Base Cation Supply in Spruce and Beech Ecosystems of the Strengbach Catchment (Vosges Mountains, N-E France)

In spruce and beech stands, mineral budgets for a rotation period were calculated from measured element fluxes. The release of base cations by mineral weathering was calculated with the steady state soil chemistry model PROFILE. The calcium release rate by weathering of the mineral fine earth was extremely low. For the period of one rotation, mineral weathering cannot provide enough Ca to compensate timber harvesting and leaching. Forest sustainability depends strongly on the amounts of Ca gained from deposition and lost by biomass removal. Magnesium was supplied by atmospheric deposition and mineral weathering. Calculated weathering rates were close to present soil losses. However, as the model assumes that all dissolution reactions are congruent, the computed release rate of Mg from illite might be too high. Main inputs of K to the soil solutions were primarily attributed to canopy leaching and litterfall in upper horizons and to mineral weathering in deeper horizons. The cation budget of the beech stand was much more equilibrated than that of the spruce stand. Given possible changes in silviculture and deposition chemistry, the sustainability of the present stands is rather improbable with respect to their mineral supply.