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(633) 
to the highest use and appreciation of those earthly things which God has seen 
fit to give us. 
Much has already been learned about how photo interpretation can help 
us in the inventorying and management of our natural resources. I suspect, 
however, that we have but scratched the surface, and that future Congresses 
will show startling advances beyond those of today. But let us now see where 
we stand. 
What are the techniques used by some of the foremost interpreters? How 
can photos best be used in resource inventories, and what kinds of information 
can be gotten from them? For answers to these questions we will refer to our 
panel of experts. 
Our first speaker will be Mr. Karl E. Moessner of the Central States Forest 
Experiment Station who will speak on Photo Interpretation in Forest Invento- 
ries. 
DISCUSSION OF Mr. MOESSNER'S PAPER. 
Question from Mr. Nash of Canada: “Is a photo scale of 1:20,000 adequate 
for forestry purposes in view of the fact that height can be measured to an 
accuracy of — 10 feet 6796 of the time?" 
Answer by Mr. Moessner: "Probably a larger scale photo would aid in 
recognition of species and in detailed measurements of height, crown, etc. 
However, the correlation between photo volumes estimated on 1:20,000 scale 
and field volumes is very good and I have grave doubts if larger scale photos 
would improve it enough to justify the added cost. In type mapping, bigger 
and better photos are always desired by the interpreter but generally cannot 
be justified on a cost-per-acre basis." 
Comment from Mr. E. W. Jobnson: *Sampling for area is desirable for 
purposes of the National Forest Survey but in private operations a map is 
almost invariably desired. "Therefore maps are made and areas determined 
therefrom. This is true on areas as large as 500,000 to 1,000,000 acres. Such 
maps are used for management and acquisition purposes.” 
Answer by Mr. Moessner: “1 would agree with Mr. Johnson that most 
timber operators need a map of their holdings. But I do not agree that such a 
map is a necessary step in securing a volume estimate. In all except the most 
mountainous areas, the contact prints can be used in lieu of a map by a trained 
interpreter. 
The maps which may be prepared for the operator can then be only 
as detailed as he desires and can afford. Mapping procedures involving 10 to 
40 species, 3 or 4 stand sizes, 3 or 4 sites, and possibly 3 density classes, result 
in hundreds of classifications and extremely complicated maps which often 
are unreadable to all but the men making them. The cost of producing and 
measuring such involved maps is a large part of many timber cruises and to my 
mind can be largely eliminated in the photo procedure. This fact alone may 
allow the aerial estimator to outbid any normal cruising company on most 
cruises. Furthermore, private operators often find it advantageous to complete 
the purchase of a tract in less time than it takes to prepare a detailed map.” 
Question from Mr. Corten of Holland: “One of the requirements for 
inventorization is the measurement of tree heights. What can be done in those