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ŠUMARSKI LIST 9-10/2023 str. 51     <-- 51 -->        PDF

transformed by arcsin√X transformation with the aim of complying with the normal distribution, as a presumption for applied parametric statistics. The average value for each subplot was the basis for further statistical analysis that was performed with the Statistica® software (TIBCO Software Inc., 2020).
The assessment of the damage caused by the oak lace bug on untreated subplots performed at the end of June 2019 showed higher damage of the leaves on shaded seedlings compared to unshaded amounting 56,2% and 0,4% respectively (Fig 3). July assessment showed the increase of the damage on both shaded and unshaded untreated subplots, while the August results showed that 99,4% of the damaged leaves on the shaded seedlings, compared to 41,8% of the attacked leaves on the unshaded untreated seedlings.
Results of the damage assessment on the oak leaves of shaded seedlings in late June of 2019 showed higher damage intensity when compared to 2020 and 2021. On the other hand, unshaded oak seedlings showed low damage intensity in June of 2019; 2020 and 2021 indicating the lower number of overwintered adults of the oak lace bug. July assessment showed significant increase of damage on oak leaves of shaded seedlings when compared to June. The values for the August assessment of the damage intensity on shaded seedlings varied from 88,1% (2021) to 99,9% (2019) with statistical differences between 2019 and 2021 values. Highest percentage of damaged leaves at the end of the August 2019 compared to the end of August 2020 and 2021 can be explained by warm spring in 2019 that positively affected the development and the reproduction of the oak lace bug combined with the low leaf mass of the young seedlings in 2019. Although varied, the damage intensity on unshaded seedling did not show significant difference. Obtained results for August assessments in 2019, 2020 and 2021 indicate two-fold higher damage intensity in shaded seedlings compared to unshaded ones. Such results indicate lower susceptibility to the oak lace bug leaf damage on the oak seedlings that are developing without the presence of the adult trees from the shelterwood regeneration system.
According to Paulin et al. (2021), most of the adults of oak lace bug are overwintering on the trunk and branches of the adult trees or on dead timber on the ground, with fewer number overwintering in the litter. Considering above mentioned, we hypothesize that the lack of the standing old trees and logs creates unfavorable conditions for overwintering of adults of the oak lace bug. In addition, crowns of adult trees present the source of the insects that can potentially cause damage on the young oak seedlings.
Statistical analysis showed that there was no significant difference regarding the average height of the oak seedlings in 2019 between the treated or untreated plants within both plots (shaded vs. unshaded) (Fig. 4, 6). On the other hand, differences between shaded and unshaded seedlings were significant in both treated and untreated plants. Such result can be explained by the more favorable growth conditions for unshaded seedlings, especially considering the heliophilous nature of the oaks. Such difference was even more evident in the following years.