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Current state and the structural analysis of the mixed even-aged pedunculate oak and common hornbeam forests in Croatia

Mixed forests of pedunculate oak and common hornbeam are among the most important and most recognizable forest ecosystems in Croatia with exceptional ecological, economical and sociological significance. Stand structure of these forests can be very complex, and their development highly dynamic due to the relationships between the add-mixed tree species as well as vertical and horizontal stand structural elements. In the contemporary management of oak-hornbeam forests in Croatia growth and yield tables of domestic authors are used. Aim of this research is to give an overview of the current state of mixed forest stands of pedunculate oak and common hornbeam in Croatia through the analysis of available information on the area extent and basic stand structural features. Furthermore, the information obtained in the research are compared with the data from the growth and yield tables of domestic authors. Database used in this research is maintained by the state-owned forest management company Croatian Forests Ltd., and is comprised of the data collected within the regular forest management. In total, 5, 060 forest stands (sub-compartments) with total area of 75, 948.76 ha from whole area extent of pedunculate oak in Croatia were included in the analysis. Record for each stand included: phytocoenological community, forest area, stand age and age class. Width of the age classes is 20 years. Analyzed stand structural attributes were grouped for each stand by tree species (pedunculate oak, common hornbeam and other species) and as a whole, and included: stand density, basal area, volume, quadratic mean diameter and height. Finally, the shares of pedunculate oak and common hornbeam in the total basal area of each stand were calculated. Total area of mixed pedunculate oak and common hornbeam forests in Croatia, according to the results of this research, amounts to 98, 364.43 ha. Age structure of these forests is irregular, both by area, and by the number of forest stands with stands older than 80 years (5th age class and older) dominate in the total area. Most of the stands (> 68%) grow on 1st site class, i.e. the best site class. Structural elements of forest stands on 1st site class, show a large variation of the analyzed structural elements throughout the development of the stands (2nd to 8th age class). Highest variation is established in the shares of tree species in the total basal area of the stand. These values are under the direct influence of the growth and development of diameters at breast heights of trees of different species and of the corresponding diameter distributions. Basal area shares are also highly influenced by the silvicultural measures applied during the life- time of each particular stand. Comparison of actual stand structural attributes with the values indicated as optimal in the growth and yield tables of domestic authors revealed a high degree of discrepancy. As a general conclusion, it can be said that the currently used growth and yield tables only very rarely correspond with the actual state of forest stands in the field. New and improved methods of forest management planning are highly desirable at this moment in Croatian forestry.

mixed forest stands; pedunculate oak; common hornbeam; stand structural elements; basal area; growth and yield tables

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