This is an English translation of three papers in French which have been published in scientific journals in 1984, 1985 and 1988. The present document describes the components of a moder humus profile under Scots pine, as they can be observed under a dissecting and a light microscope. Plant litter debris, roots and animal feces were collected over a small area (5 x 5 cm) in order to be sectioned and stained. All animals and microbes (fungi, bacteria, micro-algae) collected within a small area of litter (5 x 5 cm) were identified to the finest possible taxonomic level. Gut contents were analyzed and compared with the composition of the immediate environment in order to have the most reliable view of trophic relationships between plants, animals and microbes living in the same restricted environment.