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ŠUMARSKI LIST 1-2/1966 str. 76     <-- 76 -->        PDF

because (1) the performances expected at older ages are still not known, (2)
inferior individuals have not yet been rogued and they contribute inferior
genes to the population. However, in the case of gene preservation plantations,
these points do not apply. Here the objective is to collect seeds from the
registered plantations with the minimum loss of genes. Therefore, the seeds
should be collected as soon as the stands reach full sexual maturity.

Besides the four major conifers, we have several tree species which are
harvested in natural forests and are desired in the market but are not planted.
Some of them supply rather large quantities of timber, such as Abies firma,
Tsuga sieboldii, Castanopsis cuspidata, and Machilus thunbergii. Others, such
as Sciadopitis verticillata, Torreya nucifera, Betula grossa, Quercus gilva,
Zelkova serrata, Cercidiphyllum japonicum, Cinnamomum camphora, and
Fraxinus sieboldiana, are rather scarce but produce timber of good quality.
Natural stands usually show much smaller increments of standing crops than
artificial plantations, so they are being rapidly replaced with the latter.
Although there are still fairly large stands of naturally regenerated second
growth, it is quite seldom that superior specimens of these species are able
to establish their offspring. Because of this, the preservation of the gene pool
is urgently needed. In fact, it is already too late for some species such as
T°rreya nucifera, of which almost all of larger specimen has been felled

For those species such as Abies firma or Castanopsis cuspidata which appear
more commonly in the form of almost pure stand, the same method of
sampling as for planted stands can be employed. For the species of rare
occurrence, it is necessary to select a sufficient number of seed trees throughout
a wider region in order to avoid considerable inbreeding.

It is well known that an isolated group of a few individuals have a high
degree of inbreeding, which increases generation by generation, until little
genetic variation is shown within the group (Sewall Wright efect). In such
cases, only a small area is needed for the preservation of each small population,
but the desirable procedure is to obtain wide genetic variation by mixing
several populations into a single plantation.

The species which are not often planted are usually slow-growers and
require large dimensions for their commercial maturity. Therefore, they have
to be retained far longer than the usually planted conifers.Such slow growth
is the main reason why these valuable species have not been artificially
propagated, and it makes it difficult, at the same time, to get an area of forest
land to plant the seedlings for gene preservation. In the authors opinion, the
best place to grow them is on the protection belts which separate commercial
plantations and consist of natural vegetations. The belt is used as a safeguard
of the plantation against fire or pests and, in total, amounts to very large
areas. It is, therefore, favorable not only from the genetic point of view but
also from the commercial one that the seedlings of these valuable species are
planted mixed with natural second growth, because the operation will give
increased quality products.

Unfortunately, we have not yet been able to start such a program, but
there are good prospects to do so soon.

Finally, we have to discuss the analysis of the genetic variation of the
populations. From the view point of gene preservation only, it is not necessary
to distinguish seeds from individual seed trees, but it is not difficult to collect