In Allier, central France, oak forests cover more than 60 000 ha and represent an annual wood stock of 11 million m3. This is more than 8% of the annual French production and especially it is about 10% of the annual French production of stavewood, a premium quality wood used for manufacturing barrels worldwide. However, for several years, an oak decline has been observed with economic, ecological and cultural consequences for this territory. In the context of climate change, the models of climatologists announce an increase in the heterogeneity of annual rainfall distribution. This means an increase of winter-spring waterlogging and marked summer droughts. Both of these events are estimated to have a strong impact on the oak decline by limiting tree growth and/or inducting a deficit of carbon reserves that may limit future resistance to stress, especially related to winter frosts. Therefore, our objectives were i) from a scientific point of view, to better understand the role of waterlogging, drought and their interactions on oak decline; and ii) from a practical point of view, to provide manager tools for estimate oak decline risk according to site and climate characteristics. We worked with two main oak species: Quercus robur and Quercus petraea, in order to estimate the specific vulnerability of each species. In the literature Quercus robur is supposed to better resistant to waterlogging and on the contrary Quercus petraea seams to be better drought resistant. Little is known about the effects of alternation of these two stresses on the health of both oak species. Microclimate (light, rainfall, soil and air temperatures, air humidity), soil water balance (volumetric soil water content measured by TDR sensor, water table depth), tree transpiration (estimated by sap fluxes), winter frost resistance (LT50: thermal lyses by electrolyte leakage method) and root and stem growth (rhizotrons, automatic micro-dendrometers) are recorded on two systems: * An experimental one with two years old oaks in containers in the laboratory. Responses of trees are recorded after different controlled alternating conditions of waterlogging and drought, relative to time of application and intensity. * In the field, in eighty years old stands selected on hydromorphic soils in forest in Allier. Because of the high clay content, this characteristic poor soil allows to observe effect of a natural alternation from high levels of superficial water table in winter-spring to marked droughts in summer.