STUDIES IN THE VEGETATION OF THE PHILIPPINES, I. 723 
of the time they require in regions where the climatic conditions inhibit 
growth entirely for a considerable part of the year. If bulk alone is 
considered as a measure of success in forest growth, the virgin forests 
of some parts of the temperate regions are surely more successful than 
those of the tropics. This is especially true of the northwestern part of 
the United States where exceedingly heavy stands of coniferous forests 
occur. But if the annual increment is also used as an element of success 
it is believed that some tropical regions are capable of producing more 
bulk jjer year than temperate regions. Again, this is of economic 
importance. While the land area of the north temperate zone is much 
greater than that of the tropics and the absolute forest land (that is land 
that is better fitted for forest growth than agriculture) is also much 
greater, this inequality is in a measure offset by the possibility^ that each 
acre of land in the tropics can probably produce from one and a half to 
two crops of timber for one crop in temperate regions. A theoretical 
discussion of the causes of the shorter lives of tropical trees is reserved 
for another paper. 
I wish to express my 'thanks to E. D. Merrill, Botanist of the Bureau of 
Science, for assistance in referring tree species to their scientific names, 
and especially to H. M. Curran, Forester in the Bureau of Forestry, for 
valuable suggestions in the preparation of this paper. 
