IX, A, 6 Brown and Mathews: Dipterocarp Forests 531 



Livingston ^^ gives the rates of evaporation at a number of 

 stations in the United States for the period from May 25 to 

 September 7, 1908. He says: "The deciduous forest of the mid- 

 dle east occupies a region with over 100 cc, often over 150 

 and even 200 cc, as the mean weekly summer rate." These 

 results are not directly comparable with those from Mount Ma- 

 quiling as they were obtained from atmometers placed 15 cen- 

 timeters above the ground in the open and with free access 

 to sun and wind. A comparison of the highest rates obtained 

 on Mount Maquiling with those from the United States, how- 

 ever, seems to show that the rate of evaporation from the top 

 of the dominant story on Mount Maquiling is not particularly 

 high even during the height of the dry season. It has already 

 been pointed out that the moisture content of the soil is high at 

 all times of the year. This indicates that conditions in the forest 

 were not excessively dry even at the height of the dry season. 

 It should be remembered, however, that the effect of the dry 

 season on the vegetation is very marked. We have already seen 

 that Parashorea plicata shows a very slow rate of growth at this 

 time. The main canopy of the forest, while by no means 

 deciduous, is much less dense during the dry season than at 

 other times, while small herbs may wilt or even dry up 

 completely. 



The foregoing discussion of environmental factors in the 

 forest of Mount Maquiling seems to indicate that the conditions 

 were very favorable for the development of a luxurious vegeta- 

 tion and for rapid growth. The forest of Mount Maquiling is 

 very open as compared with a well-developed dipterocarp forest, 

 but is very dense in comparison with a deciduous one of a temper- 

 ate zone. We have already seen that Parashorea plicata grows 

 from 30 centimeters to 70 centimeters in diameter in fifty years, 

 while it takes yellow poplar, the fastest growing temperate-zone 

 species considered in this paper, one hundred fifteen years to 

 make the same growth. This rapid growth is, however, not 

 equaled by smaller individuals of Parashorea nor by other dip- 

 terocarps where growth has been studied in denser forests. 

 According to our calculations it takes a seedling of Parashorea in 

 the forest sixty-two years to become 5 centimeters in diameter. 

 This slow rate of growth is due to the density of the forest, 

 and it is probable that the same conclusion will hold for the 



" Livingston, B. E., A study of evaporation and plant distribution, Plant 

 World (1911), 14, 205. 



