REPORT OF COMMISSION VII 
GVII-37 
for planning logging and cutting operations. Special maps with such units have 
been made during the last two years. The contact prints are first studied in a 
stereoscope; the watershed and drainage systems are then drawn on the prints; 
after that the forest is divided into treatment units. For each unit the kind of 
stands, the volume, the mixture of tree species, and sometimes also the plan for 
needful measures are noted. To get the correlation factor, some of the units are 
checked in the field. 
On an experimental district of 5,000 hectares, mapping of this kind has 
been carried on in the current year. The photographs were taken by the Geo 
graphical Survey Office on a scale of 1:25,000 The instrument for indoor work 
was a mirror stereoscope, model Old Delft. Every unit was checked in the field. 
A comparison between the values obtained by stereoscope and the field measure 
ment resulted as follows: 
1. Volume 
The total volume of the whole district was overestimated by 9.5%. The 
mean error was equal to +9 cubic meters per hectare. 
2. Kind of stands 
91% of the units was correctly identified. 
3. Mixture of tree species 
Tree species in majority: 94% correctly identified. 
Tree species in minority: 77% correctly identified. 
The efficiency of the stereo method was 1,500 hectares/day (6 hours a day). 
The character of the district somewhat favored identifying stands and tree spe 
cies; the southern part consists merely of old stands of spruce while the northern 
part is mainly a middle-old stand of pine. The volume was throughout overrated 
probably because of the lateness of the photography (3 p.m.). The quality of 
the prints was otherwise very good. 
A ranger district was estimated by photo interpretation. Photos of the Geo 
graphical Survey Office, photographed in 1949 to a scale of 1:20,000, were used. 
The needed instruments were a mirror stereoscope and a pocket stereoscope. 
The estimation was carried out by the field. A comparison between the photo- 
scopic and the field estimation gave the following results: 
1. Site 
The greatest difference with respect to the total areas in the different site 
classes was +5%. The medium site in photo estimates was 3.7 cubic meters per 
hectare, and in the field measurements 3.6 cubic meters per hectare. 
2. Kind of stands 
The difference between the principal types was very little, 2 to 3% for the 
young thin stands. The different types of mature stands and cleared areas under 
different stages of reforestation were not satisfactorily identified due to the 
photographs not being up to date. 
3. Plan for logging 
The logging plan for the different stands was proposed on stereo prints. 
This method compared favorably with the field plans. 
4. Barren land 
By stereoscopic method 
In field measurement 
Swamp forest 
6% 
4% 
19% 
17%