Four-year monitoring of crown dieback variations of Persian oak trees in relation to individual and site characteristics (Case study: Meleh-Siah forest, Ilam province, Iran)

The present research aimed to investigate the crown dieback of Persian oak trees in relation to their individual and site characteristics, evaluated the changes in crown health of trees during the years 2019 to 2022 in Meleh-Siah forest in the northern half of Ilam province. Two sites were identified in the northern and southern aspects and 100 oak trees were marked in each site. The characteristics of each tree, including the diameter at breast height, tree height, max and min crown diameter and tree origin were measured and recorded. The dieback condition of tree crowns was evaluated and divided into four classes of crown dieback. The evaluation of crown dieback of trees was done during four years and in September. The results showed that the highest abundance of trees in the northern site is in the classes of declining and crown dieback up to 50%, and in the southern site is in the class of crown dieback more than 50%. The number of trees leaving the healthy and declining classes was higher, respectively, which were transferred to the higher crown dieback classes. The healthy and declining classes were associated with decreasing changes and the crown dieback less than 50% class was associated with increasing changes. dbh, height and crown area of ​​healthy trees were lower than those of other crown dieback classes. The frequency of crown dieback was higher in denser stand. The rate of crown dieback was higher in coppice trees than in standard trees; in addition, the temporal changes of crown dieback were more in coppice trees. It was concluded that individual and social traits and environmental conditions had a considerable impact on the crown health of oak trees and how they reacted to recently happened droughts.