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L. Goaster, 50-70 cm) Soils in S40 were sampled in March 1991 lIsing the same sampling scheme, but only three replicate samples \Vere taken at each plot Sampling plots in S40 \Vere chosen in areas where trees had not been clamaged by winclthrow The five (S90) or tbree (S40) replicates of mineraI soil col!ected at each plot were blllked in the field Litter ancl soil samples were air-dried, weighecl, sievecl, ancl the COal'se fraction (>2 mm) was weighecl. Soils were resampled at both sites in January 1996, and soils from S90 (0-10,10-30 ancl30-50 cm) were samplecl again in Exchangeable Ca 2 +, Mg 2 +, Mn 2 +, A1 3 + and H+ were extracted from ail soil samples in 1996 using 1 M KCI; extract concentrations ofCa 2 +, Mg 2 +, Mn 2 + ancl A1 3 + were analyzed by inductively couplecl plasma emission spectrometry (lCP) Al J + ancl H+ were determined by titration (Espiau ancl Peyronnel, 1976) Exchangeable K+ was displacecl by 1 M NH 4 Cl using the same procedure ancl analyzed by ICP Cation exchange capacity was ca1cu1ated by summing up exchangeable cations. For each soillayer, significant changes in exchangeable cations between 1990/91 and 1996 were checked by pairwise comparisons using Student's t test. The annual increment ofnutrients in biomass was determined in 1988 after a biomass and mineraI content inventory Mineralogical investigations were conductecl on a representative soil profile to determine the quantitative mineralogy of the different partic1e size fractions Present weathering rate was calculatecl with the geochemical moclel PROFILE (Sverdrup and Warfvinge, 1988), using mineralogical ancl chemical data from the site The historical weathering rate also was calculated using isotitanium and isoquartz balances and divicling soillosses in base cations by 10,000 yr, i.e. the approximate age of the soil. 3. Results 3.l. SOIL EXCHANG EABLE CATIONS No significant change in the mass of L + F horizons was measured between 1990/91 ancl 1996 at either site Exchangeable Ca 2 + concentrations clecreased significantly only in the 10-30 cm layer, whereas exchangeable K+ concentrations decreased significantly in the 10-30 cm and 50-70 cm layers, S90 were sampled at five plots. At each plot (15 x 15 m) , we sampled five replicates of the Iitter layer At S90, except in the 0-10 cm layer, exchangeable Ca 2 + and Mg 2 + concentrations were statistically lowerTable II). Exchangeable Mn 2 + concentrations decreased in ail layers, but changes in exchangeable Ae+ and K+ concentrations were not significant. At S40, exchangeable Mg 2 + concentrations decreased significantly below 10 cm clepth Exchangeable A1 3 + concentrations decreasecl significantly in the 30-50 cm layer. Concentrations of exchangeable Ca 2 + and Mg 2 + at S90 were lower in March than in Total amounts in exchangeable base cations in the top 70 cm of mineraI soi1 were significantly lower (p < 0.05) in 1996 th an, 1990.

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