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ŠUMARSKI LIST 11-12/2014 str. 38     <-- 38 -->        PDF

4. Discussion
At least thirty four volume models are reported in Europe for Scots pine, from which more than half were developed for Scandinavian countries (Zianis et al. 2005). Comparing our models with the ones developed by Näslund (1947) (breast height diameter ranges between 5 and 49.9 cm, and total tree height between 3 and 32.9 m), we can demonstrate that volume - dimensions (D, H) relationship of the forest studied in the present research and of the forest studied in Sweden are comparable. Näslund’s models are:
                vˆ = 0.1028D20.02705D2H + 0.005215DH2                    (1)
                vˆ = 0.1072D2 + 0.02427D2H + 0.007315DH2              (2)
where total volume vˆ  is in dm3, breast height diameter D in cm and total tree height H in m.
For the common D and H ranges of both studies (Näslund’s and the present):  m and  m, volume is  m3 for model (1),  for model (2),  for site type A of the central part of the Rhodope Mountains,  for site type B and  for the studied area as a whole. The central part of Rhodope and the Swedish forest appear to have similar volumes for the same tree dimensions (D, H).
In an attempt to examine possible effects of distance between trees on form factor, we applied nearest neighbor analysis, a method used in forestry to assess animal damage to trees (Pepper 1998) and cavity tree abundance (Temesgen et al. 2008). Form factor is related to stand density (competition between neighbor trees) (Philip 1994) Nearest neighbor analysis revealed that trees of site type C are more isolated, compared with trees of site types A and B; based on the analysis, neighbor trees of the sampled trees were more distant than those of the site types A and B. This fact did no led to a lower form factor in the sampled trees of site type C compared with the trees of site type A, where a lower form factor and smaller distances between sampled trees and their neighbors were observed. This happened because the nearest trees to the sampled trees in site type A were beech trees with small dimensions. In most cases, in the mixed P. sylvestris – F. sylvatica stands of the study area, beech appears in the understory and in the middle story as a small tree. As a result, the competition imposed to pine trees was not significant, as well as the influence of beeches on the form factor of pines. The main influence on the form