Before industrialization low-base saturation in podsols in mid-Europe, that had developed in the post-glacial period, was restricted to the A-horizon, while the subsoils had intermediate base saturation. In the 1920s the pH value of B horizons of soils in sheltered areas in north Germany was mainly above 5.0. Even in the 1950s most montane beech and coniferous forests of Germany had a base saturation above 20% and 30% (Ulrich, 1986; Ulrich and Meyer, 1987; Hartmann and Jahn, 1967).

   The most convincing evidence that soils have been progressively acidified during the past 20-30 years has been presented by Hallbäcken and Tamm(1986), in which study the soil pH of identical soil profiles was measured in 1927 and 1983. Together with the soil pH measurements of Falkengren-Grerup (1986) and the soil chemical analyses of Ulrich et al. (1989), it emerges (Fig. 5.1), that the main change in soil chemistry occurred after 1960. The Ca/Al or Mg/Al ratios in soil solutions decreased in parallel with the change in pH. Presently more than half of the forest soils in northern Germany exhibit a base saturation of exchangeable Ca and Mg below 10% (Ulrich, 1987).