INSTYTUT DENDROLOGII

Oak is the most common broad-leaved tree in Poland. According to data from 1993, forest stands of oak, ash, maple, sycamore and elm cover account for 6.1% of wooded area. Although for many years it has been suggested that Quercus robur and Q. petraea should be separated in breeding and cultivation, both statistics and the operating principles of silviculture make no distinction between these two forest-forming species. Q. robur has slightly lower thermal requirements but needs a more fertile soil than Q. petraea. Observations made recently indicate that forest stands of Q. petraea are less prone to oak decline. The aim of this work was to determine if the above differences are reflected in different radial growth dynamics of the two oak species, and if the differences in their reaction to stress factors provide an explanation to their different sensitivity to oak decline.

Material for this study consisted of wood samples taken with the use of Pressler's borer at breast height from trees growing on 23 plots established in oak forest stands in central and northern Poland. Ring width measurements were exact to 0.01 mm. The results were verified and analysed according to standard dendrochronological methods.

Dendrochronological analysis is based on an assumption that changes in the width of annual growth rings result from interactions between the individual and environmental factors. Thus ring width is a combined effect of favourable and unfavourable factors on a given tree characterized by a specific genetic potential and growing in a specific site.

The results of this study did not reveal any difference in reaction to the analysed stress factors between the two oak species, as the similarity between mean growth curves for individual plots did not depend on species. The similarity depended mainly on the distance between plots and their location.

Moreover, the results of this study showed that periods of oak decline had a long-term negative effect on the rate of radial growth in some individuals. The number of such individuals was similar in both species.