490 ^^2.6 Philippine Journal of Science i9u 



terocarps to grow from 10 to 80 centimeters on type area A is 

 two hundred forty-two years and on type area B two hundred 

 eighty-one years. The growth of dipterocarps of diameters 

 larger than 20 centimeters on the two areas shows even greater 

 similarity as will be seen by referring to fig. 6, in which are 

 plotted the average rates of growth of all dipterocarps above 

 20 centimeters for each of the areas considered. 



A number of trees were measured at elevations of from ap- 

 proximately 50 to 100 meters on a trail leading up to type area 

 A. Here the forest has been very badly cut over and has 

 been very largely replaced by a growth of Schizostachyum 

 mucronatum (boho). The only dipterocarps measured were 

 large ones, which for the most part overtopped the boho. The 

 average yearly rate of growth for the dipterocarps is given in 

 Table XXV, and the curve of growth appears in fig. 5. It will 

 be seen from the curve that the trees along the trail, all of 

 which are more than 20 centimeters in diameter, show a rate 

 of growth greater than those on either type area A or B and 

 approximately equal to those in northern Laguna. This increased 

 rate of growth is shown in all size classes from 20 centimeters up, 

 and is probably due in part to the more favorable situation at 

 lower elevations and in part to the opening up of the forest. 



In fig. 6 the rates of growth of dipterocarps more than 20 

 centimeters in diameter, on all of the areas under discussion, 

 are compared with each other and with the rates of growth 

 of yellow poplar and white oak. An examination of this figure 

 shows that the larger individuals of the dipterocarps on type 

 areas A and B in Bataan grow about as fast as white oak ; that 

 those in northern Laguna and the trail trees in Bataan make 

 a more rapid growth, which is about equal to that of yellow 

 poplar; and that Parashorea plicata is the fastest growing of 

 all the species under discussion. 



The last area to be considered is that of type area C, lying 

 above type area B, at an elevation of 700 meters. Table XXVI 

 contains figures on the rates of growth of dipterocarps at this 

 elevation. This area is near the upper limit of the dipterocarp 

 forest, and as is to be expected the average rate of growth of dip- 

 terocarps as shown therein is very much slower than that at the 

 lower elevations. 



We have thus far been considering only the rates of growth 

 of our main crop, the dipterocarps, and have left out of consid- 

 eration the rates of growth of trees of the second and third 

 classes. The understories must, however, be taken into con- 

 sideration. In heavy dipterocarp forests their bulk is incon- 



