Structural Characteristic of English Yew (Taxus baccata L.) Stands in the Afratakhteh Forests Reserve

      Taxus baccata L. is a native and ancient tree species growing the Hyrcanian forests that have been considered in recent years because of being in the red lists of threated species. The aim of this research was to provide quantitative characteristics of forest stand structure using a set of indicators in the natural habitat of this species. Three one-hectare sampling area were selected to reveal the quantitative characteristics of the yew stands structure. In the study area the 30×30 m gird plot was established. In the intersection point of girds (n=36) the closest beech to the intersection point as reference tree and other three nearest neighbors the to the reference tree was selected and diameter at the breast height, tree height, crown diameter, distance and angle among trees were measured .The set of indices including such mingling, diameter and height differentiation, tree to tree interval distance and Clarke and Evans index were employed to quantification of stand structure. Results showed that the uniform angle index value was 0.64 and Clarke and Evans were around one this means the yew randomly distribute in this forest. The mingling index estimated 0.61 that means English yew tends to mixed with other tree species. According to the diameter and height differentiation, yew stands have slightly heterogeneous diameter distributions, uniform tree height and the stems have an average distance between trees of 2.0-4.0 m. The English yew is a threatened tree species and in its natural habitat tends to be mixed with other species (often with hornbeam), have slightly heterogeneous diameter and height distributions. The reduction of young Yew trees as a result of the mortality of trees in a diameter classes less than 15 cm and the high competition of Yew with other tree species requires more consideration and effort to conservation of this species in the sites.