Infestation of forest trees to the borer beetle and its relation to habitat conditions in the Persian oak (Quercus brantii) in Ilam Province

Recent drought stresses and subsequent trees physiological weaknesses had drastic effect on borer beetles population increase in Zagros forests. Shalam forests located in Ilam province was selected to investigate borer beetle infestation rate of forest trees to the under various site conditions and stand structure in Persian oak forests. The study area was divided into 20 units using GIS and random systematic sampling and 3 1000m2 circle plot in any single unit was established across the landscape. In each plot, tree diameter (DBH), mean crown diameter, source and form of trees and shrubs, crown dieback condition, borer infestation rate and site situation was measured. Results showed that topographic factors and stand characteristics have significantly affected contamination rate of forest trees to borer attack. The highest contamination percent of trees to the borer beetles was observed southward in 1700-2000 m elevation from sea level. There were positive correlation between elevation and beetle’s infestation. Slope did not show any correlation with amount and intensity of beetle’s contamination. Abundance of beetles was higher in coppice stands than standard trees. With increase in stand density and tree crown width, beetle’s intensity increased. Contamination intensity was higher in smaller diameter classes as well as in dieback prevalent stands. The results emphasized that borer infestation usually occur following severe droughts and drying and thus borer beetles are considered as secondary agents causing tree mortality. The results indicated that site and stand diversity affect borers’ infestation rate. Thus we can pinpoint the hotspots and apply appropriate measures for forest protection.