Effect of the defoliations of Lymantria dispar on the cork growth
Abstract: The gypsy moth, Lymantria dispar, is the most important defoliator of the cork oak forests in North Africa. The moth larvae can cause partial or total defoliation of oak stands. This study aims to estimate the impact of defoliations on cork growth. Three areas that suffered increasing defoliation rates in two consecutive years and a control area without defoliation have been identified and 30 trees randomly selected in each. From each tree, 4 cork stops were collected at 1.30 m above the ground from every cardinal direction (480 stops).Results showed that cork growth did not vary significantly between cardinal directions but was severely affected by defoliation. The cork production losses were estimated based on the diameter class of tree trunks and defoliation index. The loss was minimal (not exceeding 13%) in cork oaks of small diameters (less than 50 cm) and higher when tree diameters were beyond 50 cm. Loss reached about 30% for trees having 50-60 cm in diameter and having suffered a partial or total defoliation. For cork oaks having 60-70 cm in diameter, cork loss reached about 30% after partial defoliation and more than 50% after total defoliation. Finally, for trees whose diameter exceeds 70 cm, cork loss exceeds already 60% after partial defoliation.