38 SYLVICULTURE IN THE TROPICS , T . i 



owing to the same cause, the light is also more intense 

 and evaporation is more rapid. The thin air takes up 

 the moisture quickly and gives it off also more quickly. 



Another effect of increased elevation is the corre- 

 sponding increase in the rainfall. But this only holds 

 up to a certain elevation, above w T hich it again decreases. 

 The zone of maximum rainfall varies, but near the 

 equator, as e.g. in Java and Ceylon, it is between GOO 

 and 1500 metres (ab. 2000 to 5000 ft.) at the most. 



For purposes of description it may be convenient to 

 divide the forest vegetation into distinct zones, such as 

 basal zone, montane zone, and alpine zone ; but in each 

 separate locality the subdivisions made may be more 

 numerous. These zones, although distinct in their 

 component species, gradually shade into each other ; and 

 there may be certain species which may stand a con- 

 siderable range of elevation, as e.g. Palaquium grande, 

 Garcinia echinocarpa, and Kurrimia zeylanica in 

 Ceylon, which range from near sea-level to about 1500 

 metres (5000 ft). 



It is difficult in a volume of this size to go very 

 much into details in describing the variations of forest 

 floras at various altitudes all over the Tropics ; but I 

 shall endeavour to give a general idea of the nature of 

 these changes. Before doing so, how T ever, it is necessary 

 to state that another factor of locality has a powerful 

 influence in determining the character of the flora, and 

 that is the aspect or the direction of the compass which 

 the slopes of the mountains face, as it is from certain 

 directions that the moisture-laden winds come, and it 

 is the slopes receiving their impact on which the greater 

 precipitation of moisture occurs, at any rate up to a 

 certain altitude. Thus we have already seen that in 

 Ceylon the forest on the south-westerly slopes is of a 

 very wet type, with an enormous preponderance of 

 evergreen trees and with dense undergrowth, and, up 

 to a certain elevation, masses of lianas and creepers; 

 while on the other side of the mountains the forest, as 

 soon as it gets out of the zone of moisture -laden air 



