 to the Congo. Practically the w^hole of SouthXentral Africa is 

 Tree Veld, interrupted only by patches of eastern forest on the 

 slopes of the mountains of the eastern side. In the tropics, the 

 great Congo forest and the belt of dense forest which extends 

 through the Cameroons, along West Africa, to I>iberia, covers a 

 very extensive area, but north of this and south of the Sahara 

 we again get Tree Steppe very similar to that occurring in South 

 and South-Central Africa. In many parts of the tropics and 

 sub-tropics, various ])alms (Hyplucne ventricosa, H. thchaica, or 

 dum ])alm, Borassus flabcUifer, etc.) are dominant in Tree Veld. 

 It will be seen, therefore, that any study of the development 

 of such a type as the Thorn Veld must have a very wide import- 

 ance. The area studied in detail was the Thorn Veld in the 

 vicinity of Pietermaritzburg, es])ecially the district around Bisley 

 and Foxhill. In the neighbourhood of a town, the influence of 

 man nuist always be reckoned with, to a more than usual extent. 

 It is now some 70 or 80 years since Pietermaritzburg was 

 founded, and at first for many years the thorn trees of the Thorn 

 Veld were the chief source of firewood, being much more acces- 

 sible than the forest trees in the Bush. This led to extensive 

 destruction of timber, and great areas were denuded of trees. 

 In the last 20 years, however, wattle cultivation on an extensive 

 scale has been undertaken to the north of the town. After the 

 bark of the wattle tree is stripped, the wood is sold largely as 

 firewood, and this supply has taken the place of the thorn-trees. 

 The Thorn Veld, therefore, is again extending, and that fairly 



