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32 Yrjö Ilvessalo, The Forest .’Resources’ of Finland in 1936—1938
Table 18 illustrates the division of the total volume of the different
species into diameter classes. As already mentioned, the total volume
of pine has decreased materially. It is now evident that this reduction
has occurred principally in the growing stock of pine of large size. In
North Finland, however, the growing stock of pine of large size has
only decreased slightly, the volume of pines of a diameter of 30+ cm
even remaining unchanged there. The total volume of spruce has
already been shown to have increased. The increase refers to spruce
of a breast-height diameter below 20 cm, while the growing stock of
spruce of large size has decreased slightly, relatively most in North
Finland. The figures for the volume of birch record a falling off as
regards trees of large size (20+ cm) and the smallest trees (<10 cm),
but shows that the 10—20 cm diameter class has increased. Taking
into account the correction of the former volume of birch (in 1922—23)
already referred to, the decrease in trees of large size is reduced to
about 6 million m3 and the increase in the 10—20 cm class is raised
to about 19 million m3.
4. Quantity and quality of wood suitable for the sawmill and plywood industry.
Special attention was paid in the survey to trees of large size, i.e.
to wood that was suitable for the sawmill and plywood industry.
These consisted of coniferous trees that yielded a log of at least the
size of 18’ X 6" and such deciduous trees as were estimated to yield
a log of not less than 18’ X 7" (in exceptional cases down to 14’ x 7"
or 12’ X 8"). From the quantity of trees of large size, therefore, all
such trees were omitted as corresponded to these minimum
measurements, but, owing to some defect, did not yield a log of at least the
size mentioned. Table 19 gives the total quantity of these trees of
large size and their average number per hectare on productive forest
land and the total forest area. Aspen and alder of large size, which
are very few in number, have been combined with birch.
The total number of such trees of large size is 1 175.0 million and
their average number per hectare is 47.3 on the total forest area and
58.5 on productive forest land. Only 29.4 million trees of the total
grow on poor productive forest land. If the minimum diameter at a
height of 18 ft were fixed at 5", as is frequently done, the quantity would
be increased by several hundred million. Relatively the greatest
number of trees of large size grow in the waterway regions of West
Finland (74.2 and 65.6 per ha), in which the growing stock is also
richest in other respects, as already demonstrated. West Finland is
followed at a considerable distance by East Finland, then by North
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