82 



DENUDATION. 



The rainfall in the Malay Peninsula is very heavy, and in 

 exposed situations and on slopes the loss of soil in a heavy shower is 

 very large as has been already stated. Where the rain runs over 

 these slopes, in a very few minutes it is seen to be quite opaque from 

 the soil washed off. With this soil goes all exposed humus, decayed 

 leaves and sticks. The rain, however, does not run off equally over 

 the ground, it soon runs in channels formed first by some inequali- 

 ties in the ground and then by deepening these. Between these the 

 ground of the ordinary yellow clay, become covered with a thin crust 

 of an alga. In dry open spots in the Botanic Gardens, I find this 

 to be af a dark red colour, and it appears to be gelatinous alga allied 

 to Nostic. In damp shady spots the alga is green. 



There are probably several species which form these thin crusts. 

 These prevent denudation to a large extent, the water simply running 

 over the alga, and- not touching the soil. If left, mosses and hepatics 

 grow over the alga and eventually higher forms of plants. Should 

 the water rush be too strong in any part of the ground, denudation 

 takes place at a very rapid rate. When grass grows over the stiff clay 

 soil it prevents denudation to a very much larger extent, and in a 

 few years produces a layer of humus which fact itself shows that 

 denudation has been stopped, the roots also break up the stiff clay 

 soil for some depth, and render it possible for other roots to penetrate. 



In examining, the rubber plantations in the Botanic Garden a 

 very strong contrast is to be noticed where a path through the trees has 

 been opened and kept free of grass. The ground is covered with roots 

 of Para rubber trees, the tops of which are an inch and a half or more 

 above the soil. Examining the ground on the other side of the tree, 

 which is not weeded I find the corresponding roots as much or more 

 below ground, so that the opened path (not opened many years, and 

 well shaded so that the rainfall is broken up by the foliage above and 

 does not fall so heavily on the ground) has lost four or five inches of 

 soil since it was opened. 



In the case of anothor lot of trees seen in Perak, where the 

 ground was bare, sloping and of stiff clay, roots as thick as the wrist 

 were completely exposed and dead, the ends being gone. These 

 roots must have been originally some distance under ground. The 

 roots of the Para rubber lie usually very high, but this doubtless 

 depends to a large extent on the depth of the water, in the soil. In 

 the damper parts of the Botanic Gardens the rootlets of the Para 

 rubber come quite to tbe surface wherever there are any decayed 

 leaves and even sometimes rise up between scraps of detached bark 

 on the trunk of the tree itself. Dead wood, old stumps are quickly 

 invested and permeated by them. This I think shows that Para 

 rubber demands good humus and is ready to utilize all it can find. 



