9 
depends on many other conditions. Naturally it is very difficult to con- 
sider and measure all these conditions. In some site classification 
systems therefore forest types and indicator plants are used to charac- 
terize site. In most cases however the trees themselves are used for this 
purpose. For practical reasons it has been necessary to use a very little 
number of independent variables ,usually only two, tree height and 
tree age. 
The site quality which is determined with the use of special height- 
age-tables, is the ideal one, or the mean production, which will be gained 
from carefully thinned sample plots with a good stand density, and 
where all wood is taken charge of. In practice however the ideal pro- 
duction, expressed in cubicmetre per hectare and year, is reduced about 
15—20 96 according to special formulas. 
[n aerial photographs there are only a limited number of variables 
to be used. They are the height of trees and stands, crown diameter, 
crown closure, the number of thee crowns, tree species and forest- 
type. Some of them can be measured but other only estimated. It is 
also possible to study topography in aerial photographs and from it 
conclude on geology, soil condition, local climate, the condition of nut- 
riment, moisture, heat and blocks of stone. The area of the sections can 
be measured on maps, which have been compiled photogrammetrically 
or geodetically. 
Site quality therefore must be determined in three steps in the same 
way as the mapping out and also at the same time as and in connection 
with that work. (Compare 2.2) 
3.2. The primary material of the investigation 1s collected from some 
very large reallotments in Dalecarlia. The number of sample plots is 
115, 72 of them with scots-pine stands, 5 for the main part with pine 
stands, 14 with pure Norway-spruce, 2 for the main part with Norway- 
spruce, and 22 with one half pine and one half Norway-spruce. The 
number of measured trees within 95 sample plots is 8—12 and within 
20 plots 4—6. The results of measurement consequently are given the 
weights of 1 respectively 1/2. The area of a sample plot usually is 0.1 
hectare (25 X 40 metres). 
For each sample plot were determined soil type, forest type, tree 
species, tree height, stem diameter at brest height, crown diameter, 
crown closure and site quality. 
The aerial photographs used are for the main part taken in 1950 (at 
the negative scales of 1:8 400 and 1:16 500), some of them already in 
1947 (at the negative scale of 1:5 200) all of them with the aerial ca- 
mera Zeiss Topogon 20/30 and panchromatic film. l'or the area accoun 
ted of in 2.3 the photographs are taken with Wild RC 5 at the scales 
of 1:8 000, 1:13 000 and 1:18 000. 
The primary material, accounted of in 2.3 is also used, for a preli