Tree-ring chronologies of downy oak (Quercus pubescens), pedunculate oak (Q-robur) and sessile oak (Q-petraea) in the Bielinek Nature Reserve : comparison of the climatic determinants of tree-ring width

In 2004-2006, 50 trees of downy oak (Quercus pubescens), pedunculate oak (Q. robur) and sessile oak (Q. petraea) were sampled in the Bielinek Nature Reserve. The following chronologies were established from their tree-ring series: OMS of 212 years (1793-2004) for downy oaks well as D10 of 183 years (1817-1999) and D13 of 211 years (1789-1999) for the two indigenous oak species pedunculate and sessile oak, respectively. These chronologies were used for signature years and response function analyses. All three chronologies were highly similar, which points to identical responses to the ambient meteorological conditions. The radial increment of downy oak depends primarily on the amount of precipitation. A high annual sum of precipitation, copious rain in springsummer in particular, results in wide tree rings. Precipitation in form of rain and snow in winter, too, enhance tree growth by raising the groundwater level and improving the water supply in the habitat during the subsequent spring. Droughts in spring and summer, coupled with high air temperature, result in narrow rings. The tree-ring width/climate relationships at the two indigenous oak species are very similar to those of downy oak. Responses are, however, more distinct and with a higher statistical significance.