The Effect of Depth and Aspect on Soil Moisture in Dieback Affected Oak Forests (Case study: Meleh siah Forest, Ilam Province)

Recognition of humidity changes is important because of its relevance to hydrological, ecological and physiographic characteristics of the area. Therefore, soil moisture content in four main directions and three depths of 50, 70 and 110 cm of soil for two years from March 2013 to September 2012 in the forest area of Meleh-Siah Ilam was measured and analyzed in a randomized complete block design with soft SAS was implemented. The results showed that soil moisture and soil depth and direction were affected by moisture storage in the south and north directions with 21.9 and 19.7 and in the eastern and western slopes 19 and 15.5 mm. Also, the average monthly moisture content in the three depths of 70, 110 and 50 was 18.4, 17.4 and 7.5 mm respectively. The average monthly soil moisture storage at three depths 50, 70 and 110 are 18.4, 17.4 and 7.5 mm, respectively. In other words, the effect of soil depth and geographic orientation on the soil moisture is effective but not noticeable in dry years and in dry months. Also, the results showed that the monthly dryness rate (from wet to dry period) in the wet year is more than dry year and increases with increasing depth of soil. Based on soil texture analysis, the optimum moisture content for plant growth was between 15% and 30%, and based on this, the maximum drought stress on vegetation and especially oak species was in August and September, which coincided with the peak of vegetative growth And the reproductive stage of the oak tree species.