Beyond the concept of dominant soil: Preserving pedodiversity in upscaling soil maps

Most small-scale soil maps report dominant typological units and allow only a partial appraisal of pedodiversity since territories with similar dominant soils can actually possess different pedodiversity. This is particularly true at the national scale, where a great wealth of soil information collected at more detailed scales is generalized. A methodology was set up, which aimed at preserving pedodiversity in upscaling soil maps by using geomatic techniques and the World Reference Base for soil resources (WRB). The main source of information was the soil system geodatabase of Italy, storing information of soil typological units and soilscapes at the 1:500,000 reference scale. Qualitative aggregation of soil taxa followed upscaling rules aimed at (i) maintaining the information about pedogenetic processes and (ii) grouping soilscapes showing recurrent patterns of soil forming processes. The upscaling methodology can be summarized in seven steps as follows: (1) soil forming processes selection, retrieved from soil typological units stored in the national database; (2) upscaling soil systems and creation of broad soil regions at 1:5,000,000 reference scale; (3) semantic upscaling of typological units to form taxa showing different soil forming processes; (4) ranking and associating soil forming processes; (5) geography upscaling of soil systems geometry to form polygons at 1:1,000,000 reference scale, called subregions; (6) ranking subregions according to their extension; (7) naming subregions by ranking the taxa according to the number of soil typological units. The soil subregion map reported 47 map unit and 148 taxa, belonging to 22 reference soil group of WRB and showing from one to four qualifiers. Each map unit had from 2 to 18 taxa, for a total of 317 occurrences. Thirty taxa had 3 or more occurrences, while the remaining took place in one or two subregions only. Diversity indices scored a very high Shannon's H' = 5.35 on an H-max = 5.76 for the whole country. The value of the Evenness index (E) was 0.93. The map of Shannon's H highlighted that the highest pedodiversity in Italy is preserved in the northernmost part of the Alps, in the coastal plains of Central and Southern Italy, and in some hilly lands of Central Italy. On the other hand, large plains of Northern Italy and mountainous areas of the Central and Southern Italy keep low pedodiversity. The comparison of the results with studies on vegetation diversity and land degradation and desertification suggested the existence of linkages between pedodiversity, biodiversity, and the current and past management of agricultural and forest ecosystems. (C) 2015 Elsevier B.V. All rights reserved.