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The Black Cherry (Prunus serotina Ehrh.), a North American forest tree, had been extensively planted for timber production in order to improve soil quality in pine plantations in European forests during the first half of the 20th century. Unfortunately, it failed to meet the foresters’ expectations. It has instead spread rapidly in silvicultures becoming a notorious weed species, difficult to control. Although it still has alien plant status, it seems that 150 years of its presence on the European continent might suffice for this neophyte to become adopted as a host plant by the native fauna of insect herbivores. The observations of Prunus serotina were conducted in 2009–2010 in the Rudno Forest District, Lower Silesia, Poland, on Prunus serotina plants growing as a thick understorey shrub layer in fresh mixed deciduous forest. The analyses, performed in 7–10 day intervals from April until the end of July each year, aimed at monitoring the population dynamics of Gonioctena quinquepunctata on P. serotina plants, and the dynamics of leaf perforation caused by this herbivore, in order to determine the relation between these two species. The insects were observed on 100 shoots on 10 plants on each observation date, and were recorded in situ. Based on the estimates of the leaf damage, the mean perforation index (PI) (%) was calculated on each date for each plant shoot, expressed as the mean percentage of the perforated leaf blade area. PI (%) was subsequently correlated with the beetle and larvae density on the plants. It has been demonstrated that the feeding of G. quinquepunctata on Black Cherry plants is more closely associated with the presence of its larvae, than with that of the beetles. Although the mean PI value on each observation date was never higher than 12%, the maximum perforation of individual leaf blades occasionally exceeded 50%, whereas the maximum mean PI calculated for individual shoots on each observation date reached as much as 47%. The authors suggest that feeding of G. quinquepunctata on P. serotina may represent an example of a well established trophic link between a native herbivore and a plant species still considered a neophyte.
The different defence strategies of trees against herbivores are very often connected with succession status, leaf life span and the level of secondary metabolites. We examined the effect of simulated leaf grazing on the differences in the leaf life span and defence chemistry of two pioneer tree species that belongs to the same family (Betulaceae), black alder (Alnus glutinosa (L.) Gaertn.) and European white birch (Betula pendula Roth.). At the beginning of the growing season, mature leaves were perforated using a paper punch. The holes removed about 10% of the leaf surface. Each species was represented by six trees – one branch was chosen for perforation and one branch as a control. All leaves were counted every week until their abscission. Additional damages caused by grazing insects were also noted. Undamaged birch leaves were held much longer than those of alder. The average difference in half leaf life span between control and perforated leaves was 28 days in birch and 6 days in alder. The control unperforated alder leaves were significantly (P <0.05) more often grazed by insects than those that were perforated. Leaf perforation in alder increase phenolic concentrations in the new, young leaves. In birch we did not observe these changes. The comparison of alder and birch indicate that the species with similar successional status can have different strategies of leaf defence. The birch leaves were characterized by a longer leaf life span, constitutive defence, a lack of induced defence accumulation of phenolics and earlier shedding of damaged leaves in comparison to the control. The black alder foliage had a shorter leaf life span, induced defence reaction (produced more phenolics after perforation), and only slightly earlier shedding of damaged leaves than the control.
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