Morphological traits variation of needle in males and females yew (Taxus baccata L.) in the Hyrcanian forests of Iran

In this study, the diversity of morphological traits of needle in male and female yew (Taxus baccata L.) along the topographic and longitude gradients in the Hyrcanian forests was studied. To this aim, a total of 580 needles from 58 trees were measured in three sites (Amlash, Gazu and Afratakhteh) along the longitudinal gradient of the Hyrcanian forests. A hierarchical or nested analysis of variance was used to assess influencing sex and site on the 6 measured morphological traits of needles. In addition, Duncan's test was used for multiple comparisons of means. Furthermore, principal component analysis (PCA) was used to determine the most important traits and environmental factors in differing sites. Results showed that variation of morphological traits of yew needles is only affected by site factor. However, the influence of sex was not significantly assessed. Results also showed that most morphological traits of yew needles except the form factor were highest in Gazu site that comprised moderate slopes, northern aspects, faced northern humid air and experienced higher growing season due to lower elevation. Generally, morphological traits of yew needles were lowest in Amlash site, which included steep slopes (loss of soil depth) and western aspects (decrease in relative humidity). Yew trees in Afratakhteh site showed intermediate values. Our results imply that sites with cool summers and higher relative air humidity (settling in the humid northern valleys) provide more favorable growth conditions to morphological traits of yew needles compared with sites with higher average annual rainfall across the Hyrcanian forests.