474 The Philippine Journal of Science m* 



favorable conditions for growth which exist in the tropics and 

 that throughout the earlier period of their existence they main- 

 tain themselves and grow under very adverse conditions ; that is, 

 Parashorea in a virgin forest passes through an exceptionally 

 long suppression period as compared with trees in a deciduous 

 forest of the temperate zone. 



In as much as climatic data collected in the forest on Mount 

 Maquiling show that conditions are favorable for plant growth 

 throughout the year, it seems clear that this long period of 

 suppression must be referred largely to the lack of light under 

 the main canopy of the forest. A study of the curves for tem- 

 perate species, presented in connection with Parashorea in fig. 1, 

 shows that none of these species undergoes any considerable 

 I)eriod of suppression in youth. The curve for oak in Europe 

 would not be expected to have this suppression period, as it 

 represents a planted forest in which the crowns of the trees are 

 exposed to full overhead light throughout life. The curve for 

 yellow pine likewise shows no marked suppression period. This 

 is connected with the fact that the tree is one of exceptional 

 intolerance to shade, and grows normally in a very sparse, open 

 forest. The curves for white oak and yellow poplar are taken 

 from data collected from virgin forests in the United States 

 which are commonly considered dense deciduous forests for tem- 

 perate regions. Both of these species are rather rapid growing, 

 and the convex form of the curves would indicate very little in 

 the way of a suppression period due to shading. A comparison 

 of the form of the curves for these two species with that for 

 Parashorea seems to show that the density of the canopy of a 

 deciduous forest in the temperate zone is by no means so great 

 as is that of the dipterocarp forest of Mount Maquiling. 



It has been previously pointed out that the forest of Mount 

 Maquiling has a very open canopy as compared with the other 

 dipterocarp forests discussed and that the rates of growth ob- 

 tained for Parashorea are faster than those for any other 

 dipterocarp measured. It is to be expected from this that dip- 

 terocarps in most of the forests of the Philippines will show an 

 even greater suppression period than does Parashorea plicata on 

 Mount Maquiling. This would seem to be true in the forest of 

 Bataan (Table XXIII) where, according to the available figures, 

 the average dipterocarp is 116 years old when 5 centimeters in 

 diameter. 



The rapid growth made by young individuals of Parashorea 

 when growing in the open confirms our conclusion that the long 

 suppression period shown by forest-grown seedlings is due to a 



