488 



The Philippine Journal of Science 



lau 



A study of the curves for type area B shows that not one 

 of the species dominant in this forest is as successful in its 

 growth as are the temperate species. Data for the rate of 

 growth of Shorea polysperma (tanguile) are lacking for the 

 larger size classes, and as the curve of growth for this species 

 crosses that of white oak at the age of 132 years when it 

 has reached the diameter of 43 centimeters it is possible that 

 this species might in later years prove more successful; but, 

 from the data at hand, no such conclusion can be drawn. It will 

 be noted from the curves that the average rate of growth of all 

 dipterocarps is only about half that of yellow poplar. Thus, 



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Fio. 4. Rates of growth of trees. Type area A, Bataan Province, Luzon. 



yellow poplar grows from 5 to 60 centimeters in one hundred 

 thirty-three years, while the average dipterocarp requires two 

 hundred sixty-seven years to make the same growth. Diptero- 

 carpus grandifloms and Pentacme contorta, which are very 

 prominent in this region, grow at a very much slower rate. 

 Owing to the presence in this dipterocarp forest of a dense 

 mass of foliage which is not producing commercial timber, it 

 is not to be expected that the density of the dipterocarp forest 

 will counterbalance the slow rate of growth in producing a 

 volume of timber per year equal to that produced by good forests 

 in the temperate zones. It is possible that under management 

 a pure dipterocarp forest of the most successful species of the 



