Patterns of soil water depletion under coexisting oak and beech trees in a mixed stand

Soil moisture regimes were studied under two European beech trees (Fagus sy(lvatica L.) and two Durmast oak trees (Quercus petraea (Matt.) Liebl.) in a mixed oakbeech stand on the Luneburger Heide, NW Germany. In the long run, oak is out-competed by beech in this stand. Water is among the factors that might influence competitive interaction between beech and oak. In the growing seasons 1990, 1991 and 1992, soil water matric potential was monitored with a large number of tensiometers which were installed at six soil depths and within four distances from the stem under the four trees. Troughfall and stemflow were recorded separately under the canopies of the two species. Overall patterns of matric potential fluctuations were similar under both oak and beech