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ŠUMARSKI LIST 3-4/2019 str. 69     <-- 69 -->        PDF

the middle of the distance between the trees on the edge of the stand that belong to it and the neighbouring trees outside the stand. Based on the coordinates of every individual tree in the space defined in the previously mentioned way, the so called ’’Voronoi’’ polygons were constructed (Okabe et al., 2000) which were used to present the growing space of the trees in the stand above ground. ’’Voronoi’’ polygons were defined using the deldir package in R environment (Turner, 2016). Using the mentioned procedure, the total area of the stand was defined (0.0976 ha) and that is the growing space of the preserved homogenous group of trees at the age of 75 years with the initial growing space of 3 × 3 m (Figure 1).
The use of ’’Voronoi’’ polygons enabled the segregation of different collectives of trees that were under the different influence of neighbouring trees, i.e. the segregation of the collective of inner trees (A) and the edge trees (B) with their respective growing space (Figures 2 and 3).
Measurement and data analysis of growth elements – Premjer i analiza podataka o elementima rasta
At the age of 75 years, all the living trees that could have been linked to the trees from 1932, i.e. 1948 in the culture were permanently marked and periodically measured in the coming period. At the ages of 75, 80 and 85 years, two cross diameters with precision of 1 mm were measured as well as the tree heights using the Vertex III hypsometer with precision of 0.1 m. The thin trees that were present in the stand as a result of subspontaneous expansion caused by the decomposition of the stand were not included in this research.
On the area of 0.0976 ha at the age of 75 years, there were 54 trees in total, and at the age of 85 years (in 2017) 49 trees were still in the culture. These trees were the available sample that was used for the presentation of the growth elements of the trees and the stand per hectare.