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ŠUMARSKI LIST 3-4/1969 str. 8     <-- 8 -->        PDF

used during the previous inventories, because here we were concerned with even-
aged stands. Experiments and calculations demonstrated that in this case it would
be of no use changing the tariff for computation of the current increment in individual
periods between two inventories. Hence I computed the increment on the
basis of tariffs chosen at the beginning of the measurements. Consequently I calculated
the current volume increment for the following time intervals:


1) period 1950—1955 (years: 1951, 1952, 1953, 1954, and 1955);
2) period 1955—1961 (vears: 1956, 1957, 1958, 1959, 1960, and 1961);
3) period 1961—1967 (years: 1962, 1963, 1964, 1965, 1966, and 1967).
The first time interval or control period lasted 5 years, the second and third


6 years each, which totals 17 years from the time I had started these measurements
and investigations.


The calculation of increment was carried out also for the whole time interval
1950—1967 taking into consideration only the first and fourth inventories. This
computation too was performed on the basis of the same tariffs, although for the
calculation of the fourth inventory it would have been convenient to use a little
higher tariff. But as the differences in the results are not significant, I decided to


retain also in thisheight curve« in the stands
case the same
invest
tariffs, becauseigated.
of weak »displacement of the
Results


The results concerning the current annual volume increment are classified in
Table 1- From Table 2 the fluctuation of the annual volume increment of Pedunculate
Oak in the periods investigated may be seen.


Table 2


Period lrst plot 3rd plot 4th plot 6th plot
investigated (Compt. 157) (Compt. 155) (Compt. 155) (Compt. 165)


Years Current annual volume increment, cu.m. per ha


1950—1955 8,4 8,6 10,9 9,3
1955—1961 6,3 8,5 8,9 6,8
1961—1967 4,9 4,2 5,2 5,5
1950—1967 (Average) 6,4 7,0 8,2 7,0


It should be stated that the average value lor the time interval 1950—1967 was
not computed as an arithmetical mean of the measured increments in individual
periods, but was obtained as the difference between the fourht and first inventories.


Discussion


The results obtained show clearly that the current annual volume increment
of Oak stands in the time interval 1961—1967 had dropped by about 50 V« if compared
with the same increment ten years ago.


In order to verify this, I made according to the control method a special
calculation of the diameter increment and came to the same conclusion: The annual
diameter increment in the period 1961—1967, viz. in the last six years, also experienced
a drop of about 50"/» in comparison with the diameter increment in the preceding
period 1950—1967.


For the sake of safety I carried out supplementary tests, so that by means of
increment borer I took increment cores from the neighbouring compartments of
the same management unit. An analysis of these increment cores showed more or
less the same tendency to increment drop.


What is this rapid drop of increment in our best Oako forests to be accounted
for?


Among the various factors which have caused this loss in increment I should
point in the first place to the Gipsy Moth and other insect pests which for quite
a time have been attacking more or less severily these forests, and in association
with certain fungi in definite circumstances have caused the die-back of Oak stands.


Second, I should mention the climatic, edaphic and silvicultural factors which
most probably produced favourable preconditions for various atacks on Oak
forests and thus brought about a serious reduction of the increment.