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ŠUMARSKI LIST 1-2/2019 str. 49     <-- 49 -->        PDF

basal area was removed from the stand by applying three different selective thinning intensities of 0% (control), 18.9% (moderate) and 28.2% (heavy). The trees selected for thinning in each plot were then marked, felled and removed from the stand (Çiçek et al., 2010).
In November 2012, the d1.30 of each numbered standing tree in the experimental plots was re-measured with precision calipers. The seven-year diameter increments of the plot were determined by subtracting the 2005 plot diameter averages (of the remaining stands) from the 2012 diameter averages. Three sample trees were selected from each plot for a total of 27 trees. Of the three sample trees selected in each parcel, two represented the co-dominant trees and one represented the dominant tree. The selected sample trees, having normal stem and crown shapes, represented the seven-year diameter increase in their class for that plot.
After the northern sides of the selected sample trees were marked, they were felled and their height was measured. After the branches on the stem were removed, 4-5-cm thick disk samples were taken from different sectional heights (0.30 m, 1.30 m, 3.30 m, 5.30 m, ..., and 21.30). The base diameters of the sample trees (soil level) and the number of annual rings in the bottom log were also recorded. Later, the cross-section disks representing the sample tree were placed separately in air-permeable sacks and transported to the laboratory. The sections were procured and measured for stem analysis according to the published works of Kalıpsız (1999) and Giray (1984).
In the laboratory, without allowing the sections to dry, a line was drawn across the diameter of the upper surface of each cross-section bisecting the core in the north-south direction. In addition, a diameter line was drawn in the east-west direction passing through the center perpendicular to the north-south diameter. All the rings of each section were counted and registered in the stem analysis form. Seven annual rings were then counted in each direction, from the outside to the inside, and the annual ring corresponding to this age was marked, indicating that the ring represented the radius of the tree without bark in 2005. The 2005 diameters without bark and the 2012 diameters with and without bark were measured on each section within an accuracy of 0.5 mm. With the help of these measured diameters, the diameters without bark in 2005 and with and without bark in 2012 were calculated for each section. Thus, the relationship between the diameter without bark and the double-bark thickness was derived by using the values of the bark-free diameters of 2012 and the double-bark thickness values corresponding to these diameters (R2 = 0.738), as in Equation (1).
                k = 0.0012 d2 + 0.3456d + 1.2375                          (1)
where k is the thickness of the bark (mm) and d is the sample diameter without bark (cm).
In each sample tree, the diameter over bark of 2005 was subtracted from the diameter inside the bark of 2012, and the seven-year diameter increment of each section was calculated. In the sample trees, the arithmetic mean of the diameters of all sections was taken and the average stem diameters (2005 and 2012) and stem diameter increments for each sample tree were determined. In addition, the percentage of diameter increment was calculated as the ratio of the seven-year diameter increment to the diameter of the year 2005.
Statistical analyses – Statistička analiza
First, the obtained data were subjected to variance analysis (ANOVA) to determine the effect of thinning intensity on the d1,30 growth and increments of the sample trees. Variance analysis was then carried out to determine the effect of thinning intensity, cross-section height and thinning intensity × cross-section interaction on the diameters, diameter increments and percent of diameter increments of the sample trees (dominant and co-dominant) at different section heights. Analyses were performed separately for the dominant and the co-dominant trees. When the ANOVA results were found to be significant, the Duncan test was used to compare the averages. In evaluating the data, the SPSS (version 21) package statistical software was used and the results were regarded as statistically different at a level of p <0.05. Before the analyses, it was confirmed that the data of all variables exhibited a normal distribution and the variances were homogeneous.
After the thinning, the mean d1.30 was similar in terms of treatments (p >0.05; Table 1) for the co-dominant and dominant trees in the remaining stand (23.6 and 27.8 cm, respectively). Seven years later, the d1.30 of the dominant trees in all plots showed a similarity and the d1.30 of the co-dominant trees for the moderate and heavy treatments were similar, while being 12% greater than the control (Table 1).
The d1.30 increments of the co-dominant trees were similar in the thinned plots and greater than the control (p <0.05). When each treatment plot was evaluated within itself and compared to the remaining plots after the thinning, the d1.30 increment of the co-dominant trees had increased by 16% in the control plots and 22% in the thinned plots. Compared to the control treatments, the d1.30 of the co-dominant trees in the thinned plots had increased their diameter by 43% (Table 1). The d1.30 increments for the control and moderate treatments of the dominant trees were similar to each other and were lower than for the heavy treatment (p <0.05). The d1.30 diameter increment in the heavy treatment plot was approximately 20% higher than in the other treatments plots. Moreover, when each treatment was compared within itself, the d1.30 diameter increments were greater in the dominant trees than in the co-dominant trees (Table 1).