Apr. 14, 1923 
Physiological Requirements of Rocky Mountain Trees 99 
OBJECTS OF THE PRESENT STUDY 
Having now shown in a general way the nature of the problem which is 
constantly under consideration by students of ecology and forestry, the 
purpose of the study (one phase of which is covered by the present paper) 
may be definitely stated. As a matter of fact, it has several purposes, 
which are by no means distinct, but worthy of individual enumeratiom 
1. To compare the environments of the several species of trees with 
respect to each condition which may be separately measured, in order to 
determine what particular conditions have the most important bearing 
on the initiation of new stands, favoring one species rather than another. 
2. After noting the differences in the conditions of the various types, 
which really indicate differences in the physiological functioning of the 
species, to determine experimentally the degree of such differences as may 
exist between the species, and, as a result, the degree of difference in the 
actual requirements of the species for optimum growing conditions. This 
second object can hardly be attained in the field without most extensive 
long-term study, and necessarily resolves itself into experiments under 
controlled conditions of temperature, light, moisture, etc. The present 
paper deals largely with the results of such experiments. 
3. To describe the conditions of the various forest types of the region 
in such a manner as will explain most clearly the reasons for the success or 
failure of artificial forestation, so far as these may result from the environ¬ 
ment, and the conditions and means necessary for successful natural 
regeneration after fires or cutting. Here the object is to lead away from 
empiric silvicultural systems'" and toward the attainment of definite 
environmental conditions in all silvicultural practice. 
4. To convey a conception of the conditions under which the Rocky 
Mountain forests exist—that is, a view of th^ climatic and soil conditions 
of the forest region as a whole. 
It is needless to state that not all of these objects have been attained in 
the present work, which should be considered as something of a pioneer 
effort, merely blazing the way for much greater efforts and more refined 
methods which are necessarily for the future to bring forth. The hope 
may be justified, however, that the results and conclusions of this study 
will add somewhat to the information on the general subject and encourage 
the doing of more intensive work. 
SCOPE OF WORK 
The entire work, of which this paper represents only a part, is mainly 
a study of the physical environments of a number of different forest 
types in Colorado and Wyoming. The detailed study of the composi¬ 
tion of these several types has not been given a great deal of attention. 
Since the forest conditions are common ones and are frequently encoun¬ 
tered in the region, it is believed that the indications of prevailing com¬ 
position and of changes in composition, as they may be expressed in 
general terms, will be as valuable for present purposes as tabulated 
statements of the number, size, and kind of trees found at the several 
stations. The observations of meteorological conditions and of certain 
soil conditions thought to be fully as important, have, therefore, com¬ 
prised the major part of the field work. 
However, the early efforts (j) ® to summarize and compare these site 
conditions, as given in meteorological and soil records, and to deduce 
» Reference is made by number (italic) to “literature cited,” p. 163-164. 
