Effect of slope aspect and crown dieback intensity on leaf and soil nutrient status in Persian oak stands, Quercus brantii Lindl. (Case study, Melah-Siah forests, Ilam province)

This study was done to investigate the effect of slope aspect and crown dieback intensity on the nutrient status of leaves of Persian oak trees influenced by dieback and site soil in the forests of Ilam province. For this purpose, the Forest area of Melah-Siah was considered and two one-hectare areas on the northern and southern aspects with almost the same altitude levels were selected. In each selected area, 10 trees were sampled in two intensities of healthy and dieback affected. Leaf samples were collected from the four main sides of tree crown and the middle part of the crown and from their terminal branches. Furthermore, from the south side of the selected trees, soil samples were prepared from two depths. Collected samples were transferred to the laboratory for analysis of OC, N, P, K, Ca and Mg.  The results showed that the slope-aspect and crown dieback intensities have significant effects on the amount of phosphorus, calcium and magnesium in Persian oak tree leaves. So that, the amount of leaf phosphorus in the northern site was higher than the southern site. Leaf calcium and magnesium concentrations were higher in the north site than the south site and in dieback-affected trees than the healthy trees. Also, the amount of soil organic carbon was significantly affected by slope aspect. The OC content in depth of 0-20 cm, in the northern site was less than the southern site. The amount of pH, CaCO3 and soil moisture in the depth of 0-20 cm and soil moisture in the depth of 20-50 cm were also changed under the slope aspect. It was concluded that leaf nutrients had more changes than soil elements under the influence of considered factors and the amount of these changes was more attributed to the slope-aspect. The studied Persian oak trees with different crown dieback degrees had a similar situation in terms of soil macro elements, but had different conditions in terms of leaf macro elements. Considering the differences between their habitats in terms of soil moisture and pH, it can be said that the dieback severity of tree crowns is related to physiological mechanisms in trees for absorbing water and nutrients.