PLANT SUCCESSION. 241 



well-grown, Fagara eapensis. In this case there is little doubt 

 but that the branch was killed by white ants, as these had 

 eaten out a considerable portion of the wood of the branch. 

 A smaller branch has also been attacked, but has not yet 

 fallen and still bears a few leaves. The remainder of the 

 clump consists principally of Glerodendron glabrum. Other 

 trees present are: — Fagara eapensis, Zizyphus mucronata, 

 Ehretia hottentotica. (See Plate II, Fig. 2.) 



Clump 3. — A very small clump, one of the youngest on 

 the hillside. A young Cussonia spicata in the centre, still 

 quite healthy, and bark not yet stripped off lower portion of 

 trunk. Surrounding this are:— Ehretia hottentotica (princi- 

 pally), Glerodendron glabrum, Zizyphus mucronata. 



Clump 4. — A very open clump on somewhat broken 

 ground. A very old and large Cussonia spicata, still quite 

 healthy looking; a second quite dead, but not yet fallen (death 

 in this case could not possibly have been due to shading) ; a 

 third dead and fallen. Other trees present are: — Ehretia 

 hottentotica, Clerodendron glabrum, Gymnosporia buxifolia. 

 (See Plate III, Fig. 4.) 



Clump 5. — A small clump. The oldest tree a large Com- 

 bretum kraussii. Other trees are: — Clerodendron glabrum 

 (two or three trees), Fagara eapensis, Royena pattens. 



Clump 6. — A large clump composed principally of Acacia 

 ataxacantha. A large Cussonia spicata 1ms fallen and is com- 

 pletely overgrown by the Acacia. Another Cussonia has 

 probably been killed by white ants. Other trees present are: — ■ 

 Comhretum kraussii, Clerodendron glabrum, Zizyphus 

 mucronata. 



VIII. The Death of the Pioneer. 



One of the most striking features of the foregoing notes is the 



frequent mention of dead or injured trees of Cussonia spicata. In 



three of the six clumps described there is a dead Cussonia, and in 



another this tree has recently lost a large branch; with regard to 



the other two clumps one is still quite young, the other does not 



contain a Cussonia at all. Indeed no one visiting the hillside can 



fail to notice the number of dead Cussonias; it is difficult to find 



a clump in which one at least does not occur. At first the writer 



was inclined to regard this as simply a further stage of the ordinary 



succession within the clump, since it frequently happens that a 



pioneer is killed out by subsequent arrivals. These, unable at first 



to survive exposure to the full sunlight of the open veld, grow 



successfully in the shade of the pioneer. Once established, they 



grow more rapidly than the latter, and eventually overtop it. The 



pioneer, always an intense light demander, cannot tolerate the 



shade, and is consequently killed out. The succession in the thorn 



veld illustrates this very clearly. To quote Professor Bews (4): — 



"Very soon the species which hegan under the thorn tree 



grow up through it. At a fairly early stage it is common to find 



Celastriis or Ehretia towering ahove it. The lianes such as Vitis 



spp. Asparagus spp, sometimes spread all over the top of it. and 



the thorn tree may ultimately be killed." 



