Journal of

Oak decline is a complex phenomenon that oak forests are faced with it across the world and Iran. Shalam forested area located in north of Ilam province was selectedto determine the role of topographicand some edaphic factors in tree mortality happened in Persian oak forests. The study region was divided into 20 homogeneous topographic units. Within each homogeneousunit,three 0.1-haplots  were randomly-systematically established for measuring the rate of tree mortality and oneprofile was prepared for characterization ofsome  physical and chemical soil characteristics (texture, moisture content, TNV%, OC% and N for each soil layer, and soil depth). In each plot,diameter at breast height (DBH), maximum and minimum crown diameters, crown dieback percent, origination and form of trees and shrubs for all species and site variables weremeasured. Results showed that 15.7% of forest stock had reduced while 97.65% of it belonged to Persian oak species. The results of multiple linear regression and RDA showed that tree mortality was significantly affected by elevation and aspect, but not by slope. The highestrate of tree mortality was observedin high elevation and south and west aspects. Also the results of multiple linear regression and RDA showed that tree mortality was significantly affected by soil depth and texture. So, the highestrate of tree mortality was observed in soils with less depth, less sand% and more silt%. It was concluded that topography and soil have effective role in tree mortality and its expansion across Zagros forests. Identifying the critical conditions in terms of topography and soil in these forests can help and be useful in the management of tree dieback.

To investigate some effective causes of beetle attack to Amygdalus scoparia in Bagh Shadi Harat, Yazd 80 sampling plots were randomly selected. In each plot number of infected tree, percent of dryness for each tree, height, diameter at root collar and crown diameter of each tree, elevation, slope and aspect of each plot were measured or recorded. Results showed that beetle infection were positively correlated to dryness of Amygdalus scoparia, Loranthus Grewinkii and negatively to tree sprouting. Beetle infection were also positively correlated to density of Amygdalus scoparia, density and coverage of accompany species, number of dried Amygdalus scoparia and negatively to percentage of slop. It is concluded that beetles prefer habitat with denser and more coverage population of Amygdalus scoparia in flat area and on trees with less sprouting. Since the study area is an important conserved place in Yazd province, research to control the pest can be very important. Elimination of effected and old trees may limit growth of pests in this area.