THE PLANT ECOLOGY OF THE COAST BELT OF NATAL. 453 



cut deeply into the general surface. By a recent downward 

 movement of the continent the river mouths have been 

 " drowned." The subsidence probably exceeded 150 ft. As 

 a result extensive alluvial flats have been formed at the 

 river mouths. The whole of the actual coast-line itself is 

 covered by a mantle of blown sand to a distance of from half 

 a mile to two or three miles from the shore. Close to the sea 

 the sand-dunes are covered by psammophilous bush. 



"JMiere is little variation in the climatic conditions, most parts 

 being warm and humid with a rainfall of about 40 -in., the 

 greater portion of which falls in the hot summer season. In 

 some parts there are drier conditions, with a greater range of 

 temperature and more exposure to dry, hot winds — a difference 

 reflected in the dominance of a thornveld type of vegetation. 

 Frosts are absent or rare over the whole coast-belt. 



A floristic analysis of the vegetation shows that about 86 per 

 cent, of the genera and 36 per cent, of the species are tropical. 

 The more temperate species and the species with a wider, 

 general distribution appear early in the succession ; as succes- 

 sion advances the vegetation becomes more and more tropical 

 and the species tend to have a more restricted range. 



The various plant communities are arranged in the order of 

 the plant succession. The typical distribution of the chief 

 ones near a river mouth is illustrated in text-fig. 3. The 

 actual river mouth itself is completely closed by a sand-bar 

 across which one can walk. Periodically, however, the river, 

 assisted by exceptionally high tides, cuts through such a sand- 

 bar and the lagoon behind is drained out. At all other times the 

 water has to drain through the sand-bar. A section through 

 the plan is given at the left-hand side of the text-figure. 



The plant succession and the relationship between the 

 different plant communities can best be summarised graphi- 

 cally, as is done in text-fig. 4. The climax type for most of 

 the coast-belt is bush or forest, but in some of the drier parts 

 thorny scrub is the final stage of the succession. 



