INSTYTUT DENDROLOGII

Abstract: Quercus robur and Q. petraea are important forest-forming species in Europe. Q. robur is believed to require more fertile soils, to be more tolerant to low temperatures and more sensitive to oak decline than Q. petraea. Thus chronologies of the two species from nearby localities were hypothesised to differ more strongly between species than between localities. Wood cores were collected on 23 research plots in 2 national parks and 12 forest districts. In each locality two plots (one with Q. robur and one with Q. petraea) were established in forest stands of similar age at similar site conditions wherever possible. Similarity between chronologies was assessed by the test of parallel agreement (Gleichlaufigkeit), Pearson correlation coefficients, and principal components. The plots were grouped by the Ward clustering method and according to 1st and 2nd principal components. The first 2 methods segregated chronologies nearly ideally into pairs of species from the same forest district, indicating that the chronologies differ between forest districts but not between species. Chronologies clustered in 2 large groups: northern and southern (on the basis of correlation) or northeastern and southwestern (on the basis of parallel agreement). Principal components also distinguished northeastern and southwestern chronologies, but less clearly. The results suggest that differences in climatic and soil requirements between the 2 oak species are generally too small in comparison with the differences caused by climatic factors.