PREFACE 



It is the purpose of the following pages to present a general 

 account of the forests of a region comprising about 175,000 square 

 miles lying across the Rocky Mountains south of the 49th parallel 

 and marked by great diversity of topography, soil and climate. 

 The many factors involved in the development and maintenance 

 of the present physiognomy of the vegetation merit careful study, 

 both as to the sources whence its component parts have been 

 derived and as to the agencies and conditions at present effective 

 in their local movements and inter-relations. It is designed to 

 open the way to a critical study of this area and to emphasize 

 the point of view from which this and all other such studies 

 should be approached. 



The usual approach to the study of problems in ecology, 

 both in matters of association and succession and of local and 

 general distribution has up to the present time been mainly 

 from the side of the physical factors involved, and hardly, if 

 at all, from the standpoint of individualities of the species con- 

 cerned. It is the intention herein to lay particular emphasis 

 upon the latter and, while taking account of the climatic and 

 topographic influences, to stress those characteristics of the most 

 important species as far as known, as furnishing the clue to the 

 solution of problems of competition and dispersal. It is but a 

 truism to say that the fuller the knowledge of the specific pe- 

 culiarities of a plant the more may its place in the flora be 

 understood. 



Acknowledgment of valuable suggestions and criticisms of 

 the manuscript by Prof. John W. Harshberger of the University 

 of Pennsylvania and Dr. Forrest Shreve of the Desert Laboratory 

 of the Carnegie Institution of Washington is due and is hereby 

 gladly rendered. 



J. E. KIRKWOOD. 



Missoula, Mont, May 1, 1922. 



