IX, A, 5 Broivn and Matheivs: Dipterocarp Forests 469 



occupy a dominant situation in the forest. Class II includes all 

 those which at maturity are subdominant; that is, which even 

 when fully developed have their crowns overtopped by the trees 

 of Class I, but which are still considered to be in the dominant 

 story. Class III includes those species which at maturity have 

 their crowns spread at a considerable distance below the main 

 canopy and belong in the second story. They are distinctly 

 tolerant of shade throughout life. Class IV comprises the re- 

 mainder of the plants of tree habit in the forest, which ordinar- 

 ily do not become much over 10 or 12 meters in height. These 

 constitute the third story. Tables for each of the above tree 

 classes were prepared similar in form to the tables previously 

 constructed for individual species. These tables show the an- 

 nual rate of growth, for each 10-centimeter class, of trees which 

 occupy practically identical situations in the forest. 



The average rate of growth of each class can be taken to 

 represent the rate of growth of that class in the forest. In order 

 to approximate the total ages of trees of different sizes in the 

 forest, the average annual rate of growth of each 10-centimeter 

 class was divided into 10 centimeters and the quotients assumed 

 to be the number of years necessary for the species or group of 

 species in question to pass through a 10-centimeter diameter class. 

 Summing up these quotients for the smaller sizes, we obtain a 

 figure which represents the age of our species or group of species 

 for any 10-centimeter size class; that is, the quotient obtained 

 by dividing the annual growth of the size class from 1 to 10 

 centimeters into 10 centimeters may be assumed to be the age 

 of a 10-centimeter tree. Adding this quotient to the quotient 

 obtained in a similar manner for the 10- to 20-centimeter class 

 we have the age of a 20-centimeter tree. In order to obtain 

 figures of the age of trees of any size and to present the above 

 data in graphic form, curves of diameter growth on age were 

 constructed by plotting this data on cross-section paper, the 

 ordinates of the curves being diameters and the abscissae being 

 years. For convenience in comparing the rates of growth of 

 various species in the Philippines with those of the temperate 

 zone, there have been plotted, in connection with these curves, 

 growth curves for hardwoods in the virgin forest of the central 

 hardwood region of the United States. The data for these 

 growth curves of temperate species are taken from Graves and 

 Ziegler." 



" Graves, H. S., and Ziegler, E. A., The woodman's hand book, Bull. U. S. 

 Forestry Sur. (1910), 36, 189-190. 



