130 Report S.A.A. Advancement of Science. 



-by Dr. Marloth to measure eighty inches in two months during the 

 rainless summer on the top of Table Mountain, when collected by 

 rushes standing out of the rain-gauge, as against five inches in the 

 same period collected in an ordinary rain-gauge alongside. 



Such a precipitation, collected by the foliage and retained by 

 the humus has an immense effect on the local climate as compared 

 with what happens when the grass is all burned off annually, the 

 iiumus destroyed by fire, and the moisture-attraction completely 

 destroyed. And this contrast is the more marked when, after many 

 years of veld-burning, and that occasionally out of season, the good 

 grass disappears and there grows instead scattered tufts of weeds, 

 wire-grass, or Karroo-bush, separated by wide stretches of bare 

 surface, usually washed clear of soil or hardened almost like rock. 

 No attraction for moisture exists there ; heat is reflected by day and 

 radiated by night, and the consequence is an atmosphere rendered 

 'by increased temperature all the more fit to carry all the moisture 

 it may contain. 



Now, just as the moist forest-atmosphere has a tendency to 

 affect its immediate surroundings, so also have dry carroid conditions 

 .a tendency to spread, through the hot atmosphere being able to carry 

 its moisture further and further away, while at the same time the 

 absence of vegetation on the carroid area renders the pasture-demand 

 on that around it all the greater if the small amount of stock and 

 .game in the neighbourhood is to continue to subsist there. The 

 amount of travelling to and fro in search of water and in search 

 of food also tells considerably on what vegetation remains, and 

 tends to further denude and consolidate the intervening- surface. 



Now, throughout Africa the amount of nearly bare Karroo is 

 enormous, and its proportion to the whole area is «:n great, while 

 that of forest and even of good grass-veld is so small, that the total 

 tendency is toward an extension of Karroo and a diminution of 

 forest. 



Egypt, Arabia and Persia have been transformed in this way 

 from bush country into bare desert. So also in South Africa the 

 grazing of the Karroo, the burning of the grass-veld, and the tramping 

 of stock to and from water, have effected and are still effecting 

 changes in the veld and in the atmosphere which can only end in 

 universal desert, unless means are taken to prevent this. 



Moffat, Livingstone, Brown, and others have given warnings 

 based on what they have seen, and any farmer of many years' 

 experience in the districts adjoining the Karroo can relate how the 

 vegetation has altered within his time from a fairly good grass-veld 

 into a condition of more or less decided Karroo. This I have wit- 

 nessed personallv within the past 20 years in almost all the districts 

 of Eastern Cape Colonv, where the gradual transition in its various 

 stages has been painfuHv manifest ; while the increasing dryness has 

 rendered the forests retrogressive rather than aggressive, and this 

 effect has been accentuated bv the grass fires annually encroaching 

 into the forest margin, and occasionally breaking through and doing 

 damage inside. 



