Current Literature 369 



4. The chief difference between the dipterocarp forest and a 

 hardwood forest of the temperate zone Hes in the several-storied 

 arrangement of the dipterocarp forest, with an accompanying 

 greater density of foHage, and in the presence of a much larger 

 number of minor tree species. 



5. Dipterocarp forests vary from dense stands in which the 

 main story is composed entirely of mature and overmature dip- 

 terocarps to more open stands in which the main canopy may 

 contain more individuals of other species than dipterocarps. 



6. The volume of a dipterocarp forest may be greater than that 

 of an all-aged managed stand in Europe, but is usually less. 

 When the volume is great its distribution is usually unsatisfactory 

 from a management standpoint, as the bulk of it is contained in 

 large mature and overmature individuals, the removal of which 

 causes the destruction of the forest. 



7. If the dipterocarp forest is removed and the land is not culti- 

 vated, the forest is replaced by a non-commercial one of a 

 totally different type in which the trees are of small, softwooded, 

 rapidly growing species. If, after the removal of the forest, the 

 land is cultivated and later abandoned, it usually grows up in 

 grass which maintains itself as long as it is burned over at more 

 or less frequent intervals. 



8. Dipterocarps growing in virgin forests in the Philippines 

 undergo an extremely long suppression period. After this sup- 

 pression period Parashorea plicata, the most rapidly growing dip- 

 terocarp measured, appears to grow about twice as fast as Yellow 

 poplar in virgin stands. The average of the dipterocarps meas- 

 ured shows rates of growth, after the suppression period, about 

 equal to those of hardw^oods in virgin forests in the central hard- 

 wood region of the United States. Parashorea plicata, on Mount 

 Maquiling, shows distinct seasonal rates of growth, there being 

 two periods of slow and two of rapid growth. One period of 

 slow growth coincides with the dry season, the other with the 

 height of the rainy season when the sky is overcast for a large 

 portion of the time. 



9. The temperature in the dipterocarp forest of Mount Maqui- 

 ling is very uniform and not particularly high. The daily range is 

 much greater in the dominant story than in the undergrowth. The 

 humidity and soil moisture under the forest are always high and 

 the rate of evaporation is low. The environment of the dominant 

 story is much dryer than that of the undergrowth. The rate of 

 evaporation, even in the top of the dominant story during the dry 

 reason, is not high when compared with evaporation rates in 

 deciduous forest regions in the United States. Environmental 

 conditions in the forest are apparently favorable for growth 

 throughout the year. The result is that such a dense vegetation is 

 produced that the rate of growth of the individuals is greatly 

 lowered. 



