EESEAECH METHODS IX STUDY OF FOREST ENVIRONMENT. 11 
reached, as it is then limited in its extensions for light and soon can 
not make the needed annual additions to its transporting system. 
It is hoped that this discussion will clarify the point of view which 
prevails in the discussion of the individual environmental conditions. 
MEASUREMENT OF ENVIRONMENTAL CONDITIONS 
AFFECTING FOREST VEGETATION. 
The character of the forest and its very existence are determined 
by the climate, soil, and subsoil of the locality. The general charac- 
ter of the region, including the character of the vegetation and of 
the soil, is determined in the highest degree by the climate. The 
climate affects the region and vegetation in two ways: (1) It is at 
present the most important factor in the environment of the vegeta- 
tion: (2) it has affected the present environment in its historical de- 
velopment ; for instance, in the formation of the soils, their present 
physical and chemical composition being largely the result of the 
past climate in combination with other natural factors. The deter- 
mination of the important features of a climate is not a simple mat- 
ter. It must rest upon a sufficiently long series of observations at 
well-equipped meteorological stations. 
CLIMATIC CHARACTERISTICS OF LOCALITY. 
NATURAL CLIMATIC REGIONS. 
The characteristics of a climate must be studied first of all by 
natural regions and the study based on the observations of several 
stations located in different parts of the same region. The climate of 
individual localities may best be analyzed by comparison with the 
climate of the entire natural region in which the locality is found or 
of a control station centrally located. 
DATA OBTAINED BY WEATHER BUREAU. 
For general climatic studies of the forest regions, and to some 
extent in studying the conditions for growth in established stands, 
the data collected by the United States Weather Bureau at its numer- 
ous regular stations may be used to good advantage. At the greater 
number of these stations only data on air temperatures and precipita- 
tion are obtained. At the larger stations data on humidity, sun- 
shine, barometric pressure, etc., are obtained, but because of the al- 
most universal location of such stations in towns and cities the 
applicability of the data to forest conditions is often very question- 
able. It appears, therefore, that the regular observations of the 
Weather Bureau will furnish us principally with precipitation and 
temperature data by which the broader forest regions may be da- 
