ibo THE PLANT SUCCESSION IN THE THOKN VELD. 



or thorny scrub, which is so characteristic of many river valleys 

 in Natal. There are present very much dwarfed forest species, 

 such as Ptcvroxylon utile, Elccodcndroii croceum, Scolopia 

 seyheri, Schotia latifolia, Toddalia lanceolata, Claiisena in- 

 cequalis, Xanthoxylon capense, and woody lianes {Dalhergia 

 obovata), as well as a number of succulent or semi-succulent 

 lianes, such as Sarcostemma viniinalis, Dregia floribunda, Rio- 

 cretixM sp., Capparis spp.. Secamone sp., Ceropegia sp., Cissam- 

 pclos sp., Senecio sp. It should be noted that over most of the 

 Thorn Veld the pioneer acacias remain the dominant species in 

 the climax stage. Reference to the list which follows, however, 

 will show that other species are locally dominant, and. as men- 

 tioned above, in many cases 'the pioneer thorn-tree is killed by 

 the species which follow it. Within the Thorn Veld, therefore, 

 the succession tends to be towards the mesophytic. But whether 

 the thorn scrub should be considered a more mesophytic type 

 than the grass-land which it replaces is, of course, another 

 matter. Grassland, however xerophytic it be, is not the climatic 

 type suited to the valleys, which are very hot, and have a long, 

 dry period in winter, but where there is a sufficient supply of 

 water at a certain depth — too deep for grass roots to reach it. 

 Schimper's basic distinction between grass-land and wood-land 

 climates here appears to be a ver}- sound one. As we pass from 

 the higher veld of the hills and upper plateaus to the Low Veld 

 of the valleys, we pass from a grass-land climate, which is 

 locally (on the south-eastern slopes) a mesophytic forest climate, 

 first of all, to a climatic area which produces a Low Veld type 

 of grass-land with the tufted, low-growing variety of anthistiria 

 dominant, and finally to Thorn Veld and thorny scrub, a xero- 

 phytic type adapted to withstanding long periods of drought 

 and intense heat. 



List of Thorn Veld Species. 



The following list includes the more important and charac- 

 teristic species of trees, shrubs, and lianes found in the Thorn 

 Veld and thorny scrub. The symbols denoting frequency of 

 species are those in general use : — 



d. = dominant, l.d. = locally dominant, l.s.d. ■= locally sub- 

 dominant, a = abundant, l.a. = locally abundant, f = frequent, 

 1 = local, o = occasional, r = rare, v.r. = very rare. 



Ranunculacese — 



Clematis brachiata l.a. 



Menispermaceae — 



Cissampelos burchelliana f. 



Capparideae — 



