Seasonal and diurnal variability in sap flow intensity of mature sessile oak (Quercus petraea (Matt.) Liebl.) trees in relation to microclimatic conditions.

In this study sap flow dynamics of mature sessile oak trees (Quercus petraea) in a marginal sessile oakturkey oak forest was investigated in 2009. That year spring was dry without significant rain in April and May and the driest month was August. Due to the extreme weather conditions the volumetric soil water content (SWC) of upper 30 cm was low on experimental days in May (0.13–0.14 cm3 cm−3) but it reached the lowest value in August (0.08 cm3 cm−3). Sap flow was measured in a dominant and a co-dominant tree by heat dissipation method from 26 March till 30 October. In the present paper several three-day long periods of the continuous seasonal recordings were chosen to represent the effects of typical weather conditions and different stages of canopy development on sap flow dynamics. The daily maximum sap flow density values of dominant and co-dominant trees were similar (0.30–0.32 cm3 cm−2 min−1) in moist period (July). Rains and transient increase of SWC after proceeding drought resulted in change of di...