Spatial variations of diameter of Pistacia atlantica (Desf.) trees in Zagros area (Case Study: Pirkashan, Kermanshah)

In order to better identify the structure of Pistacia atlantica stands in Zagros forests, diameter structure was analyzed using geostatistics technique in a pure stand of Pistacia atlantica. For this purpose all the trees in the stand were mapped and their stem diameters were measured at breast height. Diameter distribution showed that more than 90% of trees belong to diameter classes 25 to 80 cm. Furthermore, no tree was observed with the DBH<16 cm because of unsuccessful establishment of regeneration during the last decades. An omnidirectional variogram was used to variography because of the no sign of anisotropy. An exponential model was fitted to the experimental variogram and then estimations were mad using ordinary kriging. Ripley’s K function was used to survey trees spatial pattern. Results indicated an average spatial structure for DBH in this stand with lag distance 15 m and effective range 85.2 m. The spatial pattern of trees was aggregated confirming the positive correlation between trees. It implied that unsuccessful establishment of regeneration and the quality of seedbed resulted in the existing of this spatial structure. Because on one hand there was no tree with DBH<16 cm and on the other hand trees with DBH<40 cm were just observed in rocky places between stones.