The purpose of the present study was to evaluate the genetic variability and heritability of some morphological and physiological traits in Fagus orientalis Lipsky along an elevation gradient in northern forests of Iran. Beech leaves were sampled from southern and northern crown parts of healthy mature trees along an elevation gradient comprising sites situated at 700 m, 1,200 m and 1,700 m above the sea level. Our statistical analysis showed that the investigated traits differed significantly between the populations. The results indicated the lowest and the highest coefficients of variation for the high (1,700 m) and middle elevation populations (1,200 m) for leaf length, petiole length, leaf area, specific leaf area, dry weight, specific dry weight, leaf index and petiole index traits. With increasing elevation, mean leaf width, distance from leaf base to the leaf maximum width, dry weight and petiole index increased. The plasticity of leaf length, specific leaf area, specific dry weight, petiole index and petiole length peaked at middle elevation, and with increasing elevation, the plasticity of these traits declined. The distance from leaf base to the leaf maximum width had the highest coefficient of genetic (75.5%) and phenotypic (75.5%) variation. The heritability results showed that there were differences in all traits, and that the highest heritability was recorded for the distance from the leaf base to the leaf maximum width (99.95 %). The results suggest that the studied beech populations responded to the environmental changes by changing their leaf traits in different ways at different altitudes.
