DIGITALNA ARHIVA ŠUMARSKOG LISTA
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ŠUMARSKI LIST 1-2/1966 str. 15     <-- 15 -->        PDF

to the selection of plus trees which should have been used for seed orchards.
It is certain that in this case caution should be exercised. We consider, however,
that for further improvement also such plus trees can be used.


7. SELECTION FOR WOOD QUALITY
In tree improvement work more and more attention is paid to wood quality,


i.e. anatomical and physical properties of wood. According to Mitchel l (28),
the most important properties are: density, ratio between earlywood and
latewood within the growth ring, number of growth rings per centimeter, fibre
length and thickness, fibril orientation and the occurrence of abnormalities.
Mitchel l (27) considers that these anatomical and physical properties,
especially the position of fibrils and wood density, are genetically controlled.
Zobe l (41) reported in 1954 that specific gravity of the wood of Loblolly
Pine (Pinus taeda L.) is under close genetic control. Later works of Zobe l
and his collaborators on improvement of southern Pines in the U.S.A. strengthened
our knowledge of inheritance of specific gravity. Z o be i (43) says in
general that the length of the tracheids and specific gravity in Conifers are
under genetic control.
Investigations have shown that there are also variations in branching,
growth, stem straightness and other morphological characteristics. Therefore
in the improvement of wood quality it is possible to select individuals with
desired characteristics. Thus, for instance, Du f fiel d (11) reported variation
in trachcid lenght in Pseudotsuga menziesii (Mirb.) Franco. Similar types were
found among trees within the same stand. By means of a graphical method
it was possible to estimate the extreme plus and minus variants. Va n
B u i j t e n e n (5) found significant differences in wood density among clones
of Loblolly pine (Pinus taeda L.). He also found differences in wood density
in progenies originated from controlled pollinations. According to Mitchell (28),
the well-established ratio between wood density and pulp content provides a
method of evaluating trees on the basis of wood density. Trees can be classified
as below average, average, above average or outstanding with respect to wood
quality. We believe that in the improvement of wood quality the mathematical
indices will be determined first, for use in the selection of plus trees. Substantial
progress has already been made toward achievement of this objective.


SELEKCIJA PLUS STABALA


UVOD


Plus stabla koriste sc, ´kako navodi Schreine r (36), za podizanje sjemenskih
plantaža, za uzgoj ukoliko je moguće klonsko razmnažanje putem rožnica te za korišćenje
kod hibridizacije, tj. rada na oplemenjivanju. Prema tome razumljivo je da
se velika pažnja pridaje izboru plus stabala. Od izbora početnog materijala u mnogome
ovisi i uspjeh daljnjeg rada na oplemenjivanju kao i konačni rezultat. Razvojem
šumarske genetike razvijale su se i metode izbora plus stabala. U početnim
stadijima šumarske genetike kada se radilo s velikim entuzijazmom, ali možda s manje
znanja o nasljeđivanju svojstava kod šumskog drveća, izbor plus stabala vršio
se uglavnom okularnom procjenom. Smatralo se da takav izbor u potpunosti zadovoljava
i da će daljnje korišćenje tako izabranog materijala sigurno dati željene re