ECOLOGICAL NOTES 211 



Owing to overstocking, grass fires and footpaths, 

 numerous dongas have formed in the alluvial deposits 

 on the plateaux and in the valleys. Owing to the first 

 two causes dry gullies have formed rapidly on the moun- 

 tains, and much rock has been exposed, the alluvial soil 

 having been washed away. 



Climatic Factors. 



The annual rainfall sometimes is as much as 40 inches, 

 and sometimes falls as low as 23 inches. On the moun- 

 tains it is probably considerably greater. 



The seasons are clearly marked. The winter is cold: 

 frost and snow^ occurring. The spring is usually windy 

 and dry. The earl^^ summer (Dec. and Jan.) is often 

 dry, although thunder and hailstorms are prevalent. The 

 late summer and autumn is the rainy season, soaking 

 rains occuring then. 



The north and north-west aspects of the mountains 

 and escarpments are warm and dry, while the south and 

 south-east aspects are cool and damp. The western 

 aspects are exposed to dry warm winds, and the eastern 

 to damp cool winds. The vegetation on the damp side 

 of a mountain is very different from that on the hot dry 

 side. 



The humidity of the soil seems to be the chief factor 

 in determining the limits of the plant associations. The 

 humidity being dependent on the altitude or the aspect 

 of the land, and on the nature of the rock and soil, it is 

 convenient to classify the associations according to the 

 topographical factors. 



BiOTic Factors. 



These tend to affect adversely the natural vegetation. 



1. Man: — A considerable amount of land in the more 

 level parts of the country is cultivated. The bush in 

 the kloofs is destroyed by axe and fire. The veld was 

 regularly burned in the spring (but this practice is 

 illegal now), consequently the torrential rains in the 



