Biometric indices of wild pistachio ( Pistacia atlantica Desf.) trees under resin extraction in Western Iran

Resin extraction from wild pistachio trees is an extant agroforestry practice in Western Iran. This practice plays a great socio-economic role in rural communities, but its effects on tree survival and forest stand persistence is still unknown. The objective of this study was to assess how this practice could affect the persistence of wild pistachio stands. Specifically, we (1) analyzed the biometric indices of wild pistachio trees under resin extraction vs untreated trees, and (2) evaluated the changes in the distribution of biometric indices classes of resonated wild pistachio trees. Two paired stands, including an unmanaged stand and a managed stand were selected. Tree species was recorded and diameter at breast height (dbh) for all trees (dbh ≥ 5 cm) was measured. Total height, trunk height, and crown diameters were measured in wild pistachio trees as well. Results indicated that the traditional method of resin extraction alters the frequency distribution of trees in all the biometric indices measured. The median dbh (36 cm and 26 cm in unmanaged and managed stands, respectively), total height (6.4 m and 5.1 m, respectively) and crown area (44.2 m2 and 23.3 m2, respectively) differed significantly between investigated stands. Trunk height (2.7 m and 3.2 m, respectively) and trunk height to total height ratio (0.43 and 0.62, respectively) were significantly higher in the managed stand. Resin-tapped trees reached a lower height and crown size for a given stem diameter, indicating that resin-tapping induce some kind of stress and/or consumption of resources that slow down tree growth.