engleski

The relation between stand elements of pedunculate oak forests and growth yield tables in Croatia

With 285, 071 ha and a growing stock of 60, 600, 000 m&sup2 ; , Croatian floodplain and lowland forests account for 16% of the total forest area and 19% of the growing stock. Owing to great significance of these forests, they have long been the objects of intensive management and research. In view of recent disturbances in the climate, destruction of the ecosystem stability, changes in site conditions and stand structure caused by hydro-technical interventions into the region, normal and increment yield tables in these forests are not static but changeable values over a period of time. In the region of lowland forests in Croatia there are 202, 150 ha of pedunculate oak forests consisting partly of pure stands of pedunculate oak (20%) and of mixed stands of pedunculate oak with ash and pedunculate oak with common hornbeam. In Croatia there are growth-yield tables for non-mixed stands of pedunculate oak, ash and hornbeam. Using a mathematical procedure to obtain mixed growth yield tables from non-mixed growth yield tables for a certain mixture ratio is not a correct procedure, because a mixed growth yield tables should be the result of complex and changeable relationships among tree species during the development of a mixed even-aged stand. For this reason, mixed growth yield tables should be constructed, which should take account of complex relationships among tree species during the development of mixed stands. 10, 652 compartments of non-mixed and mixed stands of pedunculate oak with narrow-leaved ash and hornbeam were taken from the Croatian forest database. The stands were divided into three classes according to site quality. Four groups were formed within each class according to the mixture ratio of the principal species (pedunculate oak) and subordinate species (narrow-leaved ash or hornbeam). For each of the 10, 652 stands data were taken on the mean height, mean diameter, number of trees per ha, volume per ha, and current increment per ha. By inserting these stand elements into the age function within each individual group, relationships among the "averages" of real mixed even-aged stands according to the existing non-mixed growth yield tables were studied, as well as the methodology of constructing mixed growth yield tables. The obtained result shows that the "average" stand elements of the forests under study deviated considerably from the existing growth yield tables. This research should be viewed as preliminary, because it is based on the data collected for the purpose of drawing up management plans, and not on the data from permanent and temporary experimental plots.

lowland forests; forest management; mixed stands; growth yield tables

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