576 Forestry Quarterly. 



relative humidity, is less in the lowlands than in the high altitudes ; 

 consequently, the forests of the low altitudes may show a much 

 less evergreen appearance than the forests of higher altitudes of 

 the adjacent interior mountain passes. 



The monthly distribution of the rainfall should be considered, 

 because some localities in the regions of a long dry season receive 

 a greater annual rainfall than others in the region of a short dry 

 season. Thus Balanga (Bataan), in the region of the dry season, 

 has an annual rainfall of 2,394 millimeters (94 inches), of which 

 83.5 per cent, falls from June to October; 5.4 per cent, from 

 November to February; and 11.2 per cent, from March to May. 

 On the other hand, Jolo, in the Sulu Archipelago, with no dry 

 season at all, has an annual rainfall of only 1,666.8 millimeters 

 (65.7 inches), of which 49.2 per cent, falls from June to October; 

 83.5 per cent, falls from June to October; 5.3 per cent, from 

 from March to May. 



Although the Philippines have a range of latitude from 4.5° to 

 22° north, the variation in the temperature is believed not to be 

 great enough to have any pronounced direct effect on the vege- 

 tation below 500 to 600 meters (1,640 to 1,968 feet) in altitude. 



III. Philippine Forest Types. 



To one unfamiliar with tropical regions, the forests of the 

 Philippines present, in many places, such a tangled and luxuriant 

 mass of growth containing such a variety of tree species and other 

 plants that one is at first utterly confused and bewildered. Sys- 

 tematic study, however, reveals the fact that here, as elsewhere, 

 differences in environment produce differences in forest growth; 

 that forest types are generally well defined; and that often the 

 lines of distinction are clearly drawn. 



Five principal types of forest (one of these being really a 

 combination of four types) may be distinguished. The following 

 table names and gives a rough estimate of the area occupied by 

 each as well as their estimated volume in cubic meters and board 

 feet: 



