RESEARCH METHODS IN STUDY OF FOREST ENVIRONMENT. 13 
periods of plant activity may be employed in summarizing tem- 
peratures, etc. 
SPECIAL OBSERVATIONS ON CLIMATE AND SOIL OF LOCALITY. 
To obtain concrete information on restricted localities and specific 
forest types it will be necessary in most instances for forest investi- 
gators to establish apparatus and make observations independently. 
In the more important respects the accepted procedure of meteor- 
ologists and the standard instruments ma}^ be used by the forest 
investigator, but the latter will also require many data not obtained 
in routine meteorological work, and, especially in the location of 
instruments, will be compelled to vary procedure according to local 
needs. 
LOCATION OF INSTRUMENTS FOR THE STUDY OF THE GROWTH OF FOREST STANDS. 
Atmospheric conditions affecting the growth of forest stands as 
a whole should naturally be measured at a distance from the ground 
which will represent the mean height of the sensitive portion of the 
tree; that is, the mean elevation of the crown. Thus, if a stand 
were generally devoid of green limbs for the first 10 feet of the 
stems and had an average total height of 70 feet, the observations 
should be at 10-f , or 40 feet from the ground. Measurements 
of the light received by the stand should obviously be made at an 
elevation where none of the light is intercepted. The same result 
may sometimes be obtained by measurements near the ground in a 
large opening on the same site. Soil conditions should be measured 
at all depths which the roots of the trees may be reasonably ex- 
pected to reach. The depth will be less in heavy than in light soils. 
In general, however, it is believed that an extreme depth of 4 feet 
is sufficient, though any evidence to the contrary should change the 
procedure. The rule of measuring soil temperatures at the surface 
and at 1 and 4 feet may be followed. If it should appear necessary 
in using the data, the temperatures at other depths may be obtained 
by plotting the known values and by interpolating on the curve 
which may be drawn for any given period, assuming the tempera- 
ture at 20 or 30 feet to be always equal to the local mean annual 
temperature. Similarly, soil moisture may be determined at the 
surface and at 1, 2, 3, and possibly 4 feet and, by projecting the 
curve formed by plotting the moisture of these points the moisture 
at greater or intermediate depths may be approximated. 
LOCATION OF INSTRUMENTS FOR THE STUDY OF CONDITIONS AFFECTING 
REPRODUCTION. 
It is only logical to assume that, before a definite plant formation 
or forest type can be developed, there must exist conditions favorable 
