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PENNIA 66, N:o 5
41
1 million m3 in consequence of a reduction in the growing stock and
of the comparatively abundant young forests in some districts having
grown older. On a similar examination the growth of the forests in
Ostrobothnia is approximately the same as in 1922—23, although the
area of productive forest land has been reduced by about 100 000 ha.
Investigations made in connection with the survey into the
periodicity of the growth of trees lend fresh support to the
view, previously confirmed, that periods above or below the average
occur in the growth of trees and consequently of forests. As far as
these investigations have proceeded, this has proved to be the case
especially in regard to the growth of pine in the southern half of
Finland. It is evident that especially in the surveys made in the 1920’s,
i.e. also in the first National Survey of the forests of Finland, the
investigation of the growth at least in the respect just mentioned
resulted in a periodicity of growth above the average and in the present
survey in an average periodicity of growth or one slightly below the
average. According to this the survey in 1922—23 may have given
too favourable an idea, at any rate as regards the growth of pine in
the southern half of Finland, and the present survey in the best case
an idea corresponding to the average. This ought to be kept in mind
when examining later on the changes in the growth of pine. The
conclusions to be drawn from this must, however, be postponed until
this aspect has been fully investigated on the basis of the rich
materials gathered in the survey.
The division of the total annual growth according to the different
species of trees will be seen in Table 24, in which the results
of the survey in 1922—23 are included for the sake of comparison.
Although the same factors interfere with a comparison as in the case
of the growing stock as well as the variation due to the difference in
the method of calculating the growth, the trend can be described
approximately, taking all these circumstances into consideration.
The growth of pine, according to Table 24, is now nearly
1 million m3 less than in 1922—23, and if the difference due to the
methods of calculation is taken into account, the actual reduction
may be estimated at about 1.9 million m3. In North Finland the
growth of pine has increased according to the table by about 1 million
m3 and, even if the same method of calculation is employed, by 0.7—
0.8 million m3. The decrease in the growth of pine therefore refers
entirely to the southern half of Finland, amounting according to the
table to 1.75 million m3 and in reality to about 2.6 million m3. The
reduction is largest — according to the table 1.06 and in reality about
1.5 million m3 —in East Finland, while in West Finland it is below
2
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