the mean fiber length of three beech trees (fagus orientalis l.) at the lower and higher points (1% and 75% tree height) of the stem at an intermediate altitude (500-1000m) in the caspian forests in sari region were 1.36 and 1.22mm respectively, close to the values in three trees at high altitude (1000-1500m), that were found to be 1.39 and 1.36 mm. the mean fiber lengths of the whole stem, usi...