partic- 
lm as a 
1) has 
North- 
ous de- 
vegeta- 
| see in 
can be 
rencies 
) direc- 
rinfra- 
we find 
g when 
e tonal 
  
  
  
  
Xe 
land soil 
scientists 
s exactly 
hardwood forest on north (moist) and south (dry) slopes. Original panchromatic p 
U. S. Department of Agriculture. 
  
    
  
   
  
  
  
   
  
  
  
  
  
  
  
   
    
   
   
   
   
   
  
  
     
   
    
  
    
   
PHOTO INTERPRETATION IN FOREST INVENTORIES 
  
Fic. 4. Stereogram illustrating changes in forest due to past treatment. (1) Conifers originat- 
ing on abandoned fields, (2) conifers originating on natural openings in the forest, and (3) original 
hoto 1:20,000, 
variations as valuable to the forester as other, more complicated photog- 
raphy. 
A few species can be identified by means other than the tone of photos. 
The umbrella-like shape of the elm and the needle points of some conifers 
cast easily recognized shadows. White pine and aspen-birch may be separated 
by noting relative sizes, and some conifers may be recognized by the even 
photo texture of their small crowns in contrast with more coarse texture of 
the hardwoods. However, since it is not possible for the interpreter to iden- 
tify all species on photos, he may have to approach the problem indirectly 
through forest sites. 
Forest siles.—Under stereo even minor topographic differences are ac- 
centuated on aerial photos. Geologists and soil scientists have long recog- 
nized that these topographic differences are good indicators of basic soil 
conditions. Since forest types, as well as size, quality, and rate of growth, are