engleski

Oak forest tending in Croatia with special emphasis on thinning intensity

Oak forests in Croatia have a natural structure because they have developed by natural regeneration with shelterwood system in two or three cuts. Regenerative silvicultural treatments of oak forests are divided into three groups. The first one involves activities dealing with preparing the site for natural or artificial regeneration. The second one comprises activities involving natural regeneration with shelterwood fellings, a method used in regenerating the majority of oak forests. The third one involves artificial regeneration, which is conducted only when acorn yields are inadequate, and is based on the principles of natural regeneration, that is, on shelterwood fellings in two or three cuts, and on the introduction of acorns or oak seedlings. Tending of oak stands begins the moment a young crop appears in the area being regenerated during shelterwood fellings. Individual regeneration activities, e.g. site preparation, can at the same time serve as tending operations on the seedlings and young growth sprouting before or during the regeneration period. The first steps in a systematic tending of oak forests in Croatia began at the turn of the 19th century, and have continued with increasing intensity until the present day. Tending of oak stands not only improves site conditions, but also encourages the replacement of the natural, spontaneous tree selection in a stand with the selection based on silvicultural principles. There is the negative selection, during which more light is brought to the young growth, and cleaning is carried out at the stages of an older crop and a younger stand. The positive selection, or the selection in the form of thinning, is done at an older stage of the young stand, in young, middle-aged, mature and old stands. Tending maintains the natural structure, and ensures coherence, productivity, sustainability, stability, diversity and the capability of natural regeneration. In order to achieve an optimal structure and a maximal increment, the basic wood volume of thinned stands should increase with age, which means that the wood volume cut in thinning operations should be lower than the current annual increment, and should reach the maximum value of an average age increment. In oak forests, the current increment exceeds the average age increment until trees are 160 or 170 years old. The maximal amount of wood volume to be cut with thinning is obtained if a given wood volume of a stand is divided by the age expressed in decades, that is, the age class; thus, Vt = Ve/n. Using this formula, we can arrive at the thinning intensity I = Vt/Ve x 100, that is, I = 1/n x 100, where Vt is the wood volume of thinning, Ve is entire wood volume of the stand being thinned, and n is the age class, or stand age expressed in decades.

Oak; tending; thinning; thinning intensity

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