Strontium isotope composition as a tracer of calcium sources in two forest ecosystems in Belgium

Our results emphasize the importance of the atmospheric contribution of Ca for tree mineral nutrition in the studied forest stands, suggesting that these ecosystems on acid soils are sensitive to chemical changes in the atmospheric environment, e.g. acid depositions associated with decreasing input of atmospheric cations. Our results support therefore the conclusion of Hedin et al. [Hedin, L.O., Granat, L., Likens, G.E., Bulshand, T.A., Galloway, J.N., Butler, T., Rodhe, H., 1994. Steep declines in atmospheric base cations in regions of Europe and North America. Nature, 367: 351-354], suggesting that the atmospheric base cation trends in Europe and North America are ecologically relevant on the scale of decades for poorly buffered ecosystems. This is a serious possibility of depletion of the soil available cation pool of the High Belgium beech forest, which grows on a bedrock with extremely low levels of total calcium.