DIGITALNA ARHIVA ŠUMARSKOG LISTA
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ŠUMARSKI LIST 3-4/1969 str. 7     <-- 7 -->        PDF

DIMINUTION OF INCREMENT IN OUR VALUABLE OAK FORESTS


by Prof. Dr Dušan Klepac, Zagreb


When after a two-year stay in Mexico I returned home early in 1968 and
inspected again the experimental plots of the Chair for Forest Management situated
in the lowland forests of the Sava River area, management unit »Josip Kozarac«, I
was in for a surprise. Even before the Slavonian forest had flushed, it seemed to
me at first sight somewhat less vigorous than before. I at once thought it might
suffer from a disease. On inspecting individual plots in more detail, however, I
noticed that the bark on numerous Oak trees was swollen up and assuming a
specific appearance in places. This was mainly manifest in the lower parts of the
stem where I was able to remove with the fingers the normally hard Oak bark.
Beneath the bark I noticed that the wood was blackened, and that the mycelia
were visible in places. I may say that in middle-aged and even oldest mixed Oak
stands nearly every third or fourth Oak tree was attacked in this manner. I had
noticed this on several occasions in the spring of 1968 in mixed Oak stands with
Hornbeam which were considered biologically resistant, and which were exceptionally
well formed, valuable and highly productive. It was exactly in these stands
that a few years ago I determined high current volume increments of about lOcu.m.
per ha./year. These data were repeatedly verified and accepted as such. True,
already in previous years 1 had established reductions of current volume increment
owing to attacks by the Gipsy Moth (Lymantria dispar L.) or by other insect pests
such as the Oak Leaf Wasp (Apethymus abdominalis Lep.), the Pine Processionary
Moth (Thaumetopoea processionea L.), the Oak Leafroller Moth (Tortrix viridana
L.), etc.* On the same occasion it seemed to me very interesting and important to
measure again the increment of the mentioned stands, for already at first sight I
had noted that their vitality was weakened. I was prompted to this even more by
the fact that my colleagues at the Faculty had already undertaken steps to control
the die-back of our Oak forests, having noticed this phenomenon much earlier
than I. Bearing this in mind, I will limit myself here to the measurement and
determination of the losses caused by the die-back of Oak forests. In this connecttion
I made up my mind to carry out a fourth inventory of the oldest experimental
plots. They were: the first (compt. 157), third (compt. 155), fourth (compt. 155)
and sixth experimental plots (compt. 165) in the management unit »Josip Kozarac«,
forest district of Lipovljani (Croatia). Accordingly, I wanted to determine by exact
methods toda´s growth rates of these same stands which — until recently — had
ranked among the most productive and well-formed lowland Oak forests.


Work method


The work method consisted in the remeasurement of breast height girths of
trees by means of a steel girthing tape in the same manner as done by myself
during the first and second inventories in association with Prof. Dr M. Plavsic, and
the third inventory in association with ing. R. Križanec. In fact, last spring I performed
a fourth inventory marked as inventory 1967. The first inventory was done
in the spring of 1951 (inventory 1950), the second in the autumn of 1955 (inventory
1955), the third in the spring of 1962 (inventory 1961).


Considering that stems on the experimental plots are marked numerically, and
that ing. R. Križanec and myself had by turns measured each experimental plot
twice, rough errors were eliminated and the systematic errors were reduced to a
minimum.


The calculation of increment was made according to the control method in
the manner described in my book »Rast i prirast šumskih vrsta drveća i sastojina«
(Growth and Increment of Forest Tree Species and Stands, Zagreb, 1963, pp. 199—
222, with the remark that in this book one of the mentioned experimental plots
(the 4th experimental plot, compt. 155) was taken as a model. This time, however,
in addition to the volume increment I also measured and computed the diameter
increment according to the control method. When calculating the volume increment
there arose the question whether it was necessary to change the tariffs which I had


* D. Klepac: Zuwachsverluste in Eichenmischbeständen, die durch die Kalamität des Schwammspinners
und anderer blattfressender Schädlinge befallen wurden. Wiss. Z. Techn. Universität, Dresden,
15 (1966), Heft 2. (A report held on the International Symposium on Increment at Tharandt, October,
1965).
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