The study comprised an analysis of two tree stability indexes, i.e. slenderness factor (H/D_1.3) and crown inclination index (D_K/H) of thirty six pines coming from twelve mature stands growing at diff erent sites. Apart from stability for each tree tracheid wall thickness was determined at breast height in early and late wood. Results showed that examined trees belong to a group considered to be stable (Figs. 2, 3), while investigated stability indexes are negatively correlated (−0.64). Next tracheid wall thickness was determined in early wood to be 2.11 ±0.21 μm and for late wood at 6.84 ±1.08 μm. No significant differences were found between examined plots in terms of investigated indexes or tracheid wall thickness in late wood. In contrast, statistically significant dependencies were observed between the analysed indexes and tracheid wall thickness in early and late wood. Slenderness factor was most strongly correlated with tracheid wall thickness in late wood. Moreover, a dependence was also found between crown inclination index and tracheid wall thickness in early wood, which most probably may be explained by the relationship between the tree crown, which width was one of the variables in D_K/H and hydraulic functions of anatomical elements. With an increase in the crown inclination index the mean tracheid wall thickness decreased, most probably leading to an increase in their lumen, which has a positive effect on their efficiency in conductivity of water and minerals.

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