COMMISSION VII: INTERPRETATION OF VEGETATION 
forest than obtainable by field reconnaissance. 
The modern forestry techniques demand 
larger working areas and a more careful plan- 
ning of the operations, and these aerial photo- 
graphs are a matter of necessity. 
Air photographs stereoscopically-viewed 
are mainly used for identifying forest areas in 
an unsatisfactory condition, for planning 
cutting areas, reconnaissance of marking 
areas, planning logging and reconnaissance of 
forest roads. 
In the northern parts of Sweden where the 
forest areas are more extensive and more diffi- 
cult to reach, the benefit of using air photo- 
graphs is greater than in the southern parts. 
The methods of stand and forest type class- 
ification vary greatly. On broad lines such 
classification can be done directly on the air 
photo but if greater accuracy is required more 
or less field checks are necessarv. 
No special air volume tables have been con- 
structed for Swedish conditions. Volume esti- 
mations from air photographs are done by 
using ordinary tables according to stand 
height and density. The accuracy of volume 
estimations from air photographs amounts to 
about 1095 as mean value for large areas. 
When greater accuracy is necessary field 
survey is required. 
Research has been carried out in order to 
ascertain the accuracy of measuring tree 
heights and stand heights on air photographs 
at different scales. The results have not 
vet been compiled. Other research is con- 
tinuing in order to find out the accuracy of 
estimating different stand factors from air 
photos (scales 1:10,000-1:30,000). The in- 
tention is also to attempt to ascertain more 
factors that can be identified on the photos, 
and which can facilitate for instance volume 
estimation and site classification For the ex- 
periment a great number of sample plots has 
been measured in the field with high accuracy. 
An experiment has also been started to 
find methods which can facilitate forest plot 
survey (with the air photos). 
UNITED STATES 
The list of special working projects in 
photo-interpretation in forestry made by the 
various forest research stations in this 
country, gives the impression that there must 
be tremendous activity in the various aspects 
of application. This activity can only be 
understood as an increasing appreciation of 
aerial photography in American forestry and 
therefore justified is an assumption that a 
continuation in the development of this im 
portant technique may be expected. 
Although in his previous report Rogers has 
already succeeded in giving an all-round im- 
pression of the various activities, an attempt 
is made herein to give some additional infor- 
mation obtained from the list above men- 
tioned Beginning with applying aerial photo 
stand volume tables, the following recent 
activities can be reported. At the Pacific 
Northwest Forest Experiment Station in 
Portland, Oregon, the work on improving the 
Douglas-fir tables has been continued. Special 
consideration was given to the following ob- 
jectives: 
determination of factors measurable on 
aerial photographs, which are best cor- 
related with stand volume; 
determination of whether a composite table 
will suffice for different conifer species, 
or whether separate tables are needed for 
species groups; 
determination of whether one table will suf- 
fice for all areas in the region, or whether 
separate tables are needed for various 
areas. 
A comparable study is also planned for Pon- 
derosa Pine and associated species, to be 
started as soon as the study on Douglas fir 
has been completed. 
At the Intermountain Forest and Range 
Experiment Station in Ogden, Utah, the 
study to design and test procedures for use of 
aerial stand volume tables in estimating 
volumes on timber sales or other small tracts 
was continued. At the same station a working 
plan was set up to evaluate the relationship 
between field and photo plot sampling proce- 
dures, with special reference to the number of 
field plots required for a given accuracy of 
cruise, to the desirable clustering of field plots 
and to the possibilities of decreasing costs by 
heavier sampling in accessible than in in- 
accessible areas. 
At the Lake States Forest Experiment Sta- 
tion in Minnesota a comparative evaluation 
of different kinds of aerial photography for 
forest surveys in the northern mixed forests 
was made. Objective was: 
determination of the relative usefulness of 
large-scale photography and enlarge- 
ments of small-scale photographs in 
photo-interpretations. 
determination of whether large-scale 
summer infrared or spring panchromatic 
(without foliage) is better for use in 
photo measurements and cover classifi- 
cation; 
determination of whether the use of a Log- 
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