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 may 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 TO feet, the observations 



should be at 104-' J ~ 1U or 40 feet from the ground. Measurements 

 2 



of the light received by the stand should obviously be made at an 

 elevation wliere 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 -jo or 30 feet to be always equal to the local mean annual 

 temperature. Similarly, soil moisture may be determined at the 

 -hi tare and at 1. -J. •".. 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. 



mm \no. oi INSTRUMENTS FOB THE STUDY OF CONDITIONS AFFECTING 



REPRODUCTION. 



h i- only logical to assume that, before a definite plant formation 

 or fores! type can be developed, there must exist conditions favorable 



