532 The Philippine Journal of Science in* 



slow rate of growth shown by trees in denser forests, for while 

 environmental data are lacking for these forests it does not 

 seem likely, nor do our observations seem to show, that these 

 regions which have produced forests denser than that of Mount 

 Maquiling have climates which are naturally less favorable for 

 growth. The density of the forests undoubtedly greatly reduces 

 the amount of light received by all except the largest trees, 

 while at the same time there must be severe competition among 

 the roots of the vegetation. It is to be expected, therefore, that 

 if suitable trees were grown in plantations in such a way as 

 properly to regulate the density the resulting growth would 

 be very rapid. This conclusion is confirmed by the rapid rates 

 of growth shown by Parashorea growing in the open and by 

 the even faster development of second-growth trees. 



Results which have been obtained in plantation work by the 

 Bureau of Forestry are also in accord with this view. 



One of the most striking things about the forest of Mount 

 Maquiling is the great difference between the conditions in the 

 dominant story and in the undergrowth. The most obvious dif- 

 ference is that of light. The dense canopy which cuts down 

 the amount of light entering the undergrowth has a similar 

 effect on the wind, the undergrowth being at most times remark- 

 ably still. The fact that comparatively little wind enters the 

 undergrowth probably has a decided effect on the temperature 

 in it. This temperature has a lower average and is much 

 more constant than that in the dominant story. Our records 

 of evaporation show a rate in the top of the dominant story 

 which is, on the average, more than six times as great as that 

 in the undergrowth. These rates, being from white surfaces, 

 do not take into account sufficiently the difference due to sun- 

 light, so that the actual difference between the rates of evapo- 

 ration in the two situations is even greater than that indicated. 



When we consider the differences between the conditions in 

 the undergrowth and in the dominant story, it would not be 

 surprising if plants which had developed in the former were 

 unable to stand the conditions in the latter. When the main 

 canopy is removed, the plants which are left are subjected to 

 conditions at least approaching those to which the dominant 

 story is exposed. We have seen that the removal of the main 

 canopy is usually followed by the death of most of the trees and 

 seedlings which remain. If the only difference between the 

 conditions to which these were exposed before and after the 

 removal of the main canopy was that of evaporation, this alone 

 would probably, in most cases, be sufficient to cause their death. 



