Investigation on effective factors influencing distribution of wild pistachio species at Zanjan province

In order to study the effective factors influencing distribution of wild pistachio species in Zanjan province, the first step was to inquire and review all the related documents and information. The next step was to make excursion in the natural habitat of the species located in the study area. Finally, the distribution of the species was overlayed on topographic maps. The total area of this species estimated to be 23208 ha. Considering the main factors including: elevation, aspect and geological formation; working units were specified and 40x40 m sampling plots were located on the units to determine different forest types. Three forest types were distinguished, including: pistachio-juniperus (5002 ha), pure pistachia (3401 ha) and degradaded open pistachio (14805 ha). The last one was the vastest forest type which demonstrates the degradaded extent of this forest type. Most of trees at the forest types were coppice and only few seed originated seedlings were found. The highest distribution (44%) was found on 45 percent and higher slops. About 65 percent of the forests located on northwest and southwest aspects. The lowest distribution was found on the main aspects (north, south, west and east). Approximatly, the most distribution was found in cold semi-arid climate (61.74%) and the lowest distribution (0.16%) was seen in the cold-humid climate. Most of the forests were located on volcanic, shaill and sandstone geological formations (45.94%).