Preliminary Mapping and Characterisation of Soils in the Pirin Mountains (Bulgaria)

Soft types, humus types and vegetation as well as their hypsometric variation were analysed in terms of sequences in the northern part of the high mountains of the Pirin National Park at altitudes between 1000 and 2400 m a.s.l. The study area is characterised by a large variety of natural parameters like petrology (mainly marble and granite), morphology (different slope deposits, exposition) and the orographic climate gradient. Statistical analyses using these parameters provided a basis for the soil group classification of the sites. Based on a Digital Terrain Model (DTM) and a geological map of the Pirin National Park, the results of these statistical analyses were used to generate a "map of potential soft groups" (regionalisation using GIS). Six potential soil groups could be determined. The resulting map exhibits a confidence level of 68% on 74.4% of the covered area. Rendzic Leptosols, in combination with Folio Histosols and Histi-lithic Leptosols occur in the alpine and subalpine regions on calcareous substrates. With decreasing altitude they are replaced by a mosaic of Rendzic Leptosols, Phaeozems and an increasing occurrence of Cambic Umbrisols. Umbrisols found on silicatic substrates in the alpine region are replaced by Cambic Umbrisols with decreasing altitude as well. Hence, pedogenesis is characterised by increasing browning and depth of the soil profiles with decreasing altitude. The pH-level is slightly acidic to neutral in lower zones and on calcareous rocky bases. Acidification increases in the subalpine zone. Soft pH decreases down to 4 on silicate subtrates. Typical humic values in mineral topsoils are 10 to 12%, and in organic layers of the softs above 2000 m a.s.l, they are even more. The C:N ratio closely ranges around 20 (median).