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ŠUMARSKI LIST 1-2/1966 str. 63     <-- 63 -->        PDF

and the practical foresters´ knowledge of forests (Schreine r 1950). After
summing up the data of investigations on the variability of populations, one
must select:

(1) the representatives of geographic races;
(2) the representatives of ecologic races.
The best representatives of these races should be selected by their genetically
related and economically important characters.
If the available data do not offer a satisfactory insight into the existence
of races and their separation, we should select:

(1) the best populations and individuals grown in normal sites for this
(2) the best populations and individuals grown under the conditions of
ecological extremes.
In practice, one must usually combine choice of representatives of known
races with selection of representatives on the basis of forest inventory data.
Wrigh t (27) is of the opinion that different geographic races are formed
at distances greater than 200 km and that local, ecologic races arise in site
extremes and under conditions of isolation. Further studies of the natural forest
resources will yield better knowledge of races, as well as completing the
selection of material. Valuable data will also be obtained from studies of
earlier selections.

Discussion about the problem how to select should be conducted in two

(1) to determine the number of population samples to select within a
(2) to determine the number of genotypes to select within a population.
The number of population samples of a species which will be selected for
preservation as the gene pool of natural forests of the species depends on the
genetic differentiation of populations, i.e. on the existence of races and their
number. The genetic diferentiation of the populations of a species depends on
the size of the area of distribution (in the geographical and altitudinal sense),
the uniformity or variability of its sites, and the spatial isolation of the habitat.
The greater the area of distribution, the more varied will be the sites. The
greater the intermediate range of individual growing areas, the greater will
be the genetic differentiation of populations, and, of course, the greater will
be the number of necessary samples of the gene pool to be preserved. This
general rule can also serve as a guide when deciding how many population
samples are needed for those species whose races have not yet been thoroughly

Theoretically, it is necessary to preserve samples of the genetic material
of all races of a species. Practically, the limits will be set at the outset by
economic considerations. In any case, choice should begin with the most
characteristic and significant populations. Then it should gradually go more
deeply into details.

The problem of the number of genotypes of a population to select in
order to preserve to a satisfactory extent its gene pool is of particular concern.
We have already discussed one aspect of this problem: considering the
heterozygous character of most genotypes of forest tree populations, we may
conclude that the variability of the gene pool to be selected is may times
greater than the number of selected genotypes, and that the genetic material