DIGITALNA ARHIVA ŠUMARSKOG LISTA
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ŠUMARSKI LIST 1-2/1966 str. 13     <-- 13 -->        PDF

work and establishment of seed orchards, or for immediate use for silvicultural
purposes. Norway spruce and Scots pine are examples, with their high and low
elevation races, as is the Norway spruce ecotype occurring in frost localities.
In plus-tree selection, attention should also be paid to phenology B o 11 a n d (2).
For instance, the length of the growing period is an important factor. In beech,
according to Hoffman n (15), there are differences in time of flushing
within provenances and between provenances. It is also very important to
know the range of variability of characters to which we pay special attention
in the selection of plus trees. A determination of the range of variability will
enable us to approach more safely the selection of plus trees. For the purpose
of illustrating this, D o r m a n (9) demonstrated that the distribution curves
of height, diameter b.h. and basal areas of two evenaged stands of Slash Pine
(Pinus elliottii Engelm) are different. 2 u f a (44) has established for stem
straightness of Black poplar from the middle Danubian lowlands that the
range of variability of this character is not the same in all investigated
populations. He also found that the magnitude of variation of this property
is to a large extent genetically conditioned. In contrast, Campbel l (7)
established in Douglas fir that its branching or crown habit is to a very small
extent an inherited character in a broad sense, which points to the fact that
the selection of plus trees for this character is futile.


It is well-known that tree habit varies with age. Therefore this should also
be taken into consideration in plus-tree selection. Because in younger coniferous
trees the micrcecological factors influence their habit, Bouvare l (3)
recommends that in fast growing conifers, one select plus trees among specimens
which have reached or passed their normal age of maturity. In Norway spruce
this would be 100—120 years, and in Douglas Fir over 50 years. Matthew s
and McLea n (23) stated that in selection of plus trees of Scots pine, difficulty
arises from the variation in external appearance of the tree with age and
growth conditions. Mitchel l (26) reported that variability in tree habit of
European Larch at different ages leads to a new problem in tree selection. A
50-year-old tree should have an excellent habit, height and diameter increment.
At the age of 100—120 years such a tree changes its shape, but in spite of this
the decisive factors in selection at this age are large height and diameter
increments, and the quality of the stem. Trees of European larch between 100
and 150 years of age are selected on the basis of bole quality, diameter and
length, which in this case is more important than the total height.


We consider that for the present it is difficult to give a final statement
as to how old an individual should be for selection as plus tree. Both upper
and lower age limits should be neither too high nor too low. At the same time
it is important to know the variabitily of habit of trees in relation to age, as
described by Mitchell for larch.


Just because of this variability in a species we consider it nesessary to
select a great number of plus trees. Only in this manner will it be possible to
cover the variability of a character and reduce risks in further improvement,
as stated by Stern (37).


The work of Open s ha w (30) is very interesting from the standpoint of
improvement. After classifying 140-year-old Scots pine trees into 11 types
according to habit he observed that types with horizontal branches (especially
the broadcrowned ones) have the best volume characteristics from a utilization