IX. A, 6 Bi'ovm and Mathews: Dipterocarp Forests 525 



cubic meters. It would appear from this that under any rational 

 system of management we can increase our timber production 

 about fifty-six times without in any way reducing our forest 

 capital. 



ENVIRONMENTAL CONDITIONS IN THE FOREST 



The measurements of environmental factors here recorded 

 were made on a ridge in the dipterocarp forest of Mount Ma- 

 quiling, at an elevation of approximately 300 meters, and near 

 the region in which growth measurements were taken. They 

 cover nearly the same period as do the records of seasonal 

 growth. 



In discussing the distribution of dipterocarp forests in the 

 Philippines, it was shown that the temperature at low elevations 

 was remarkably uniform throughout the Archipelago and so its 

 variations could hardly have any considerable influence in pro- 

 ducing the diflferences between the types of vegetation which 

 cover large areas in the lowlands. The temperature in the 

 forest, however, will have to be taken into account in any ex- 

 planation of the rates of growth shown by the trees. 



Records of temperature in the forest of Mount Maquiling were 

 taken about 75 centimeters above the ground by means of a 

 Draper's recording thermometer. The results are presented in 

 Table XLII in the form of maxima, minima, means, averages 

 of daily maxima, and averages of daily minima for periods of 

 ■four weeks. The means were taken from the original auto- 

 matically traced records by means of a planimeter, and for this 

 reason should be highly accurate. An inspection of Table XLII 

 brings out two points: the temperature is remarkably uniform 

 and it is not extraordinarily high. The mean temperature 

 from January 3, 1913, to January 2, 1914, was 23°. 1. The 

 maximum for the year is 29°. 7 and the minimum is 19°. 4, the 

 yearly range being 10°. 3, The highest mean temperature for 

 any of the four-week periods is 25°. 1 and the lowest is 21°.7. 

 The daily range is likewise small. The average maximum for 

 the year is 25°. 1 and the average minimum is 21°.6, making the 

 average daily range 3°. 5. 



These figures show that the temperature under the forest cover 

 is high enough at all times of the year to make growth possible. 

 The temperatures, however, are never as high as those which 

 are regarded as optimum for rapid growth, and for most of the 

 time are probably about 10° below the optimum. 



It is difficult to compare the effectiveness of temperature in 



