Presented study is focused on the analysis of the slenderness of common birch (Betula pendula Roth.), growing at the mixed fresh coniferous forest site type. Data were collected on three plots being the part of the permanent experimental plot of the Silviculture Department, located at the Siemianice Experimental Forests. Trees characterized the high values of the average slenderness index, s = 1.31 [m·cm^-1]. Results showed that s index is correlated with few biometric traits of trees. The highest correlation was observed in between s index and diameter (d_1.3) and crown width (d_k). The static of trees in the unmanaged 30-years old stands was not stable what can potentially be susceptible for wind and snow damage.

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