Humus functioning types in evergreen coniferous forests of the French Inner Alps.

Three humus forms that are widespread in the Inner Alps, a dysmull below Pi nus sylvestris, an oligomull below Abies alba and a mor below Pinus cembra, were studied by following mineral nitrogen production and uptake and by a characterization of the pedofauna. Due to the production and uptake of nitr ogen, mainly as nitrates and also due to the dominance of Lumbricids versus Arthropods, the oligomull was the sole humus form that functioned as a mul l. Nevertheless relatively weak mineral nitrogen production and the dominan ce of endogeic soil-dwelling earthworms versus anecic earthworms demonstrat ed the moderate activity of this mull, which is representative of humus for ms of old growth forests and cold climates. There was a discrepancy between the very low biological activity of the dysmull and its status of mull, wh ile an observed bifunctioning between the different layers of this humus al so differentiated it from the mor. (C) 2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.