leciduous trees by 
yurpeses, however, 
tographs. It is still 
y, but experiments 
being made. 
the south and west 
wood stands. 
rometer and paral- 
ng. 
their shadows on a 
irement of parallax. 
1 volume was made 
ni 3° at the E.I.R.A. 
scale of the plotting 
4x. In the plotting 
executed according 
'oniferous trees the 
d for forests of Me- 
ge value of the dif- 
g were determined, and 
ly drawn in the plotting 
:nown formulae, using a 
und. 
11 parts within one hec- 
» was discovered by Dr. 
in a stereoscope of an 
| a complete plotting of 
'erences of the trees are 
25 
The trees are then grouped on the basis of their size (area — height), and the volume 
of the different groups are calculated by the aid of a special reduction coefficient, de- 
termined for the proportional boundaires of the relation mentioned above. 
The accuracy of these determinations of volume amounts to € 5 per cent in relation 
to the results gained by measurements on the ground. 
When surveying the heights of the deciduous trees, variations of X 35 cm were ob- 
tained, while variations of = 0.250 m2? were obtained at the determination of the average 
area. The result is considered as very satisfactory for an accurate determination of 
volume by statistical reduction coefficients. 
Finally, the ultimate plan of the small parts are drawn on to a photo-map, scale 
1:10.000, to get a general survey of the real condition of the forest. Different colours 
are used for this. 
The average cost per hectare is 1.300 Italian lire, including mapping and measurement 
of the trees. It is reckoned that for maps of more than 30.000 hectares, the cost can 
be limited to 900 Italian lire per hectare (flight included). These prices are very ad- 
vantageous, considering that a topographic map alone of the forest, compiled on the 
ground, with regard to the details of the terrain may cost 500 Italian lire per hectare, 
while the map for height determination of trees, made on the ground, comes to 3.500 lire 
per hectare. 
One must not forget that oblique pictures are of great help to tree- 
measuring, as they often — in bare parts of the forest — give a glimpse of 
the tree from base to top, thus making it easier to find out the reduction 
coefficient for the determination of volume in question. 
Sweden: 
Height of trees and stands has been measured in various stereo-instru- 
ments. For the most part reflecting stereoscopes with micrometers have 
been used. Usually the height has been underestimated by between 1 and 
2 meters (negative scale 1 : 15000 and larger). The reason for this is thought 
to be that the slender tops of the tree crowns cannot be seen in the stereo- 
photographs. It is furthermore often hard to see the ground between the 
trees because of shadow, ground vegetation and boughs. Height measure- 
ments calculated from the length of shadow give a similar result. Photo- 
graphs of higher quality are needed. 
U. S. A.: 
The parallax bar is about 4 to 5 times as consistent as the parallax wedge 
and costs about 30 times as much. 
Question No. 5: 
Determination of timber volume (trees, stand, forests). Here should be 
mentioned on one hand, what purpose the volume measurement serves (forest 
management, estimation of cutting areas, taxation), on the other, what part 
of the tree is counted in the timber volume. Observations concerning the 
measurement of the diameter of the tree crown is of special interest. 
Finland: 
In 1949 there was made, under the direction of Eng.Lt.Col.Lófstróm, 
an examination of the possibilities of estimating the volume on aerial pho- 
tographs. In a publication » The Use of Air Photographs in Finnish Forestry», 
issued in connection with the third World Forestry Congress 1949, a short