vs., A, 5 Brown and Mathews: Dipterocarp Forests 513 



creased due to increased cloudiness, the amount of light is less 

 and the humidity is higher. Accompanying this is a reduction 

 in temperature. It is to be expected that the reduction in the 

 amount of light and the lower temperature will be reflected 

 in a slower rate of growth, and such meager data as have 

 been collected bear out this expectation. In Table XXVI are 

 presented figures for the growth of all dipterocarps measured 

 on type area C at an elevation of approximately 700 meters on 

 Mount Mariveles, Bataan, and in Tables XXXIII and XXXIV 

 similar figures for the miscellaneous trees of class II and class III 

 are given. An examination of these tables shows very little 

 difference in rates of growth between dipterocarps and the other 

 tree classes, and the rates of growth shown therein are notably 

 slow. When compared with the growth of yellow poplar, we 

 find that it takes an average dipterocarp three hundred eighty- 

 three years to grow from 10 centimeters in diameter to 40 centi- 

 meters, whereas it takes the yellow poplar but seventy years to 

 make the same growth. The figures on which these results are 

 based are too few to have great reliance placed upon them, but 

 it is not probable that any error which may enter into the re- 

 sult will be sufficient entirely to vitiate them. It seems to be 

 quite clear that above elevations of 600 meters little can be ex- 

 pected from forests in the Philippines in the production of com- 

 mercial timber under any reasonable rotation. A striking fact 

 which is suggested by the tables for species at this elevation is 

 that even in a virgin forest there is probably little difference in 

 the rates of growth of trees in the dominant class and those of 

 classes II and III. The forest is, of course, more open than that 

 at lower elevations, and the composition is less complex. This 

 accounts in part for the ability of species of tree classes II and 

 III to maintain rates of growth similar to that of trees of the 

 main canopy, but it is also probable that conditions of growth 

 have so changed from the optimum for dipterocarps that they 

 have been reduced in their rates of growth to approximately 

 the same as those of the second- and third-story trees which are 

 more at home at this elevation. 



We have already noted that the dipterocarps apparently show 

 a more rapid rate of growth in open than in dense forests and 

 that removing part of the main canopy, as in the case of type area 

 A and the trail trees in Bataan, increases the rates of growth of 

 tree classes II and III. These points are emphasized in the 

 curves in which the rates of growth of the same tree class in 

 different areas are compared. Comparing the rates of growth 



