PWH 



16 SYLVICULTURE IN THE TROPICS 



but leaves the soil exposed to sun, wind, and rain, and 

 thus interferes with the gradual decomposition of the 

 organic remains on the soil. Weeds are also apt to 

 spring up, which not only stifle young forest growth, 

 but are apt to interfere with the proper aeration of the 

 soil and nutrition of the forest crop. Grazing on level 

 lands causes the soil surface to be beaten down hard and 

 thus to exclude air, while on slopes it loosens the surface 

 which gets washed away. Forest fires consume the 

 organic remains, and although part of their ash is left 

 behind, the physical properties of ash are not the same 

 as those of humus, and the soil deteriorates. 



