Daily and seasonal variation of stem radius in oak

Seasonal and diurnal variation of stem radius and sap flow in large pedunculate oaks (Quercus robur L.) as dependent on environmental factors was studied in the floodplain forest in southern Moravia from April to October several years after cessation of regular natural floods. Two main processes as driving variables of stem radius were considered separately: growth of plant tissues and their hydration (i.e. shrinking and swelling). Different types of diurnal dynamics of stem radius occurred including growth with and without shrinkage, growth at night and shrinkage during daytime and vice versa. A simple physiological model was applied to describe the dynamics of stem radius. Data on sap flow, global radiation and air temperature were used as model input. Net growth was simulated by means of photosynthesis and respiration, calculated for real meteorological conditions and tissue hydration was derived from the difference between potential and real transpiration (sap flow). Simulation showed good approximation of seasonal dynamics of stem radius by the model under mild weather conditions and mostly non-limiting soil moisture. © 1999