The purpose of this study was to explain decline in vitality of even-aged oak (Quercus robur and Q. petraea) stand observed in three sites located in the county of Allier (Auvergne, Central France). Our analysis showed that microclimatic variables measured under tree cover (air relative humidity and temperature, rainfall, radiation, and calculated ETP) were very similar among the three sites. Records showed that no root growth occurred during waterlogging period (from January to June) in the three sites, because water excess led to hypoxia (oxygen deficiency) which probably caused a decay of the flooded fraction of the root systems. Waterlogging also affected the period of root active growth, i.e. the first flush of root growth did not occur, when oak normally has two flushes of root growth, one in late June and another in late July. After the water table decrease, root growth was observed in the three sites, but rooting profiles (0-180 cm below ground) were variable in the course of time, this fact is related to soil water content. As the soil surface horizons desiccated, root growth and plant water uptake may preferentially occur in deeper horizons in order to attenuate the duration and intensity of water deficit. These deep fine roots probably acted only during a short period (end of summer), when oxygen supply was sufficient, i.e., when water table fell. However, water deficit was strongest in one site, this fact may be due to its soil type, podzolic pseudogley, susceptible to dry out quickly and strongly in summer due to the coarser texture: the maximum water reserve is particularly low. Therefore, we can conclude than the root growth has two main issues in a one-year cycle. One is the temporary ground water table which stops the growth of the new roots during the waterlogging period, and the second issue is a low soil water content that becomes the main water limit for well root growth in a drought period.