DIGITALNA ARHIVA ŠUMARSKOG LISTA
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ŠUMARSKI LIST 1-2/1966 str. 12     <-- 12 -->        PDF

characters are not genetically interrelated (Me r ge n 25). Moreover, it is very
difficult to find a tree which is excellent in many characters. If on the other
hand, we lower the criterion, i.e. the intensity of selection, we cannot expect
any greater improvement in desired characters in the subsequent generation.
Trees are now more and more selected with regard to one or two characters.
Thus we have, for instance, quality-plus trees, volume-plus trees, trees selected
with regard to the technical properties of wood, plus trees selected as resistant
to diseases, insects or non-biotic factors (frost, drought, etc.).


Investigations carried out so far have proved that in forest tree species a
number of characters are genetically bound, i.e. that a correlation exists between
them. For instance, Kiellande r (19) established a correlation in spruce
between bud formation and resistance to spring frosts. K i r s t (20) found that
a correlation exists in Beech between bark shape and wood properties.
L a n g n e r and Ster n (22) found a correlation in spruce between time of
bud bursting on the one hand and height growth and latewood formation on
the other. Hois t (16) found a correlation in Norway spruce between size of
crown and resistance to weevil. Fieldin g (13) found in Monterey Pine (Pinus
radiata) a correlation between the number of whorls in branches which are
formed annually and the abundance of fruiting, and between the lenght and
thickness of branches on the one hand and bole straightness on the other.
Heimburge r (14) considers that degree of facultative parasite attack is
often negative by correlated with host vigor. Therefore the author recommends
that in selection we should aim at those individuals which exhibit an above-
average growth rate on an average quality site. The results achieved by
Ehren berg, Gustafsso n, Plym For shell, and by Si mak (12)
are important. They established that minus trees of Scots Pine have larger
cones than plus trees. Also, form, weight and number of seeds change with
change in cone shape. Although minus trees have heavier seeds and thus a
higher juvenile growth rate, the minus-tree progenies later fall behind in growth,
often by the third year. The authors consider that these as well as other
characters are caused by semidominant or semirecessive factors.


On the basis of the above information concerning the correlation of
characters we can conclude — as stated also by Ma 11 h e w s (24) — that in
selection of plus trees it is necessary to take into account correlation between
individual characteristics.


However, it is specially important to establish a correlation between the
parents and the progeny. Nil s s o n (29) established in Norway Spruce and
in Scots Pine that there exists a clear correlation between the ratio
height/diameter b.h. (H/D) of mother trees and the average height of the
10-year-old progeny. No correlation was found between the volume of mother
trees at constant form and the average height of the progeny. Therefore the
author recomended to select higher trees with equal diameter compared with
the greatest neighbour trees, as mother trees for crossing experiments and seed
orchards.


4. BIOLOGY OF THE SPECIES AND ITS VARIABILITY
In the selection of plus trees it is important to be well acquainted with
the biology of the individual species. Knowledge of local races and ecotypes
will greatly facilitate selection of the most suitable trees for further improvement