In the present study, needle variation of Scots pine (Pinus sylvestris L., Pinaceae) populations in Turkey was investigated. From selected eight populations, a total of 1314 needles belonging to 206 trees were examined. Four morphological needle traits were measured and analyzed to describe the population diversity and differentiation. Analyzed morphological traits showed significant variability. The trees within populations differ significantly in all analyzed needle characteristics, while the differences between populations were significant for the three of four studied characteristics. Present findings revealed that needle length, needle width and the ratio of needle length to needle width showed clinal variation in response to altitudinal gradients. Populations from higher altitudes were characterized with the smaller and wider needles as compared to the populations from lower altitudes. The results of this study could be valuable baseline data for the development of more efficient management plans for this forest tree species.

In this study, eight Scots pine populations from Turkiye were studied to explore the influence of different habitats and altitudinal zones on the needle anatomical traits. A total of 496 needles belonging to 64 individuals were examined using light microscopy with the aim to score variability of sixteen needle anatomical traits. Variance analysis showed significant differences in needle thickness, needle width, resin canal number, resin canal diameter, central cylinder width, central cylinder thickness, endodermis cell number, endodermis width and endodermis thickness of eight populations depending on habitat zones. However, only resin canal diameter, endodermis width and endodermis thickness differ significantly in examined populations depending on altitudinal gradients. Cluster analysis showed the greatest similarities between the Bolu-Aladağ and Ardahan-Yalnızçam populations, and the most distinguishable population was the Giresun-Espiye population based on the anatomical characteristics of the needles. Although principal component analysis showed that needle width, central cylinder width, needle thickness, and central cylinder thickness had the greatest influence on the delimitation of Scots pine populations distributed in Turkiye, discrimination analysis did not separate the examined populations depending on the anatomical characteristics of the needles.