AN (ECOLOGICAL SURVEY OF THE MIDLANDS OF NATAL. 499 



Acacia mollissima is a tree of very rapid growth, and it 

 uses more water from the soil than it aids in precipitating. 

 At the same time it does lead to precipitation, and the air, 

 having lost its moisture, naturally rises, so that more moisture- 

 laden air comes in from the sea to take its place. The large 

 wattle plantations, therefore, though they do lead to a very 

 noticeable drying up of the soil, ought at the same time to 

 increase the rainfall, and have a good effect on the climate 

 generally. 



The change in the climate — its increasing aridity — doubt- 

 less brought about largely through the influence of man in 

 interfering with the natural vegetation (though of course 

 other causes may be at work), may well in turn have a direct 

 effect on the vegetation. 'J'he destruction of forest may in 

 the first instance have led to lessened rainfall, and now the 

 lessened rainfall may cause a progressive decay of forest, as 

 well as to the more xerophytic formations gaining on the 

 mesophytic. 



It is interesting therefore to note bow all these factors 

 intei'act and affect one another, as well as react on the 

 vegetation. 



The climate affects the vegetation; interference with the 

 vegetation affects the climate ; the climate affects the soil ; 

 the soil ~ affects the vegetation ; interference with the vegeta- 

 tion affects the soil ; and the more one studies plant oecology 

 the more one is convinced that man is the disturbing factor 

 affecting them all. 



11. THE PLANT FORMATIONS AND ASSOCIATIONS. 



At first it seemed possible to adopt a strictly regional 

 system of classification, dividing the area into a high veld 

 region and a low veld region. In the grassland there is a 

 very distinct difference between the two regions, and in the 

 close bush type of the high veld region and the isolated 

 thorn tree type of the low veld region the difference is even 

 o'reater. 



