The paper presents results of research on changes of the variation of chosen true form factors of oak stems with age. There were 28 sample trees chosen by Darudt’s scheme in 80 years old oak stand. On these trees, when fallen down, the full stem analysis in five year periods were applied. The results of the analysis were used for calculating following form factors: f_L/15, f_L/10, f_L/9, f_L/8, f_L/7, f_L/6, f_L/5, f_L/4, f_3/10L, f_L/3, f_4/10L and f_L/2 under bark. The value of the b.h. form factor was also calculated for each stem for comparative purpose. The less variable form factors in examined stands were f_L/4, f_L/3 and f_L/5. Average values of their coefficients of variation were, correspondingly 9.01%, 9.08% and 9.09%. The highest variation was found for f_L/2 – 14,84% on average. The correlation between investigated form factors and d.b.h. under bark, tree height so as slenderness quotient have also been analysed. In most cases, the correlation between form factors and tree height, calculated in different periods of life, is weak, often statistically insignificant. Stronger correlation appears in later period of tree life (over 40 years) between true form factors f_L/7, f_L/6, f_L/5, f_L/4, f_3/10L, f_L/3, f_4/10L and d.b.h. under bark and slenderness quotient.

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