Joint International Conference on Long-term Experiments ...

ms. The placement of the areas was selected in such a way so as to render the structure
of the stand as accurately as possible.
Within each area the diameters of all the trees from different species were
measured and also the heights of the trees at the medium central diameter, for each
particular species. After collecting the data from the field, the structure of the stand, for
every species and diameter categories were discussed. With the help of the data, the
structure of the stands was evaluated according to the diameter categories, using
distributions recommended by specialists in this field: Gauss distribution, A type
Charlier distribution and Beta distribution (Giurgiu V., 1979, Giurgiu V., 1972).
Hi-square criterium was applied to assess the quality of the adjustments on the
experimental distribution, after the theoretical ones. After the structure of the stands was
revealed, there was a simulation of some breaks(thinnings), through which it was
intended to promote the most valuable pieces of stand, in what species and quality were
concerned, to improve the quantitative production and especially the qualitative
one(Florescu I., Nicolescu N., 1998).
The simulation of a break has been accomplished relying on the data from the
field and also by using data, obtained on the basis of the adjustment of experimental
distributions with those recommended by the specialists. The quality of the simulated
break was verified by calculating the dispersion indicators, the indicators of the form of
the distribution, the intensity of the breaks connected to the number of trees, the basic
area and the volume, Hart-Becking index (spacing factor) before and after the break.
The volume was calculated with the help of the relative volume method, a method
which is recommended by the specialised literature.
The structural differentiation in a stand is a consequence of the integrality state and
leads, eventually, to the self-thinning of the trees, following the self-improvement trait
of the biological systems.
3. RESULTS AND DISCUSSIONS
To describe the simulation and the evaluation of a break in a stand, some synthetical
data is presented in the following lines, data which has been calculated before and after
the simulated break in a.u. 78C U.P.III, F.D. Dobreşti.
Table no. 1 The calculating of the medium diameter, dispersion indicators and of the
distribution form case 1
Calculated characteristics Before the break After the break
Medium diameter(cm) 22,04188482 26
Variance 67,44612783 65,92
Standard – Deviation 8,212559152 8,1191133
Variation factor 0,372588788 0,3122736
Asimetry -0,142394868 -0,9295828
Excess 1,89798843 2,5502924
From the above data one can notice that the simulated break consisted of the extraction
of the trees from the inferior diameter categories, mostly white beech trees, but also
503