IX. A, 5 Brown and Mathews: Dipterocarp Forests 458 



If the second-growth forest is widely separated from any 

 dipterocarp forest, it is not likely to become dipterocarp in 

 character. The first trees, which are very intolerant of shade, 

 gradually give way to other more tolerant species, and the com- 

 position of the forest becomes more complex. The trees are 

 still mostly small, soft-wooded species and of little or no value 

 in the production of timber. It is thus evident that little can 

 be expected from these forests until they have been planted with 

 more valuable species or until a neighboring dipterocarp forest 

 has spread to them. 



So far we have considered only land which has been cleared 

 and not cultivated. In the past, however, almost all clearing 

 has been for the purpose of cultivation. The succession of 

 vegetation naturally varies greatly with the subsequent treat- 

 ment, and results in the production of either grassland or 

 second-growth forest. 



The most primitive method of cultivation, and one which is 

 practiced even now by some of the wild tribes, is to make 

 a small clearing, or "caingin," in the midst of the forest, plant 

 it to rice or yams for a year or two, and then, as weeds grow, 

 to abandon it. These small patches are quickly covered by 

 second-growth trees which kill out the weeds. 



A more destructive system and one which has been very 

 generally practiced is the making of clearings on the edge 

 of the forest. These clearings are cultivated by very primitive 

 methods. Cogon grass {Imperata exaltata) or talahib (Saccha- 

 rum spontaneum) comes in along with various herbaceous an- 

 nual weeds, conspicuous among which are species of composites. 

 The area is burned over regularly, which results in the death of 

 practically all tree species and the spread of the grass, as the 

 large underground rhizomes of the latter are not injured by 

 fire. In a few years the grass takes possession of the area 

 and cultivation is abandoned, as it is easier to clear a new 

 patch of forest than to eradicate the grass by the primitive 

 methods of cultivation generally in use. 



It is at this point that the differences in climate probably 

 play their most important role in determining whether the 

 land shall remain permanently in grass or return to forest. 

 In regions with a pronounced dry season the dead leaves of 

 the grass become, in the dry weather, very inflammable. These 

 grass areas are burned over regularly. Tree seedlings are thus 

 killed, and the area remains permanently in grass. This shift- 

 ing system of cultivation has resulted in producing and extend- 



