14 INTRODUCTION. 



This is briefly recorded for the benefit of those who desire just this 

 information. But for the benefit of very many more it has seemed 

 proper to include also a brief detailed description of the local range, 

 vertical and horizontal, by States, Territory, and other geographical 

 subdivisions in the region occupied by the species or subspecies. The 

 fullest information possible has been given for commercial trees. 



A very much more definite knowledge is greatly and generally 

 needed of the local distribution of our trees. Extreme extensions or 

 outlying stations for each tree require to be recorded. No observers 

 have done more along this line than authors of State and county 

 floras, by whom actual limits of range have been carefully worked 

 out for the trees and other plants of their special localities. There 

 are too few of these painstaking workers, and their work can not be 

 too highly praised. The writer wishes to emphasize the fact also that 

 the numerous unpublished silvical, National Forest boundary, and 

 other field reports by members of the Forest Service, as well as 

 special field reports by members of the U. S. Geological Survey and 

 the Biological Survey, have proved rich sources of new information 

 on the local and general range of Pacific trees. Through these sources 

 the distribution of some trees has been extended hundreds of miles 

 beyond previously recorded limits. Finally, it is hoped that by giv- 

 ing, in detail, what is now known the many observers and lovers of 

 trees who are scattered throughout this region will be stimulated to 

 make further contributions. Much is yet to be learned of where the 

 trees of this region grow. 



OCCURRENCE OF TREES. 



Closely connected with a study of the areal and altitudinal range 

 of trees is the equally important determination of where, in their 

 respective ranges, this or that species lives — by necessity or by virtue 

 of special fitness. Like animals, trees have what may be termed a 

 more or less definite habitat, defined by such physical conditions as 

 soil, moisture, topography, and, to a greater or less extent, tempera- 

 ture. The likes and dislikes, as it were, of one species are, of course, 

 shared by a number of others, so that several species may have their 

 habitat in wet, in moist, or in dry situations; while different indi- 

 viduals of the same species may accommodate themselves to all of 

 these situations. 



It would lead too far, for present purposes, to discuss, even briefly, 

 the factors upon which the adaptation of trees to environment appear 

 to depend. The effects of mutual likes and dislikes upon species 

 are to be seen in the occurrence of certain trees in pure stands only 

 and the occurrence of others with different kinds of trees or with 

 different species of the same kind. 



