Distribution of Pistachio mutica F. & M. as Influenced by Topographical Factors and Soil Properties in Mountain Areas of Western Iran

Abstract

Forests of wild pistachio (Pistachio mutica F & M) are widely distributed throughout most parts of Zagros mountain ranges of Iran. Covering an area of 2.4 million ha, the forests have experienced a high degree of human disturbance over a long period of time. These plants have edible fruits with extractable juice usable in pharmaceuticals, gums, paints, pesticides, pastes, perfumes and mineral oil industries. The Ghalajeh heights of Kermanshah province, an extension of Zagros ranges are one of the famous and main habitats of these species. The purpose of this research was to determine the effects of soil properties, elevation levels, slope gradients and positions on habitat distribution of wild pistachio in Ghalajeh heights. A defined forest area was divided into the 100 m elevation intervals and a quadrate (50 x 50 m) method was used at each interval. Plant distribution was significantly correlated with soil P and clay content, soil depth, and slope position, however, slope gradient, soil organic carbon (C) and pH had minor influence on plant distribution. The wild pistachio plants were the dominant species at elevation levels of 1500 to 2200 m and there were no pistachio trees at above 2220 m and below 1380 m elevation. Slope aspect had a prominent effect on plant growth and their distribution. There was higher plant density in the north-facing slopes than others. Canonical correlation analysis showed that increased soil P and decreased silt contents strongly increased canopy closure, hrowever, soil P content had not very significant effect on plant density. Elevation level increased plant density, but the rate of increase on annual shoot growth was less than plant density. Increase in annual shoot growth was primarily due to soil depth.