Cycle de la matière organique et gestion des bioéléments dans un peuplement de hêtre (Fagus sylvatica L.) de l’Etna

Abstract

A beech (Fagus sylvatica L.) forest stand, with 2125 stems per hectare, from the highest part of the Etna volcano (Sicily) was estimated, from representative samples of whole trees, as having an above-ground biomass of 132 Mg ha-1 (128 Mg ha-1 woody material ; 4 Mg ha-1 leaves). Corresponding root biomass has been estimated at 25 Mg ha-1, according to the observations of other authors. Above-ground biomass included 327 kg ha-1 of calcium, 141 of potassium, 94 of nitrogen and 35, 27, 8 and 2 kg ha-1 of magnesium, phosphorus, iron and manganese respectively. Yearly increment of above-ground perennial biomass amounted to 7.9 Mg ha-1, immobilizing 20 kg ha-1 year-1 of Ca, 7 of K, 4 of N and respectively 2, 1, 0.5 and 0.2 kg ha-1 year-1 for the other 4 nutrients studied. Litter-fail amounted to 3.9 Mg ha-1 year-1, with 3.5 Mg ha-1 being leaf-litter. Contained within litter-fall, 33 kg ha-1 year-1 of Ca, 20 and 19 of N and K, 5, 4, 1 and 0.1 kg ha-1 year-1 of Mg, P, Fe and Mn are returned to the soil each year. Above-ground litter layer amounted to 13 Mg ha-1, including 20, 7, 4, 2, 1, 0.5 and 1 kg ha-1 of Ca, K, N, Mg, P, Fe and Mn respectively. If the amounts of the various compartments, and the fluxes of organic matter and nutrients are very close to those determined for other even-aged Fagus sylvatica L. stands elsewhere in Europe, nitrogen contents are comparatively very low. This probably results from the low nitrogen availability in the soils of the Etna volcano.