Altitudinal variability of the soil water content in natural and managed beech [Fagus sylvatica L.] forests

European beech (Fagus sylvatica L.) ranks as one of the most adaptive species among European indigenous trees. Variable interactions between the trees and soil water depend on both phenotypic plasticity of the species and natural conditions. They are controlled through stomatal regulation and the ability of beech trees to accelerate quickly their growth if available resources increase. However, the effect of forest density at various altitudes on the soil water content in beech stands has been studied rather scarcely. Therefore, we monitored soil moisture by means of Time Domain Reflectometry in series of natural and managed stands located on sites representing the lower altitude (200–550 m a.s.l.), middle altitude (550–1050 m a.s.l.) and higher altitude (1050–1300 m a.s.l.) zones of the natural beech belt in the Western Carpathians, Slovakia. Forest stand density, expressed in terms of basal area, i.e. the sum of cross section areas of the tree stems at 1.30 m height, was unchanged in natural stands, but it was reduced by 60% in the shelterwood stands. In the clear-cuts, all trees were removed. Total soil water content (SWC) under forest stands was calculated in mm as the product of soil moisture and soil depth, the latter acquired by electrical resistivity tomography. SWC differences between natural and shelterwood stands of the lower altitude, middle altitude and higher altitude zones averaged 18 mm, 36 mm and –3 mm, respectively. According to the Friedman test on ranks, followed by post-hoc multiple comparison testing, the difference was only significant within the middle altitude zone. In it, soil water consumption by the natural stand was limited only by the hormonally controlled seasonal regulation. The comparatively low water loss in the shelterwood stand resulted from a small rainfall interception by forest canopy and a decreased soil water uptake due to reduced basal area, leaf area index and simple age-size forest structure. In the lower altitude zone, the precipitation deficit and limited extractability of soil water were responsible for the absence of larger SWC differences. As opposed to that, low potential evapotranspiration prevented any noticeable SWC differences within the higher altitude zone.