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ŠUMARSKI LIST 1-2/2018 str. 53     <-- 53 -->        PDF

In Kukavica virgin forest, seven sample plots were established. Therefore, when calculating the mean and standard deviation of the observed characteristics (volume, biomass, carbon) in a sample of all sample plots (n = 7, xi-size of the observed characteristics per hectare) weights were used. Weights are surface plots (pi). The arithmetic mean was obtained by formula (8), and the variance by formula (9).
                                (8)
                                (9)
To test the statistical significance of the differences in the proportions, arithmetic means and the variance of the observed characteristics of the managed and virgin beech forests Z and F test were used. Z test was used to test the null hypothesis about the equality of proportions and arithmetic means, while F test was used to determine the differences between the variances. Two large and independent samples were used for the testing. From the statistical point of view, the problem was that the study sample plots were not always of the same size. The managed beech forest plots were 0.05 ha in size and there was a total of n1 = 127. Kukavica virgin forest had sample plots of 0.15 ha to 0.79 ha in size and there were seven of them. In Danilova kosa and Vinatovača virgin forests, a total survey was conducted, so it was assumed that each ha was a plot (totally 35 ha). Thus, the size of the second sample was n2 = 42.
In order to facilitate statistical analysis, the data from all sample plots established in the managed forest and in Kukavica virgin forest were converted into hectares. So this conditional hectare was equated with an actual hectare in the virgin forests of Danilova kosa and Vinatovača. Thus, hectare was used as the basic unit of observation in both samples. The number of ha in the stand was used as the weight (frequency).
Stand quadratic mean diameter (Dg) and Lorey’s mean height (HL) were calculated for all stands.
RESULTS AND DISCUSSION
REZULTATI I RASPRAVA
Height curves – Visinske krivulje
Height curves show certain differences in the shape of curves and in the heights of thin trees (diameter of 10 to 30 cm) in the managed (Fig. 2) and virgin forest stands (Fig. 3) in Serbia.
The shape of height curves is different in the diameter of 30 cm because the slope of the curve is higher in the virgin forest stands than in the managed stands. The height of medium-thick and thick trees is nearly uniform.  Comparing height curves in Uholka virgin forest in Ukraine and managed uneven-aged beech forest Sihlwald in Switzerland, Commarmot et al. (2005) found no significant differences in the relation of height to diameter at breast height in diameters from 8 to 86 cm (maximum diameter of beech in Sihlwald). They also observed that height curves had a similar shape.
Comparing Figures 2 and 3 we can conclude that thinner trees in the virgin stands attain 3.4 m (diameter 15 cm) and 1.8 m (diameter 25 cm) lower heights, while the average difference in the height of medium-thick and thick trees (diameter from 30 to 100 cm) is + / - 0.5 m.
Structural diversity – Strukturna raznolikost
The diameter distribution of the managed stands (Fig. 4) can roughly be identified as the distribution characteristic for selective managed stands. Diameter distribution of the virgin stands Danilova kosa and Vinatovača can be roughly described as the virgin forest stand structure (Fig. 5). The largest number of trees are in the diameter classes of 10 to 25 cm and 50 to 80 cm. Similar results in the study of diameter distribution of virgin forest stands in Eastern, Central and Southern Europe were obtained by other authors (Meyer et al. 2003, Commarmot et al. 2005, Drössler & Lüpke 2007, Bilek et al. 2011, Kucbel et al. 2012). Partially different shape of