Observed on a 5 x 5 cm small surface of litter in a 35-years-old Scots pine stand with bracken and the moss Pseudoscleropodium purum, the Fl layer is extensively invaded by a mycelial mat made of several mycorrhizal fungi. Observations under a light microscope gave circumstantial evidence of the role of these fungi in advanced stages of decomposition: they seem to protect the partly decayed plant material and the faeces deposited by soil animaIs from subsequent attack by soil bacteria. Penetration of pine needles and cadavers of soil arthropods is prominent in so far as animaIs have previously made entries by tunnelling into the substrates. In addition the black mycorrhizal fungus Cenococcum geophilum was observed to penetrate bracken epidermal cells by its own means and to make lysis zones in dead arthropod cuticles. Consequences for forest soil ecology and tree nutrition are discussed in view of existing literature.