Dendrochronology has been used to date sub-fossil wood excavated from former wetland woods located in Zwolle-Stadshagen, the Netherlands.Tree-ring analysis was performed on oak and ash to gain insight into changes in the growth dynamics of the trees resulting from changes in external site conditions, particularly hydrology. In addition population dynamics of oak and ash were studied by observing the temporal distribution and mean age of the oak and ash trees in the period when the woodland existed. The results showed that woodlands with oak and ash at Zwolle-Stadshagen existed at least for a period of about 700 years, from ca. 150 BC to AD 580 (ca. 2200 -1400 cal. BP). The oak and ash were slowly growing and showed alternating phases of normal and depressed growth. Growth depressions occurred with a frequency of about 20 to 40 years. Almost all of these depressions were synchronous with those in oaks from other -mainly wetland areas -in NW Europe.Consequently, a regional (climate) factor must be considered responsible for this phenomenon. By taking into account the specific growth conditions in wetland woods it is very likely that this factor is linked to site hydrology. Around AD 300 (ca. 1650 cal. BP) a remarkable shift in population dynamics occurred in both oak and ash with many new trees establishing. This indicates a period of striking changes in site hydrology preceding the collapse of the woodland starting around AD 530 (ca. 1420 cal. BP).