engleski

Health status of sessile oak (Qurcus petraea Liebl.) in Croatia

The health condition of forests in Croatia has been monitored from year 1987 at 87 plots of 16x16 km network (Level 1) and 7 permanent intensive monitoring plots (Level 2). This is carried out in accordance with the methods of the International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests). The monitoring and assessment of defoliation of foliage on Level 1 plots showed that the percentage of significantly damaged sessile-flowered oak trees (moderately to severely defoliated- defoliation level 2, 3 and 4, i.e. defoliation over 25%) has risen from 2,3% in year 1987 to 44,8% in year 1997. This difference is largely the result of a shift in the highest frequency of trees (mode) from Class I (10 – 25% defoliation) to Class III (25-60% defoliation). In 1998, however, a drop of percentage of significantly damaged trees to 21,9% was observed and the mode “shifted” to Class II (10-25% defoliation). Once the current and following years’ defoliation data have been analysed, it will be possible to conclude whether a recovery in the sessile-flowered oak forests in the Republic of Croatia is taking place. Besides visual assessment of crown condition, research into the vegetational structure of the forest phytocenosis, the amount of precipitation present, the properties of soil, atmospheric deposition, cambial electrical resistance, foliar chemical composition and other parameters is undertaken on intensive monitoring plots. The interaction between the level of defoliation and the cambial electrical resistance of the sessile-flowered oaks has been ascertained. Measurements and assessments at permanent plot No. 102 – Goić, verified that trees with a low level of defoliation have a lower electric resistance (6,5-10,0 kΩ) than trees with a high level of defoliation (11,3-18,5 kΩ). In researching the condition of the sessile-flowered oaks’ crowns, a unique method of aerial photography is utilised. This is achieved with the aid of a special device for taking detailed aerial photographs of the upper section of the crown. Aerial photographs have been taken permanently on one of the seven intensive monitoring plots (No. 102-Goić). The aerial photographs show the foliation, blossoming and fructification phenophases, the health condition of the upper section of the crown as well as other events which are important for intensive scientific research.

sessile oak; crown condition; 16x16 km network plots; intensive monitoring.

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