ABSTRACT
Little is known about below-ground competition between different tree species in mixed forests. We investigated the evidence for asymmetric competition between fine roots (<2 mm) of adult European beech (Fagus sylvatica) and sessile oak (Quercus petraea) trees in a mixed temperate beech-oak forest by (1) conducting fine-root growth experiments in the field (root chamber technique), (2) comparing the fine-root mass of two-species and monospecific plots, and (3) analysing the density and overlap of beech and oak root systems in shared soil volumes. Field experiments with root chambers, which allow fine-root endings to grow under controlled conditions for several months, showed that beech grew more rapidly than oak roots when both species were grown together. In the mixed beech-oak wood, where stem densities and leaf areas of the two species were similar, beech outnumbered oak three- to five-fold in fine-root biomass, and root tip and ectomycorrhiza numbers, which led to a much greater root:shoot ratio (root area index:leaf area index, RAI:LAI) for beech (3.9) than oak (1.7). The remarkably small fine-root biomass of oak was attributed to competitive replacement by beech roots as indicated by comparison with monospecific oak wood. Although oak had much less fine-root mass than beech, oak outnumbered beech in the coarse root fraction (2
