10 The Philippine Journal of Science 1923 



is 30 meters high but, with the intrusion of the dipterocarps at 

 and below 1,060 meters, the height abruptly increases to 60 

 meters. 



In most dipterocarp forests the ground is bare and herbs 

 are scarce. In the Quercus-N 'eolitsea association of the mid- 

 mountain forest there is in most places a well-developed 

 ground covering of herbs. The change takes place not in the 

 tension zone between the two associations but in the upper part 

 of the dipterocarp forest. Brown further calls attention to the 

 fact that the midmountain forest is more open than the diptero- 

 carp forest, but here again the change is a gradual one and begins 

 in the upper part of the dipterocarp forest ; he states, further- 

 more, that the increase of epiphytes is much greater in the 

 midmountain forest, this being due to the general complex of 

 conditions that cause increased epiphytic vegetation as higher 

 altitudes are reached. There is no marked change either in 

 amount or composition of this vegetation on the border between 

 these two associations. In these midmountain forests there are 

 no dominant trees corresponding to the dipterocarps in the 

 forests at lower altitudes. 



To those unacquainted with the primary forests of India and 

 Malaysia it is difficult to convey an impression of how absolutely 

 dominant the dipterocarps are in these vast forested areas. 

 Brandis has emphasized the fact that numerous species are 

 gregarious, forming nearly pure stands of large extent where 

 single species occur to the practical exclusion of all others. He 

 is entirely correct in his statement that the dipterocarps in the 

 tropical forests of eastern Asia play the role which in Europe 

 (and for^that matter North America) belongs to the Coniferae 

 and Cupuliferae. The most noted gregarious species is the sal, 

 Shorea robusta Gaertn. f., which forms pure or nearly pure 

 forests of vast extent in the Himalayan foothills and in eastern 

 central India. Brandis enumerates seventeen species in seven 

 genera that are known to be gregarious. In addition to these 

 gregarious species very many more are semigregarious • but 

 practically wherever they occur, even though as scattered 'indi- 

 viduals, they dominate and give character to the forests on 

 account of their great size (see Plates 3-8). 



Owing to the fact that these forests contain a high percentage 

 of commercial timber, they have been intensively studied in 

 India, Malaysia, and the Philippines. The Philippine diptero- 



