Water balance of a Southern Moravian floodplain forest under natural and modified soil water regimes and its ecological consequences

Abstract

Stand water balance was calculated in a floodplain forest in Southern Moravia. A model was applied to actual and theoretical scenarios of climate and soil water supply. Rooted and root-free soil volumes were considered separately because root development was poor for these trees. Input data, i.e., measured flows within the system including sap flow rate, characterize both the period of regular natural floods and period when floods were interrupted for over 20 years because of canalization of rivers in the region. Under non-limiting underground water supply, net precipitation supplied only about 50 and 25% of water for actual evapotranspiration, ET, under mild and dry weather, respectively, and the other 30 and 60% came from underground sources. The model also characterizes the theoretical situation of no underground water supply, when ET may decrease significantly. An important limit for water supply to the trees may be the maximum hydraulic conductivity K, allowing horizontal transport in heavy soils, because a small decrease in soil water content (2 to 4%vol) causes a large drop in K. K may become supply-limiting before soil water potential becomes a limiting factor. Trees with smaller or damaged root systems or lower root/shoot ratio were especially threatened by drought even on relatively moist heavy soils.