EESEAECH METHODS IN STUDY OF FOREST ENVIRONMENT. D 
breeding. On the other hand, the environment of this entity can 
to a considerable degree be controlled, and its reactions to changes 
in environment can be observed. His concern is therefore not with 
the physiological functioning of the plant as such, but with its 
physiological functioning in relation to a given environment. 
Control of environment is the cornerstone of the practice of 
forestry. The art of the forester is primarily the art of utilizing 
to best advantage the biological forces active in forest growth, 
through his ability to modify the environment. Any considerable 
use of forests means interference with the natural conditions and 
modification of some of the environmental factors, the sum total 
of which determined the character of the present forest. Forestry 
adapts this interference to produce the best results, from the stand- 
point of human needs. Therefore it has been thought best in this 
bulletin to take up each of the environmental factors separately, 
and to introduce only such a discussion of physiological facts as 
seems necessary to a proper conception of the methods of study of 
the environment. 
Ecological forest studies deal with all problems which involve the 
determination of the effect of environmental conditions on repro- 
duction, initiation, growth, and physiological functions. To this 
group belong such studies as the seed production of different species 
in different seasons and conditions; the characteristics of seeds as 
related to their origin ; the correlation between the composition, suc- 
cession, and growth of forest vegetation on the one hand, and the 
conditions of the evironment on the other; the vast field of prob- 
lems in natural reproduction and methods of cutting for definite 
silvicultural purposes; the various phases of forestation, including 
the germination of seed, requirements for shade and water of the 
different species, the planting of forest trees, and their competition 
for moisture and light with herbaceous and shrubby vegetation ; and 
many similar problems. The methods and instruments available for 
the study of the ecological forest problems are essentially the same 
as those which are used in the study of the physiology and ecology 
of plants in general. They involve the measurements of such aerial 
conditions as precipitation, air temperature, the evaporating power 
of the air, wind velocity and wind direction, and sunshine intensity ; 
and such subterranean conditions as temperature and moisture of 
the soil, its depth, structure, and chemical composition. The func- 
tioning of the tree in response to these conditions must also be meas- 
ured by the means recognized and used by plant physiologists. The 
methods and instruments used in physiology, meteorology, and soil 
physics, therefore, are applicable in a large measure to the study of 
ecological forest problems, though often with modifications necessi- 
tated by the character of the plant and of its environment. 
