Long-term study of formerly litter-raked Scots Pine ecosystems in NE Bavaria: Recent changes in soil chemical properties and stand nutrition

For two sites in NE Bavaria (Germany) forested with mature stands of Scots Pine (Pinus sylvestris L.) characterized by acidic soils derived from acidic parent material (phyllite-Pfaffenwinkel, and cretaceous sediments-Pustert) and substantial devastation due to intense litter-raking in the past, recent changes in the chemical status of the topsoil (acidification, N eutrophication) and in the nutritional status of the pine stands were investigated. Changes in topsoil chemistry were quantified by comparing the results of soil inventories carried out in 1974, 1982/1984, and 1994. Changes in the nutrition of the forest stands were assessed by repeated analyses of half-year old needles conducted at least every second year from 1964 to 1994. For both sires, a considerable acidification of the topsoil horizons was noticed. The pH value decreased significantly between 0.1 to 0.2 units (all horizons of Pfaffenwinkel, O layer of Pustert) and about 0.3 to 0.4 units (mineral soil of Pustert). Additionally, we found a significant decrease in base saturation and in the amounts of exchangeable Ca (only for Pustert) and Mg (both sires) in the topsoil. Only in the O layer of Pfaffenwinkel the C/N ratio decreased slightly between 1982/84 and 1994, whereas the C/N ratio of all other studied horizons remained constant or increased. The nutritional scarus of the Scots Pine stands on both sires changed in a similar way. In contrasting to the situation in the early 1960ies, the N deficiency dissappeared and needle growth increased dramatically in the course of the monitoring period. Both, the average weight and the N levels of half-year old needles increased significantly within 20 years for 25 by 33%, and 13 by 18%, respectively. On the other hand, the Ca concentrations decreased from 16 to 27%. K and P showed only minor, insignificant changes; the Mg concentrations developed differently at both sites. For Pfaffenwinkel, an increasing risk of Ca shortage particularly in warm and dry years is postulated, if the observed trend of a decreasing pool of plant-available Ct in the topsoil continues in the future.