Growth dynamics of crown shapes in stands of pedunculate oak and common hornbeam

Background and Purpose: Structure of crowns in forest stands is one of the main factors which determines growth and development of trees. Dynamic change occurs with the age of the stand due to silvicultural interventions or natural disturbances during which trees are removed from the stand. The aim of this article is to analyse the structure of the crown shape of pedunculate oak and common hornbean trees with regard to diameter at breast height (DBH) and the age of the stand in one of the most important forest community in Croatia. Materials and Methods: The investigation is based on data collected on 47 permanent experimental plots which were established as a chronosequence in a natural range of forests of pedunculate oak and common hornbeam in Croatia. The total surface of all plots amounts to 33.45 ha. Breast height diameter, tree height and stem height were measured on the trees in the experimental plots, and a detailed ground plan was made of horizontal crown projections, from which the crown diameters were calculated. In total 1505 pedunculate oak trees and 2026 common hornbeam trees were measured. For each tree the crown shape was calculated and trees were then grouped in age classes of 20 years, and the shape of the crown analysed according to species and age classes. Correlation between crown shapes and diameter at breast height was investigated for stands of the sixth age class (101 – 120 years) for each species by means of linear regression. Results and Discussion: The shape of the crown of pedunculate oak, although it shows a trend toward growth in relation to diameter at breast height, the regularity pattern of the shape indicates weak character (r=0.441), i.e. variability is explained with only 19%. Crown shapes of common hornbeam are almost constant in relation to diameter at breast height (r=114), and correlation between the examined values cannot be equated by any rational analytical term. Investigation of growth dynamics of crown shape structure was carried out according to the species of trees and age classes, and the interval in which 68% (x ± 1.0 s) and 95% of data (x ± 1.96 s) were included. Conclusions: The results of the investigation indicate that dependence on crown shape and diameter at breast height of pendunculate oak and common hornbeam cannot be described by any rational analytical term. Average values of the crown shapes according to age classes can be used as form factors for calculation of crown volume. Data are applicable in various applications, such as for example their integration in a simulator of growth and development of forest stands and examination of the effect of different silvicultural scenario. TOMISLAV DUBRAVAC MARTIN BOBINAC DAMIR BAR^I] VLADIMIR NOVOTNY SINI[A ANDRA[EV Department of Silviculture Croatian Forest Research Institute Cvjetno naselje 41 HR-10450 Jastrebarsko, Croatia University of Belgrade, Faculty of Forestry Kneza Vi{eslava 1, Belgrade, Serbia Faculty of Forestry University of Zagreb Sveto{imunska 25, p.p. 422 10002 Zagreb, Croatia Department of Forest Management and Forestry Economics Croatian Forest Research Institute Trnjanska 35, 10000 Zagreb, Croatia University of Novi Sad Institute of Lowland Forestry and Environment Antona ^ehova 13d, Novi Sad, Serbia Correspondence: Tomislav Dubravac, PhD Department of Silviculture Croatian Forest Research Institute Cvjetno naselje 41 HR-10450 Jastrebarsko, Croatia E-mail: [email protected]