Lumbricus terrestris L. distribution within an experimental humus mosaic in a mountain spruce forest

An experiment was designed at a mountain site to study the distribution of adult Lumbricus terrestris in relation to a small-scale mosaic of humus for ms representative of different stages of a spruce forest ecosystem. Good ag reement was found between distribution in the mosaic and that in the field. ANOVA tests demonstrated the strong influence of humus form on earthworm a bundance when comparing a vermimull (high earthworm burrowing activity) tak en from a spruce regeneration site (61.8 individuals m(-2)) with a leptomod er (no earthworm burrowing activity) taken from a 60-year-old spruce stand (6.2 individuals m(-2)). Other humus forms were intermediate (mean density 34.6 individuals m(-2)). The same pattern was found with individual biomass , but with lower significance. Main differences observed in the experimenta l design were attributed to the immediate carrying density of the humus for ms. A distinction was made between humus profiles built up with or without spruce cover. In the latter case (regeneration site and bilberry heath), th e immediate carrying capacity indicated by the experimental approach overes timated the field density by a factor of 4. Under spruce this overestimate was even higher (approximately 10 times too high in an adult spruce stand ( 160 years old) and 30 times too high under moss cover). The increase in den sity due to experimental conditions was not determined for leptomoder humus accumulated under the actively growing spruce stand (160 years old) since the earthworm density was near zero in both cases. Relationships between hu mus form and earthworm populations are discussed.