Seeds and seedlings of Quercus robur, a characteristic tree species of the hardwood floodplain forests along the Rhine River, demonstrated high resistance to complete inundation under controlled conditions. In both experimental trials no significant difference between the different flooding periods (8, 10, and 12 weeks) could be established either for shoot emergence or for the measured morphological growth parameters. Flooding delayed the germination of submerged acorns till the end of inundation. However, seeds of the flooding treatments had significantly higher germination rates than the non-flooded acorns of the control. Likewise, dry weights of seedlings from the flooded seeds were significantly higher than those of seedlings from seeds not flooded. Aboveground growth in the 24-week growth period following flooding was reduced in favour of root development in either trial of the experiment. Restricted leaf development and reduced shoot elongation stalled the growth of young oaks in the seedling trial. The results confirm knowledge from earlier experiments about the flood tolerance of Quercus robur seed and seedlings. They also serve to explain why oak seedlings are widespread on the Rhine floodplain after mast years, but gradually disappear in successive years.Keywords: inundation; experiment; mortality; morphology; recovery; pedunculate oak 392 J. FOR. SCI., 53, 2007 (9): [391][392][393][394][395][396][397][398][399] Quercus robur revealed the least damage out of the six tested broadleaf tree species, demonstrating the best adaptation to flooding stress.In spring 1999, the meeting of flood waters from the Rhine and many of its tributaries along the upper part of the stream resulted in the worst flood of the last century. The extreme rise in the water level was caused by unusually mild and wet weather in the northern Alps. In the course of this event Kühne et al. (2005) observed high mortality and growth inhibition of Quercus robur grown from direct seeding and nursery plants at study sites situated between Speyer and Karlsruhe (Germany). In the experiment presented in this paper flood conditions of 1999 were simulated when acorns and seedlings from Quercus robur were entirely submerged under controlled conditions in growth chambers and germination of seeds and regeneration capacity of seedlings following flooding were investigated. Based upon field observations the following hypotheses were tested in this work: -Seeds begin to germinate only after flooding.-Germination rate decreases as the duration of inundation increases. -Inundation during the vegetation period results in leaf abscission and necrosis of the shoot. -Mortality of seedlings increases as the duration of inundation increases. MATERIAL AND METHODS SeedsSeeds were collected in a single-layered mature Quercus robur stand in southern Rhineland-Palatinate (Bellheim Forest District, Germany) in October 1999. The stand is subjected to annual floods from the Rhine River. Seeds were stored at 4°C until sowing. Prior to the commencement of t...