Germination of acorns and development of oak seedlings (Quercus robur L.) following flooding

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.