LONG-TERM CHANGES OF BASE CATION POOLS IN SOIL AND BIOMASS IN A BEECH AND A SPRUCE FOREST OF SOUTHERN SWEDEN

During the past 60 years there has been a considerable decline in pH in mineral soil beneath spruce and beech stands at Tonnersjoheden Experimental Forest in south-west Sweden. In this report an attempt is made to estimate the corresponding declines in base cation pools. The exchangeable storage of Na, K, Ca and Mg in soil, down to 70 cm depth, is calculated to have decreased by 57-60 per cent for beech and by 56-74 per cent for the spruce stands during the period 1927-1984. The calculated cation depletions are compared with estimated nutrient uptake in biomass, base cation release by weathering and leaching losses due to percolation of strong mineral acids and organic anions during the period. The biological acidification may explain about 50-60 per cent of the total losses of base cations from soil, the cation accumulation in biomass then explain 41-43 per cent units for beech and 34-45 per cent units for spruce. The estimated losses of base cations due to acid rain correspond to an amount of cations similar to that accumulated in the spruce biomass during one generation.