EARTHWORM FAUNA IN THE FORESTS OF THE CANTON ZURICH (SWITZERLAND)

Thirteen earthworm species were found in 7 plots in the forests of the canton Zurich. Six plots contained areas of beech and spruce, the seventh only spruce. The number of species varied from 3 to 7 in beech areas and from 1 to 8 in spruce areas. Generally, fewer species were found in the spruce areas. High earthworm biomasses were caused by a high abundance of the species Lumbricus terrestris L. and Nicodrilus nocturnus (Evans). Theoretically, in the Zurichberg (beech and spruce) and Winterthur (beech) plots earthworms (biomasses per m2 > 75g) may utilise all the annual litter, and in the Gubrist (spruce) plot (biomass per m2 = 30 g) the majority of the annual litter fall. As a consequence of the small number of plots, it was not possible to make inferences with regard to the dependency of biomass and species diversity on environmental factors, such as soil pH, mean annual temperature, humusform, amount of annual litter fall and soil textural class. It is confirmed that at present earthworms are only of limited value as bioindicators in forests, since the factors determining their distribution are not fully understood.