DIGITALNA ARHIVA ŠUMARSKOG LISTA
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ŠUMARSKI LIST 1-2/1972 str. 65     <-- 65 -->        PDF

If we look at the results obtained, we see that the diameter increment
decreases with the reduction of the assimilating surface of the Fir tree. In
healthy Fir trees with their crowns intact the average annual diameter
increment amounted to 3.82 mm., while it dropped to 2.86 mm. in trees
whose assimilating surface was reduced by 10%, and to 2.76 mm. in trees
whose assimilating surface was reduced by 20%, etc. It catches our eye
immediately that the falling-off diameter increment is not linear, because
the reduction of needles by 10% caused a drop of increment by 20%. Regrettably,
in groups of 30%, 40% and 50% we have not a large number of
samples, because in the investigated forest they were not at our disposal
in sufficient amounts. This forest is intensively managed, and thus the trees
that lost more than 20% of their needles are rather rapidly removed. Therefore
these investigations will be continued in those forests where the dying
away of trees spread heavily. Be it as it may, on the basis of performed
investigations it is visible that the reduction of assimilating surface by 10%
caused a reduction of diameter increment not by the same amount, as one
would conclude on first impulse, but by much more. For the purpose of
illustration, I mention here the graph in Fig. 6, which I constructed on the
basis of these investigations. On the axis of abscissas are plotted the assimilating
surfaces of trees, where 1 means the normal assimilating crown, 0.9
means the assimilating crown reduced by 10%, etc., while 0 means the
defoliated (de-needled) trees. On the axis of ordinates are plotted the annual
diameter increments (Zs) in functional dependence on the assimilating surface
expressed in a relative measure.


CONCLUSION


The dying away of Fir forests had as a consequence the falling-off of
increment. In the acidophilous Silver Fir forest community (Abieteto-Blechnetum
Horvat) of »Belevine«, Gorski Kotar (Croatia), it was found out by
measurements that the diameter increment of Fir has been declining in the
1966—1970 time interval. Maximum reduction of this increment was recorded
in 1968 and 1969, after which the increment improved.


This decrease of increment is ascribed to the forest pests — defoliators,
who attacked the Fir forests in masses.


Comparing the diameter increment of healthy Fir trees with that of the
infested ones, it was found that on an average the drop of the increment
in infested trees was about 30%.


The infested trees suffered a definite loss in their amount of needles.
Through these investigations we came to the conclusion that the reduction
of assimilating surface causes the falling-off of diameter increment, which,
for the forest studied, we were able to express by the exponential curve in
Fig. 6, where x = 1 means a full crown; x = 0.9 means the crown lacking
10% of its needles; x = 0.8 means the crown which lost 20% of its needles,
etc., while 0 means a de-needled tree.


From the mentioned curve the following may be seen:


— if the assimilating surface
is reduced by 10% . . . the diameter increment drops by ca 20%
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