194 



THE AGRICULTURAL NEWS. 



June 20, 1914. 



yegetation in regard to the conservation and increase 

 of rainfall — a circumstance which is not always fully 

 recognized. In America it has been found that the forest 

 area on the Atlantic slopes appreciably increases the 

 moisture content of the air currents which pass over 

 them towards the West. In this way forest land in 

 continental regions lying to windward may very pos- 

 sibly augment the rainfall over extensive plains such 

 as those existing in the central States of America. 



One more beneficial effect, mechanical in nature, 

 will be referred to before we proceed to discuss the 

 relationship of these facts and ideas to the climatic 

 changes which have taken place in South Africa. The 

 mechanical effect in question is simply the protective 

 influence which trees may be made to have in regard to 

 orchard cultivation. At the present time the retention 

 of areas in forests, or, what is generally more practicable, 

 the planting of trees as wind-breaks must now be regard- 

 ed as matters of ordinary agricultural practice. The 

 physical advantages derived from wind-belts depend 

 upon the well-known fact that breezes lower the 

 temperature of the soil through their accelerating 

 influence upon evaporation; for the same reason 

 wind-breaks check the transpiration of plants. Also 

 the mechanical effect of wind upon the habit of 

 growth of plants is too obvious along the windward 

 coast of the West Indian islands to need a statement 

 that in this respect, too, the provision of wind-belts 

 serves a useful purpose. 



Turning now to the position in South Africa, 

 we learn from an editorial discussion in the Agricid- 

 4ural Journal of the Union of South Africa (for 

 April 1914) that although the concensus of opinion 

 clearly indicates that the climatic conditions in South 

 Africa are different to-day from what they were 100 

 years ago, these changes are to a large extent not 

 permanent ones. They are mainly the result of a cycle 

 •of wet and dry seasons — small cycles perhaps within 

 larger ones of 100 years duration. But this explana- 

 tion is not alone sufficient to account for many of the 

 changes observed. The view is expressed in the 

 reference quoted that it is the destruction of natural 

 forests that have played the most important part in 

 the evolution of the arid and semi-arid regions of South 

 Africa. As well as this, the gradual disappearance of 

 large sheets of water, the natural concomitant of the 

 •destruction of the forests, has constituted a factor of no 

 mean importance. This, it is interesting to know, is 

 recognized by a great many residents in the farming 

 districts of the Cape, and several of them have suggested 

 that improvements could be effected by the formation 



of huge dams. Whatever maybe the practical difficul- 

 ties in the way of carrying out this suggestion, the 

 idea seems a sound one, for not only would a consider- 

 able amount of rainfall, which is now lost, be saved, 

 but it is very probable that with considerable sheets 

 of water presented to the atmosphere, an increased 

 precipitation would be induced. It must not be 

 imagined, however, that the buildings of dams and 

 reservoirs is the only thing necessary. Such provision 

 would be an important aid, but the principal require- 

 ment for the conservation of moisture is afforestation 

 and the immediate cessation of veld fires. 



African veld in a primitive state consists of 

 a mass and tangle of coarse grass. To satisfy 

 the requirements of colonization this overgrowth 

 has to be got <rid of and the simplest process to 

 employ is fire. This process in the management 

 of stock farms is repeated annually. The natural 

 result is that the finer grasses are killed out leaving 

 the strongest to survive. These stronger grasses grow- 

 ing in bushes, provide a condition of the surface soil 

 which is well adapted for the loss of earth and rainfall. 

 With a heavy downpour of rain after a long spell of dry 

 weather, the water rushes down the hillsides, between 

 the tufts of grass making for itself and gradually deep- 

 ening enumerable channels. The process may take 

 many years to accomplish a very obvious change of 

 a climatic kind, but it is a decided forerunner of 

 denudation and desiccation. 



It will thus be seen that there are no very deep- 

 seated causes underlying the increased aridity which 

 is observable in many parts of South Africa. Although 

 partly due to a cycle in rainfall, the lowest point in 

 which would appear during the last two or three years 

 to have been with us, the principal cause is the 

 removal of vegetative covering. This being so, it is 

 possible to seek a remedy. Afforestation, a modifica- 

 tion of the system of veld burning, the construction of 

 large sheets of water, and the planting of wind-belts 

 will all help to conserve if not increase such rainfall as 

 may be received. These remedies are not parochial ones, 

 and apply equally well to the West Indies, and the 

 Tropics in general. Locally, in these colonies pasture 

 and bush fires are no uncommon occurrence and are, for 

 the reasons brought forward in this article, to be 

 strongly deprecated. 



In concluding it may not be irrevalent to call 

 attention to the fact that a natural state of aridity can 

 be met by the selection of drought-resistant types 

 of cultivated plants. This method of approaching tha 



