The influence of soil type and interspecific competition on the fine root system of Norway spruce and European beech

Recent knowledge about root systems of trees mostly originates from studies in pure stands. But the root systems may change if more than one species is present. The fine root system (d < 2mm) of spruce was characterized for pure stands and for comparable mixed spruce/beech stands to a soil depth of 80 cm. This made it possible to estimate the effects of interspecific competition on stagnic cambisol and on dystric cambisol, respectively. An additional pure beech stand was studied on stagnic cambisol to evaluate the mixture effect also on the root system of beech. The total fine root biomass was greater in each mixed stand compared to the neighbouring pure stand. Fine roots of beech were over-represented in the rooting zone of the mixed stand, which indicates a competitive displacement of fine roots of spruce. In addition, spruce developed a more superficially distributed root system in the mixed compared to the pure stands. The low abundance of spruce roots in mixed stand and the limitation of spruce roots to the uppermost soil layers underlines the high competitive ability of beech in the rooting zone of the investigated mixed stands.