Radial growth of pedunculate oak and European ash on active river terraces. Hydrologic and climatic controls

The aim of this study was (1) to assess relationships binding hydroclimatic factors and radial growth of pedunculate oak and European ash growing on active terraces of river valleys; (2) to compare the growth reaction of these species from this location. Research site was located in a floodplain valley, within mid-course of the lowland section of the Warta River in the Lasy Czeszewskie Forest, Poland. The Warta River (length 808 km, basin area: 54,529 km2 ) is a mid-size European river, a tributary of the Odra River draining the North European Plain to the Baltic Sea. The sampled forest stand was an old growth composed of pedunculate oak and European ash mixed with other mature tree species. The main conclusions are: (1) ash in comparison to oak growing on the same site located on floodplains appeared to be both more sensitive to hydroclimatical features and less ecologically flexible as far as monthly pattern of water requirements is concerned, therefore adaptation to changing climatic conditions and drought may be a greater ecological challenge for ash than for oak in river valleys; (2) streamflow could be considered as the parameter that substituted precipitation well, or even was more important than precipitation, as far as availability of water for development of tree rings of ash and oak growing on active terraces of river valleys is concerned; however, the role of streamflow in radial growth developing decreased substantially during 20th century; (3) Standardized Precipitation Evapotranspiration Index (SPEI) as a measure of drought is a prospective parameter in dendroecological analysis, since it conveys real availability of water for trees.