The relationships between the rate of oak trees decline and forest types, soil characteristics and topographic conditions in Ghalaje Forests of Kermanshah, west of Iran

In order to investigate the decline of oak trees in Zagros forests in relation to forest soil characteristics and topographic conditions, Ghalaje Forests with an area of 500 ha in Kermanshah province were selected. For forest classification, systematic-random sampling was used with a 200×150 m grid by 50 m transects. Work units were specified based on the land form, aspect, altitude, slope degree and rate of oak decline. Soil samples were taken within work unit to analyze soil texture by hydrometer, soil nitrogen by Kjeldahl, bulk density by clod method, organic carbon by Black and Walkey method and lime percentage with Calcimetri method. The results of analysis of variance showed that the number of dieback trees was significant (P < 1%) in different types, slopes, aspects × types, altitudes × aspects and slopes × aspects. Correlation was found between the number of dieback trees and soil moisture and texture (P< 5%), and with bulk density, pH, soil carbon and nitrogen (P < 1%). However, no correlation was found between the numbers of dieback trees with C/N. We concluded that severe tree mortality occurred at shallower soils with lower organic matter and nitrogen contents, steeper slopes, warmer aspects and most pure forest types. The results will help to perform successful rehabilitation, restoration, and forest plantation projects and will be useful in the management of declined oak forests