effect of the oak leafroller moth, tortrix viridana l. on diameter growth increment of lebanon oak (quercus libani oliv.) in piranshahr and sardasht forests

abstract the oak leafroller moth , tortrix viridana l. is a destructive pest within it’s spreading area which invades the oak species, especially in west and northwest forests of iran, in recent years. some parts of west azarbayjan’s forests which are located in piranshahr and sardasht region have been affected by this pest since 1989 that oak trees vigor and survival have been gone down resulting the pest outbreak anually. in this study, 2 forest sites were chosen primarily which the first one was located in infested area (ca. 20 ha) and the second one was in non-infested area ( as a control, ca. 5.5 ha). in each site, 10 trees of lebanon oak (q. libani oliv.) were selected using transect method and a core was brought out from each tree employing increment borer. after preparing the cores, tree ring width was measured and after that comparing of the mean tree ring width between two sites ( infested and control) and correlation between them and climatic data (precipitation and temperature) were determined. the results showed that the mean tree ring width in the infested site was decreased significantly after outbreak while this significant reduction was not seen in the control through an eleven years period (1998-2008). also the pest outbreak caused tree ring width reduction of lebanon oak 35% as compared with the period before outbreak. lack of any correlation between tree ring width and climatic data could be considered as a reason which indicates the oak leafroller moth can cause tree ring width reduction, so control measures should be taken into account immediately.