Effects of vegetation type on the biogeochemistry of small catchments (Mont Lozere, France)

Abstract Input-output budgets are presented for three granitic catchments, with contrasting vegetation types (Spruce, Beech and grassland), for the Mont Lozere region of France. Budget results are compared with information for analogous catchments with varying atmospheric pollution loading. Comparisons show relatively small losses of cations and marked sulphate retention in the soils (particularly for the beech and grassland sites) of the Mont Lozere catchments. Retention of sulphate may be underestimated, particularly for the spruce site, owing to occult and dry deposition inputs which have not been measured. Specific effects of the vegetation type upon the soil dynamics and the biological functioning of the ecosystem are described. Losses of the base cations are least significant for the beech forest, and this is linked to low bicarbonate production coupled with high sulphate retention in the soil. The spruce afforestation programme has led to a marked cation-loss increase although the streams have yet to acidify. Deforestation leads to further cation losses in relation to increased nitrate leaching. The biogeochemical functioning of the Mont Lozere ecosystems, although slightly disturbed, is not in steady state; sulphate is still accumulating and the effects of afforestation and harvesting are marked.