Effect of tree decline and slope aspect on the leaf morphological traits of Persian oak trees

This study was accomplished with the aim of investigating the effects of tree decline and slope aspect on leaf morphological traits and determining the indicator morphological traits that indicate the leaf diversity of Persian oak trees in relation to habitat conditions and environmental stresses in Mellah Siah forests of Ilam. Two forest habitats were selected on the northern and southern slopes of the Mellah siah Mountain and at the same altitude range. In each habitat, 20 standard oak trees were randomly selected. These trees were divided into four classes of tree decline and five trees were placed in each decline class. From each tree, 20 leaves were separated from the four main sides of the tree crown, from the middle height of the crown and from the end branches as a combined sample in August. Samples were transferred to the laboratory to measure leaf morphological traits including leaf length, leaf width, petiole length, leaf shape, number of right leaf teeth and number of main veins. The results showed that leaf length under the influence of tree decline and other studied leaf morphological traits under the influence of tree decline and slope aspect had significant changes. Accordingly, leaf length in healthy trees was less than other classes of tree decline. The values ​​of leaf width and number of teeth on the right leaf side were higher in the northern habitat and the values ​​of petiole length, leaf shape and number of main veins was higher in the southern habitat and how these traits changed among tree decline classes was different in both slope aspects. The plasticity study showed that the petiole length trait has the most plasticity and is more affected by the environment. Therefore, it was found that the leaf morphological traits of Persian oak trees are significantly affected by habitat environmental conditions and tree decline, and the petiole length is an indicator of leaf diversity of Persian oak trees at the habitat level, although at the tree classes level all studied traits were involved.