Variability of earlywood vessel row number of pedunculate oak (Quercus robur L.) and common ash (Fraxinus excelsior L.) in response to external factors

Dendrochronological analysis of oak (Quercus robur L.) and ash (Fraxinus excelsior L.) trees sampled in Kozelsk Zaseki allowed us to reconstruct the disturbance history of a part of this forest area for the last 150 years. Large and medium scale disturbances were detected in 1868, 1940, 1957, 1971 and 1977. In the last case, the results of the dendrochronological analysis are supported by archival documents. It is shown that after disturbances both studied species show significant increase in the percentage of tree-rings with higher number of earlywood vessel rows. Similar changes in anatomical structure may occur in response to extreme floods and winter frosts. Possible mechanisms of the formation of the studied anatomical features are considered.