DIGITALNA ARHIVA ŠUMARSKOG LISTA
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ŠUMARSKI LIST 1-2/1966 str. 10     <-- 10 -->        PDF

4. Biology of the species and its variability.
5. Inheritance and environment.
6. Selection of trees in plantations.
7. Selection fcr wood quality.
1. INTENSITY (CRITERION) OF SELECTION
The intensity (criterion )of selection can vary. When making a selection
of plus trees of Loblolly Pine (Pinus taeda L.) Peev y (31) classified the
individual characters by points. In order for a tree to be chosen, it had to
achieve a definite minimum of points. According to Prokazi n (32. 33. 34),
the selection of plus trees should be carried out in seed production areas where
previously an inventory was made. Besides other characters, a plus tree should
surpass in diameter b.h. the stand mean tree by over 1.1. According to Mat thew
s (24) evaluation of trees can be performed a) by the descriptive
method, b) by the method of classification, and c) by the method of
measurement. Usually all three methods are combined. The method of measurement
is least affected by the subjectivity of the selectionist and therefore it
should always be applied if possible. Requiring and practising intense
selection is easier if we are concerned with characters which can be
measured, rather than with those which are expressed in a descriptive manner.
The intensity of selection may vary according to selection objectives. If selection
is performed for one or two characters, the selection intensity can be more
severe than if a greater number of characters are under consideration.
Schreine r (36) recommends that selection be restricted to those trees which
exceed the mean by two or three. M e r g e n (25), on the other hand, states
that the selected tree should lei four standard deviations above the mean. If
selection intensity is expressed in this manner, it is impossible to establish
the same criterion for all important characters, because if the intensity is very
severe for some properties as for instance cylindrical term and staightness of
the stem, it will be impossible to select desirable trees.


2. DEVELOPMENT AND USE OF MATHEMATICAL INDICES IN THE
SELECTION OF PLUS TREES
Ander ss on (1) states that selection of plus trees has been performed
so far on the basis of a relative estimate of the growth rate, stem form, saw-
timber grade, wood quality, seed production and resistance. The criteria for
plus trees are changing in different part of the world. They depend on the
species and local conditions as well as the basis of selection. Selection of plus
trees for superior production has sometimes been carried aut on the basis of
estimated indices. Likewise, selection was based on a multitude of characteristics
which were understandably related to the tree quality. Andersson states that
it was possible to use progeny tests as a basis for the selection of plus trees
only to a small extent. He further states that we need selection indices, as
recommended by L u s h, in order to make the selection of trees more effective.
For obtaining such selection indices it is necessary: (1) to have information
about the additive genetic variance and inheritance of each characteristics, and


(2) to test the genetic and phenotypic covariance between these characteristics.
It is possible to achieve all this on the basis of specifically-planned progeny
tests.