6 BULLETIN 1059, IT. S. DEPARTMENT OF AGRICULTURE. 
While it is true that in studying the present composition of a 
forest stand it is necessary, to a certain extent, to have the historical 
viewpoint in order to determine clearly how this stand was initiated 
and why it now supports one dominant species rather than another, 
still it must be recognized that historical studies and conjectures are 
outside the main domain of ecology. The purpose of ecology as an 
exact science must always be to measure present conditions and 
their reactions on the organism, reducing to precise terms relations 
between environment and life which may be already understood in 
general terms. In such processes no distinction will be made between 
a condition which is a direct result of the climate or site, one which 
is the result of cumulative effects of the presence of the plant forma- 
tion, and one which may represent the current influence of the pres- 
ent plant formation. Thus, while recognizing in principle and in 
the application of results historical conditions and the so-called 
social relations which are particularly important in forest aggrega- 
tions, it must be clearly understood that, in the current measure- 
ments with which this bulletin has to deal, the source of a given con- 
dition has no bearing on the method of its determination. 
SAMPLE PLOT METHOD COMMON TO BOTH ECOLOGICAL AND STATISTICAL 
STUDIES. 
A method common to both ecological and statistical problems is 
the method of sample plots. The details of the sample plot method 
vary with the purpose of the problem which is being investigated. 
The plot may vary in size from a square foot to an entire section. 
It may have all possible geometrical forms — circle, square, quad- 
rangle, strip, or triangle. It may be used in the study of herbaceous 
vegetation, of seedlings in a nursery, or of virgin forests; for the 
purpose of studying the evolution of the vegetation, for bringing out 
the effect of a definite condition, for determining the growth of the 
vegetation, or for observing any other change that takes place in 
the plant association, whether it be grass, brush, or forest. The prin- 
ciple, however, remains everywhere the same; namely, the use of 
areas representative of a given type of vegetation for intensive obser- 
vation over a long period of time. 
NEED FOR A PERMANENT ORGANIZATION IN FOREST INVESTIGATIONS. 
The great variety of forest stands, the difference between stands in 
different regions, and the longevity of trees make it difficult for an 
individual to complete any investigation on the life of the forest. 
This difficulty is now universally recognized. A permanent organi- 
zation charged with such investigations has been formed in practi- 
cally every country in which the care of the forests is a matter of 
national concern. This permanent organization consists of investi- 
gators assigned to forest experiment stations. 
