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1 Geoderma 192 (2013) Contents lists available at SciVerse ScienceDirect Geoderma journal homepage: Soil geography and diversity of the European biogeographical regions J.J. Ibáñez a, J.A. Zinck b, C. Dazzi c, a Centro de Investigaciones sobre Desertificación: CIDE (CSIC, Universitat de Valencia, Generalitat Valenciana), Carretera Moncada-Náquera, Km 4,5 Apartado Oficial 46113, Moncada, Valencia, Spain b Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, P.O. Box 6, 7500 AA Enschede, The Netherlands c Dipartimento dei Sistemi AgroAmbientali, Facoltà di Agraria; Università di Palermo, Viale delle Scienze, Palermo (I), Italy article info abstract Article history: Received 7 January 2012 Received in revised form 25 July 2012 Accepted 29 July 2012 Available online 17 November 2012 Keywords: Europe Soil geography Pedodiversity Biogeographical regions Soil minorities Soil endemisms For decades, soil geography has been mainly a qualitative and descriptive discipline. There are now technologies and mathematical tools available that allow formalizing soil geography in more quantitative terms. In this paper, the distribution and diversity of the soils of Europe are analyzed using GIS tools and pedodiversity algorithms. Soil data were taken from the European Soil Database (V2.0) and computed within the spatial framework of the Biogeographical Regions of Europe (BGRE) as defined by the European Environmental Agency (EEA) on the basis of climate and vegetation. The results obtained show the soil assemblages, including dominant soils and endemic and non-endemic soil minorities, and their respective soil diversity for each BGRE. Most BGRE have dominant soils that mainly reflect the influence of the climatic conditions prevailing in each regional context. Although the definition of the BGRE lacks relevant information on geology, relief and paleogeographic evolution, soil assemblages of most biogeographical regions are idiosyncratic and characterize quite well the European soilscapes. Northern BGRE (i.e. Arctic and Boreal) have low pedotaxa diversity in contrast to the other BGRE. The mountain biome has the highest pedorichness at European as well as at global level. The Atlantic and Mediterranean regions and, to some extent, the Alpine region are mutually related. Most continental soilscapes constitute a mix of typical steppe and forest soils. The Black Sea region, the smallest one of all, has no idiosyncratic soil type, suggesting that it could be considered as an important biodiversity hotspot rather than a genuine biogeographical region. These results are relevant as baseline information for a full inventory of pedodiversity and as an important part of the European natural heritage Elsevier B.V. All rights reserved. 1. Introduction The European soil geography has been studied for decades from different points of view, at different scales, and making use of different national classification schemes (Jones et al., 2005) as well as the FAO Keys (1974, 1990) and, more recently, the WRB framework (FAO, 1998, 2006). However, a comprehensive, quantitative analysis of the spatial distribution of the soil types (pedotaxa) across the continent is still lacking, whereas a digitized georeferenced soil database at European level permits now to undertake such an analysis. A first initiative was carried out for the European Communities (CEC, 1985), resulting in the publication of a soil map in paper format for most of the western countries. This map was subsequently digitized, improved, and expanded several times until the latest 2004 version on CD-ROM (EC, 2004). Likewise, a Soil Atlas of Europe (ESBN-EC, 2005) together with a monograph on Soils of European Union (Tóth et al., 2008) has been published recently. This is mainly descriptive information. Several papers provide a more elaborate vision on the spatial distribution of the soil types across Europe, showing fractal structures at least Corresponding author. Tel.: ; fax: addresses: choloibanez@hotmail.com (J.J. Ibáñez), zincka@itc.nl (J.A. Zinck), carmelo.dazzi@unipa.it (C. Dazzi). for the most abundant pedotaxa (Ibáñez et al., 2009). Pedodiversity analysis has been considered to be an interesting mathematical tool in soil geography (e.g. Ibáñez and Effland, 2011), and soil geography is increasingly formalized in quantitative terms (Gray et al., 2011; Ibáñez et al., 1998). Pedodiversity analysis has been used at worldwide level (Ibáñez et al., 1998; Minasny et al., 2010) and in the United States of America (Amundson et al., 2003; Guo et al., 2003), but it was not yet applied to the European continent. The objective of this paper is to show the soil assemblages of most European countries and analyze their pedodiversities in a quantitative way. The paper intends to match the primary data contained in two complementary documents, the Soil Atlas of Europe (European Soil Database) and the Map of the Biogeographical Regions of Europe, to generate integrated information describing the soil geography and soilscapes of the European continent and analyzing the factors that explain the pedodiversity in the frame of the biogeographical regions. 2. Material and methods 2.1. Material To analyze soil geography and pedodiversity of Europe, the continent can be fragmented using different geometric supports such as /$ see front matter 2012 Elsevier B.V. All rights reserved.

2 J.J. Ibáñez et al. / Geoderma 192 (2013) Fig. 1. Biogeographical Regions of Europe.

3 144 J.J. Ibáñez et al. / Geoderma 192 (2013) administrative boundaries, drainage basins, or biogeographical ecological units. Both the country borders and the drainage basins often cross several environmental units, making it difficult to compare the spatial distribution of pedotaxa and soil forming factors. In view of the former, this paper uses the official version of the European map of biogeographical regions (BGRE) at the scale of 1:1 M (EEA, 2002), excluding associated areas that do not belong to the physical geography of Europe such as the Anatolian Biogeographical Region, also excluded in its last version (EEA, 2008) (see open access link in the reference list). The definition and delineation of the BGRE are mainly based on climate and vegetation, but geologic and geomorphic criteria, together with land use histories, were also taken into account for differentiation. Therefore, the BGRE (Fig. 1) can be used as spatial frameworks for the analysis of soil geography and pedodiversity across the European continent Procedures using GIS software The European Soil Database (V2.0) (EC, 2004) and the related digital soil map at the scale of 1:1 M were used to show the distribution of the soil types and miscellaneous units (see open access link in the reference list). The European Soil Database collects the information provided by national soil data centers, which work with different national classification systems and at different surveying scales. Thus, because of the small scale of the maps and cartographic generalizations, the pedotaxa inventory might be incomplete for some of the countries. The soil classification was according to the 1998 version of the World Reference Base for Soil Resources (FAO, 1998) that consists of 30 units at the first level and 531 units at the second level. Europe contains 26 and 134 soil units respectively, plus six miscellaneous units as indicators of non-soil covers that differ in each BGRE (man made soils, rock outcrops, lagoons, water bodies, glaciers, and sealed urban areas). In the present study, the soil units are termed pedotaxa of the first level and second level of the WRB, respectively. The soil maps were drawn in the Lambert Azimuthal Equal-Area projection with longitude of origin 20 E and latitude of origin 50 N. Equal-area projections are best suited for area distribution maps. The GIS softwares Geomedia Professional (V6.0) and Geomedia GRID (V6.0) were used for data handling. The distribution maps of the pedotaxa at the first and second levels were obtained following the steps described by Ibáñez et al. (2009). This was achieved by disaggregating the soil map associations (EC, 2004) into their constitutive pedotaxa, obtaining 30 and 140 vector maps with soil polygons and miscellaneous units respectively for the first and second WRB levels. These maps were subsequently rasterized with a cell resolution of 25 km 2 (i.e. the smallest soil polygon delineation). The technical procedure of vector raster conversion is described by Benito and Suárez (2005). The total extent covered by each pedotaxum at the first and second levels in the European Soil Database was split and areal proportions were recalculated per biogeographical region of occurrence (i.e. Alpine, Arctic, Atlantic, Black Sea, Boreal, Continental, Macaronesian, Mediterranean, Pannonian, and Steppic). Additional information on the Macaronesian biogeographical region at the first level of the WRB, which was not recorded in the European Soil Database, was also included (Benito and Suárez, 2005) Estimation of pedodiversity A pedodiversity analysis was carried out for the soil assemblages of each BGRE using the following indices: richness, Shannon diversity index, and Shannon evenness (Shannon and Weaver, 1949). A friendly discussion of pros and cons of these indices can be found in Magurran (1988). Richness(S) refers to the number of pedotaxa occurring in a given BGRE. The Shannon Index (H ) is the most commonly used diversity index in ecology and pedology (Ibáñez et al., 1990, 1995; Shannon and Weaver, 1949): H 0 ¼ i¼n i¼1p i lnp i where p i is estimated by means of n i /N where n i is the area covered by the ith pedotaxum, and N the total area of each BGRE. Any logarithmic base can be adopted to calculate Shannon's Index. The natural logarithm was used in this article. Thus, the value of H is the sum of the areal proportions covered by a pedotaxum in a given BGRE multiplied by the negative logarithm of the total proportion occupied in the same BGRE. It ranges from 0 (ln 1) in the case a single pedotaxum covers the total area of a BGRE (richness=1), to ln S in the case all pedotaxa cover similar extents in a BGRE. This index is a measure of information on a group of objects (species, soil types, etc.) which have different probabilities of being represented. Maximum information occurs when the probabilities (proportional abundance) of all pedotaxa are the same. It is then equal to ln S. Information is 0 if there is only one possibility, meaning that one pedotaxum covers the 100% of a hypothetical BGRE, i.e. diversity is 0. The relationship between the observed value of H and its maximum value H max (for a given richness) occurs when the area covered by all pedotaxa is equiprobable in a given BGRE. This is used as a measure of evenness or equitability (E): E ¼ H 0 =H max ¼ H 0 =ln S where S is the richness or number of classes and E takes values in the interval (0, 1). E refers to the relative abundance (i.e. evenness or equitability) of pedotaxa and is the most common index used as a measure of structural heterogeneity Definition of endemic soils and soil minorities The analysis highlights the distribution of the dominant soils but it also shows the occurrence of soil minorities and soil endemism per BGRE. The concept of soil endemism is a promising one for identifying rare, unique, and endangered soils (Bockheim, 2005). Likewise, Goryachkin (2004) used the term soil minorities more or less for the same purpose. In this paper, soil minorities refer to pedotaxa that cover less than 25,000 km 2 at European level. There are 45 soil types of this kind at the second WRB level. The areas covered by pedotaxa in the European continent follow the termed Willis curve (Ibáñez et al., 2005a,b), meaning that many soil types cover small areas within each BGRE, while only a few cover large extents. Several soil minority types can be distinguished such as follows: (1) endemic biogeographical pedotaxa are those soil minorities that only appear in one single BGRE; (2) endemic geographical pedotaxa correspond to soil types that appear in small areas but cross the boundaries of two contiguous BGRE, indicating that factors other than the bioclimate may explain soil cluster overlapping, such as paleogeographic evolution, geological structure, and/or land use histories; (3) disjoint soil minorities are soil types of small surface areas occurring in two or three geographically separate clusters, as well as in more than a single BGRE; and (4) relatively dispersed or widespread soil minorities are pedotaxa that appear in different BGRE and are widely distributed over the continent, reflecting possibly specific combinations of soil forming factors that repeat at larger scale. 3. Results: the biogeographical regions and their soil assemblages Table 1 lists the 32 pedotaxa and miscellaneous units at the first WRB level per BGRE, while Table 2 lists the 140 pedotaxa and ð1þ ð2þ

4 J.J. Ibáñez et al. / Geoderma 192 (2013) Table 1 Soil assemblages at the first level of the WRB (FAO, 1998) in areal percentages of each BGRE. Pedotaxa Alpine Arctic Boreal Atlantic Mediterranean Continental Pannonian Black Sea Steppic Macaronesian Albeluvisols Acrisols Alisols Andosols Arenosols Anthrosols Chernozems Calcisols Cambisols Cryosols Fluvisols Ferralsols Gleysols Gypsisols Histosols Kastanozems Leptosols Luvisols Phaeozems Planosols Podzols Regosols Solonchaks Solonetzs Umbrisols Vertisols Man made soils Rock outcrops Water bodies Lagoons Glaciers Urban areas miscellaneous units at the second level. Abbreviations are the ones proposed by the WRB (FAO, 1998). Tables 3 and 4 show the relative importance of dominant and subdominant soils in each BGRE at the first and second levels of the WRB (FAO, 1998), respectively. Table 5 highlights the strength of correlation between the various BGRE using pedotaxa at the first level. Fig. 2 shows the Soil Map of Europe overlain by the boundaries of the BGRE, while Fig. 3 shows the clustering of the BGRE using the WRB pedotaxa at the first level. Nitisols, Plinthosols, Lixisols and Durisols do not appear because they are typical of tropical environments Arctic biogeographical region In the Arctic region, relief varies from high mountains to low-lying plains (RCMC, 2000). Typical landscape features include rocky terrains and rock outcrops, frost debris, swamps, glaciers, and meadows (Schultz, 2002). Cryosols are dominant in the Arctic region, followed by Histosols, Podzols, and Albeluvisols (EC, 2010; FAO, 2001). Rocky terrains and rock outcrops cover considerable areas. Dominant pedotaxa at the second level are histic and turbic Cryosols, and gelic Histosols. Soil assemblages comprise 13 and 36 pedotaxa at the first and second WRB levels, respectively. Only one endemic soil minority appears in this region, corresponding to oxyaquic Cryosols Boreal biogeographical region The Boreal region is the largest biogeographical region of Europe, covering about 25% of its territory. Most of the region lies below 500 m above sea level. Large undulating plains and rolling hills resulting from the glacial and post-glacial erosion of weathered sedimentary rocks and igneous-metamorphic bedrocks are the dominant landscape features (EEA, 2002). At global scale, this biome has the largest extents of Podzols, Cambisols, Histosols, and Umbrisols (Schultz, 2002). However, in the European Boreal region, Albeluvisols are the dominant soils, followed by Podzols and Histosols, covering together 78% of the region (EC, 2004, 2010). Water bodies represent 3% of the area. Dominant pedotaxa at the second level are umbric Albeluvisols, followed by haplic, rustic and entic Podzols, histic Albeluvisols, and dystric and gelic Histosols. In total, 18 and 63 pedotaxa occur in this region at the two levels, respectively. The only endemic soil minority, located in Russia, corresponds to gleyic Cryosols Continental biogeographical region The Continental region is a land belt that crosses most of middle Europe from east to west. Together with the Boreal region, it is the largest biogeographical region of the continent, covering about 25% of its territory (EEA, 2002). Soil patterns show a gradation from northwest to southeast (EC, 2001). With decreasing rainfall, Podzols are progressively replaced by Luvisols and Cambisols (EC, 2001). Histosols and Gleysols are important in the northern lake area and in poorly drained valleys (EC, 2005). Chernozems formed on loess are widespread in the eastern part of the region. Cambisols dominate in the Continental region, followed by Phaeozems, Chernozems, Albeluvisols, Luvisols, and Fluvisols, covering together more than 75% of this territory. At the second level, albic Phaeozems are the most extensive soils. Umbric Albeluvisols, dystric and eutric Cambisols, chernic and luvic Chernozems are also representative pedotaxa in this region, each covering more than 10% of the territory. This is the region with the largest variety of pedotaxa at the second level (108), together with 25 pedotaxa at the first level. Two endemic soil minorities are present, corresponding to salic Histosols and yermic Cryosols Steppic biogeographical region The Steppic region stretches from Romania in the west, across the lower section of the floodplain of the Danube, along the north of

5 146 J.J. Ibáñez et al. / Geoderma 192 (2013) Table 2 Soil assemblages at the second level of the WRB (FAO, 1998) in areal percentages of each BGRE. Pedotaxa 2nd level Alpine Arctic Boreal Atlantic Mediterranean Continental Pannonian Black Sea Steppic Albeluvisols Endoeutric Gleyic Haplic Histic Siltic Umbric Acrisols Ferric Gleyic Haplic Plintic * Humic Alisols Plintic Andosols Dystric Humic Mollic Vitric Arenosols Albic Haplic Protic Anthrosols Arenic Terric Plaggic Chernozem Calcic Chernic Gleyic Glossic Haplic Luvic Calcisols Aridic Haplic Salic Cambisols Calcaric Haplic Chromic Dystric Eutric Gleyic Humic Mollic Vertic Cryosols Gleyic Haplic Histic Oxyaquic Turbic Umbric Yermic Fluvisols Calcaric Dystric Eutric Gleyic Haplic Histic Mollic Salic Thionic Umbric Gleysol Calcaric Calcic Dystric Eutric Haplic Histic Humic Mollic Sodic Thionic Gypsisols Aridic Histosols Dystric Eutric Fibric Gelic Cryic Sapric

6 J.J. Ibáñez et al. / Geoderma 192 (2013) Table 2 (continued) Pedotaxa 2nd level Alpine Arctic Boreal Atlantic Mediterranean Continental Pannonian Black Sea Steppic Salic Kastanozems Calcic Haplic Luvic Leptosols Calcaric Dystric Eutric Haplic Humic Lithic Mollic Rendizic Umbric Luvisols Albic Arenic Calcic Chromic Dystric Ferric Gleyic Haplic Vertic Phaeozem Albic Calcaric Gleyic Haplic Luvic Sodic Planosols Albic Dystric Eutric Haplic Luvic Mollic Podzols Carbic Entic Gleyic Haplic Leptic Placic Rustic Umbric Regosols Calcaric Dystric Eutric Gelic Haplic Solonchaks Gleyic Haplic Takyric Solonetzs Gleyic Haplic Mollic Umbrisols Arenic Gleyic Vertisols Chromic Gleyic Haplic Pellic Man made soils Rock outcrops Lagoons Water Bodies Glaciers Urban areas the Black Sea, to the foothills of the Caucasus. A large proportion of the region corresponds to the Caspian depression, with bottom areas lying as low as 30 m below sea level (Bridges, 1990). Typically, Chernozems are found in the north, along the border with the contiguous Continental region (EEA, 2002). Towards the south, with increasing aridity, Chernozems become progressively shallower and poorer in humus and give way to Kastanozems in the Black Sea area. Chernozems occupy about 50% of the Steppe region. Kastanozems, Fluvisols, Calcisols, Phaeozems, and Solonetzs are subdominant. At the second level, the calcic Chernozems dominate, followed by chernic Chernozems, haplic and luvic Kastanozems, endosalic Calcisols, and haplic Solonetzs. In total, 20 and 65 pedotaxa occur in this region at the two levels, respectively. Endemic soil minorities include mollic Planosols, haplic and salic Calcisols, and calcic Gleysols.

7 148 J.J. Ibáñez et al. / Geoderma 192 (2013) Table 3 Dominant and subdominant soil types at the first level of the WRB (FAO, 1998) in areal percentages of each BGRE. Pedotaxa 1st level (WRB) Dominant pedotaxa Subdominant pedotaxa Bioregion Pedotaxa Area % Pedotaxa Area % Alpine Cambisol 23.0 Leptosol 21.9 Arctic Cryosol 26.3 Histosol 9.2 Boreal Albeluvisol 36.5 Podzol 27.9 Atlantic Cambisol 24.6 Luvisol 15.8 Mediterranean Cambisol 36.8 Leptosol 19.2 Continental Cambisol 17.1 Phaeoem 15.9 Pannonian Phaeozem 24.1 Luvisol 13.7 Black Sea Chernozem 23.1 Luvisol 21.7 Steppic Chernozem 47.7 Kastanozem 15.1 Macaronesian Leptosol 25.3 Cambisol Atlantic biogeographical region The Atlantic region closely interacts with the bordering northeast Atlantic Ocean and the North Sea, extending from Portugal in the south to Norway in the north. Very acid soils such as Podzols are extensive in the north, in contact with the Boreal region; elsewhere Cambisols, Luvisols, and Fluvisols are the dominant soils (EC, 2005). Peat deposits are frequent in the most humid territories such as in Ireland and Scotland. Leptosols occur in the southernmost areas, mainly in hilly and mountainous landscapes (EC, 2005). Cambisols cover approximately 25% of the Atlantic region. Luvisols, Gleysols, Podzols, Leptosols, and Fluvisols are less extensive. Urban areas cover about 1.5% of the territory, and water bodies are also abundant. At the second level, haplic Luvisols are the dominant soils, followed by eutric and dystric Cambisols, haplic Podzols, dystric Histosols, and gleyic Luvisols. In total, 22 and 69 pedotaxa occur in the region at the two levels, respectively. Endemic soil minorities include plaggic Anthrosols, takyric Gleysols, haplic Fluvisols, and haplic Planosols; the latter two appearing only in the UK. Placic Podzols are idiosyncratic soils of Ireland and the UK but do not occur in the continental part of the Atlantic region Alpine biogeographical region The Alpine region includes some of the oldest as well as some of the most recent mountains of the world from the Mediterranean to western Siberia. Cambisols and Leptosols are the most representative soils. Podzols, Regosols, Phaeozems, and Albeluvisols also cover large extents. Rock outcrops and glaciers are idiosyncratic miscellaneous areas, similar to the arctic BGRE. At the second level, haplic Podzols dominate, together with subordinate dystric Cambisols, dystric Regosols, alpic Phaeozems, rendzic Leptosols, and eutric Cambisols. This is the region with the second largest variety of pedotaxa at the second Table 4 Dominant and subdominant soil types at the second level of the WRB (FAO, 1998) in areal percentages of each BGRE. Pedotaxa 2nd level (WRB) Dominant pedotaxa Subdominant pedotaxa Bioregion Pedotaxa Area % Pedotaxa Area % Alpine Haplic Podzol 13.1 Dystric Cambisol 11.9 Arctic Histic Cryosol 11.7 Turbic Cryosol 10.3 Boreal Umbric Albeluvisol 19.7 Haplic Podzol 14.6 Atlantic Haplic Luvisol 9.7 Dystric and Eutric 8.3 Cambisol Mediterranean Calcaric Cambisol 15.2 Eutric Cambisol 9.4 Continental Albic Phaeozem 9.5 Umbric Albeluvisol 8.2 Pannonian Calcaric Phaeozem 9.8 Gleyic Phaeozem 7.8 Black Sea Chromic Luvisol 19.6 Calcic Chernozem 12.2 Steppic Calcic Chernozem 23.6 Chernic Chernozem 20.9 level (105), together with 26 pedotaxa at the first level. The only endemic soil minority corresponds to humic Cambisols that occur in the Caucasian range Mediterranean biogeographical region The Mediterranean region has a varied and contrasted relief, with a mosaic of hilly-lands, mountains, plateaus, inland and coastal plains, together with several characteristic peninsular configurations and a large number of islands. At global level, Planosols and Calcisols are idiosyncratic soils of the Mediterranean biome. However, the same does not occur in the Mediterranean BGRE (Ibáñez et al., 1998). Cambisols dominate, followed by Leptosols, Luvisols, Regosols, and Fluvisols, that all together cover around 90% of this territory. At the second level, the most widespread unit corresponds to calcaric Cambisols, being also representative eutric and chromic Cambisols, calcaric Leptosols, and calcaric Regosols. In total, 25 and 74 pedotaxa occur in this region at the two levels, respectively. Eutric soils and calcareous parent materials and soils are most representative in this territory, related to the marine sediments that have deposited in the collision fringe between African and European plates. This region, especially the Iberian Peninsula, contains a large variety of endemic soil minorities, including plinthic, ferric and gleyic Acrisols, ferric Luvisols, aridic Gypsisols, aridic Calcisols, and takyric Solonchaks. Andosols occur in Sardinia, Sicily (Dazzi, 2007) and several Aegean Islands, but many of them are not recorded in the European Soil Database. The Mediterranean region is the only continental area that has one idiosyncratic pedotaxum at the first WRB level, i.e. Alisols Pannonian biogeographical region The Pannonian region corresponds to the central Danubian basin, with the Great Hungarian plain as core physiographic feature (Ostergren and Rice, 2004). Most of the region is covered by Chernozems on loess in the plains and Phaeozems in drier floodplain areas. Fluvisols have developed on recent alluvial deposits on riversides. The presence of shallow groundwater and its evaporation have caused the formation of Solonchaks and Solonetzs (EC, 2005). Luvisols and Cambisols are frequent in highlands, while Andosols and Cambisols are common in volcanic mountains. Steppe soils such as Phaeozems and Chernozems occupy about 35% of the Pannonian region, being also representative the Luvisols, Cambisols, Fluvisols, and Gleysols. At the second level, calcaric Phaeozems dominate, followed by calcic Chernozems, gleyic Phaeozems, haplic Luvisols, and haplic Phaeozems, with each one of these covering more than 10% of the territory. On the whole, 18 and 60 pedotaxa occur in this region at the two levels, respectively. Whether Phaeozems and Chernozems were the representative soils of the original deciduous forest landscape is a matter of debate. It is likely that the current steppe and grassland vegetation and associated soilscapes are the cultural product of long-lasting traditional land use Black Sea biogeographical region The Black Sea region consists of the coastal land that surrounds the southern half of the Black Sea and includes a variety of landscapes from lowlands to highlands. Chernozems and Luvisols are the dominant pedotaxa, together with subordinate Regosols, Fluvisols, Leptosols, and Vertisols. At the second level, chromic Luvisols dominate, being also representative calcic and haplic Chernozems, calcaric Fluvisols, and pellic Vertisols. Lagoons, marshes, and other water bodies cover more than 13% of this territory. In total, 19 and 36 pedotaxa occur in this region at the two levels, respectively. There are no pedotaxa or soil assemblages idiosyncratic of this biogeographical region.

8 J.J. Ibáñez et al. / Geoderma 192 (2013) Table 5 Correlation between the BGRE using the pedotaxa at the first level of the WRB (FAO, 1998). Alp Ar Bor Atl Med BS Con Ste Pan Mac Alpine Arctic Boreal Atlantic Mediterranean Black Sea Continental Steppic Pannonian Macaronesian Legend: Alp (Alpine), Ar (Arctic), Bor (Boreal), Atl (Atlantic), Med (Mediterranean), BS (Black Sea), Con (Continental), Ste (Steppic), Pan (Pannonian), Mac (Macaronesian). Correlations are significant at pb Macaronesian biogeographical region The Macaronesian region refers to a group of volcanic islands in the Atlantic Ocean, including the archipelagos of the Azores, Madeira, and the Canary Islands. Leptosols, Cambisols, and Calcisols are the most widespread pedotaxa, followed by Andosols and Solonchaks. At the first level, 20 pedotaxa appear in this region which constitutes an intraplate hotspot. There are no soil data available at the second WRB level for this region (Ibáñez and Effland, 2011). 4. Discussion 4.1. Soil geography At worldwide level, there are clear positive relationships between pedodiversity and the number of biomes and tectonic segments of each continent (Caniego et al., 2007). Similarly, the number of pedotaxa, or soil richness, is positively correlated and increases with the surface area of the continents (Ibáñez et al., 1998). The mountain biome has the highest pedorichness at global as well as at European level. The biomes closest to the poles have lower pedodiversity, and this trend occurs also on the European continent (Ibáñez et al., 1998). With exception of the Black Sea and Pannonian regions, most BGRE have idiosyncratic soil assemblages, although the correspondence between BGRE and their respective soil assemblages is somewhat fuzzy. Climate is the dominant soil forming factor at small-scale soil geography at both WRB levels but especially at the level of Major Soil Groups (Tables 1 and 2). In general, soil assemblages are more similar between contiguous BGRE than between disjoint ones, because the ecotones between neighboring regions are more than often gradual (Ibáñez et al., 1998). Other factors may also have played a role, such as for instance inaccuracies in BGRE delineation and/or the effect of Holocene climate changes on modifying the boundaries of the environmental units after the last glaciation (Ibáñez et al., 1998). From the dendrogram of Fig. 3, three main BGRE clusters can be distinguished on the basis of the pedotaxa at the first WRB level that constitutes their respective soil assemblages. One cluster links the cold soilscapes of the Arctic and Boreal regions, although their respective soil assemblages show significant differences. The second cluster shows the affinity between the Atlantic and the Mediterranean regions that have relatively similar soil assemblages. The Alpine region relates also to this cluster because of its varied soil assemblages and the abundance of Cambisols. All three regions have, in general, pedotaxa with weakly developed horizonation (Cambisols) and pedotaxa with Bt horizons under forest conditions (Luvisols). The third group includes the rest of the BGRE that are characterized by typical grassland soils (Chernozems, Kastanozems, and Phaeozems) mixed with forest soils (mainly Luvisols). The dendrogram highlights the relationship between the Continental and the Pannonian regions. The latter is in fact a patch within the matrix of the former, with an idiosyncratic paleogeographic evolution and land use history that determine its current climate and soil assemblages (EEA, 2002). Likewise, the soil assemblages of the Steppic and Black Sea regions are related because the latter can be considered a variant of the former and/or a frontier area with the Anatolian Asiatic region. Table 5 shows the matrix of correlation between BGRE using the pedotaxa at the first WRB level (FAO, 1998). From a pedological point of view, the most idiosyncratic is the Artic region that is not positively correlated with the other BGRE. The second one is the Boreal region whose soil assemblage is only weakly related to the continental one, mainly along its southern boundary. The third one corresponds to the Steppic region whose soil composition shows affinity only with the bordering Black Sea and Continental BGRE. This reiterates the similarity between regions with steppe environment (i.e. the Steppic, Pannonian, and Black Sea BGRE). The soilscapes of the Macaronesian archipelagos are mainly related with the soil assemblages of the Mediterranean and Alpine regions and, to a lesser extent, with those of the Atlantic region. This resemblance is because the larger isles (e.g. Canaries) have a mild Mediterranean climate and most of them are mountainous, while the Azores and Madeira archipelagos enjoy a very mild Atlantic climate. The remaining BGRE have soil assemblages related with those of their neighboring regions Soil minorities The scale of the European Soil Database (V2.0) (EC, 2004) is too small to carry out a fine analysis of the soil cover. However, at the date it is the only source of harmonized soil inventory information at continental level. Because of map generalization procedures or variable soil sampling densities in the contributing countries, the pedotaxa populations might be incomplete in some areas, especially concerning soil minorities and endemic soils. On the basis of the definitions provided in Section 2.4, the following soil minorities and endemic soils were identified: 1. Endemic biogeographical pedotaxa: there are 20 soil types of this class that are described together with the main soil assemblages of each BGRE. 2. Endemic geographical pedotaxa: they include the following pedotaxa: (a) Plaggic Anthrosols: Atlantic and Mediterranean BGRE (Iberian Peninsula); (b) Gleyic Chernozems: Continental and Atlantic BGRE (north of Central Europe); (c) Gelic Regosols: Alpine and Arctic BGRE (northern Scandinavian shoreline); (d) Yermic Cryosols: Boreal and Continental BGRE (east of Central Europe); (e) Luvic Planosols: Alpine and Steppic BGRE (northeast of the Black Sea); (f) Arenic Umbrisols: Atlantic and Mediterranean BGRE (shoreline in Portugal); (g) Mollic Fluvisols: Pannonian in contact with Continental and Alpine BGRE; (h) Haplic Cambisols: Atlantic and Continental BGRE (several adjacent patches); (i) Gleyic Vertisols: Mediterranean and Alpine BGRE (small areas in the Balkans).

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10 J.J. Ibáñez et al. / Geoderma 192 (2013) Alpine Atlantic Mediterranean Macaronesian Arctic Boreal Black Sea Steppic Continental Pannonian Fig. 3. Cluster analysis of the BGRE using pedotaxa at the first level of the WRB (FAO, 1998) (using complete linkage). 3. Disjoint soil minorities: they include the following pedotaxa: (a) Umbric Leptosols: mainly Steppic but also Alpine BGRE (Central Europe); (b) Mollic Andosols: Mediterranean and Continental BGRE (Italy and Central Massif of France); (c) Dystric Andosols: Mediterranean, Alpine, and Continental BGRE (Central Massif in France; continental Greece and Aegean islands; and Carpathian ranges); (d) Umbric Andosols: Mediterranean, Alpine, and Continental BGRE (Central Massif in France; continental Greece and Aegean islands; and Carpathian ranges). 4. Relatively dispersed or widespread soil minorities: they include the following pedotaxa: (a) Salic Fluvisols: Continental and Steppic BGRE (small patches along the southeastern border of the continent); (b) Gleyic Solonchaks: several BGRE (southern half of the continent); (c) Calcic Kastanozems: Mediterranean, Black Sea, and Steppic BGRE (southeast of Europe); (d) Albic Arenosols: Atlantic, Boreal, and Continental BGRE (shorelines of northern Europe); (e) Umbric Fluvisols: Boreal and Steppic BGRE (few areas in the north and southeast of the continent); (f) Lithic Leptosols: Arctic and Alpine BGRE (few areas on the northern shoreline of Russia and in the northern Caucasian range, with very cold climate); (g) Gleyic Umbrisols: Boreal and Continental BGRE (dispersed small patches); (h) Humic Acrisols: Alpine, Boreal, and Continental BGRE (dispersed small patches); (i) Thionic Fluvisols: several BGRE (dispersed small patches, mainly in shoreline localities); (j) Dystric Luvisols: Continental, Pannonian, and Alpine BGRE (Central Massif in France and Central Europe around the Pannonian region); (k) Haplic Regosols: several BGRE (dispersed small patches). Some BGRE are richer than others in soil minorities and endemic soils. This is because of their complex geologic history and structure, geomorphic evolution, and physiographic configuration that create a variety of local conditions and ecological niches where soils departing from the idiosyncratic soils form. The Mediterranean region, for instance, contains more endemic soil minorities than any other BGRE, with most of them in the Iberian Peninsula. The west side of this territory corresponds to an old craton with Paleozoic rocks partly covered by a Pliocene weathering mantle. In the southern parts that have not been exposed to glacial erosion during the Pleistocene, there are endemic soil minorities with old, nutrient-depleted soils such as plinthic, ferric and gleyic Acrisols, and ferric Luvisols. The eastern side of the Iberian Peninsula has two areas with the most arid climate of Western Europe and contains large extents of Miocene inland-sea evaporites. Three endemic soil minorities result from these conditions, including aridic Calcisols, takyric Solonchaks, and aridic Table 6 Pedodiversity of the BGRE at the first WRB level (FAO, 1998). BGRE S H E S/area 1 M Area Area % Alpine , Arctic , Boreal ,845, Atlantic , Mediterranean , Continental ,589, Pannonian , Steppic ,142, Black Sea Macaronesian , S=richness; H =Shannon Index (Shannon and Weaver, 1949); E=equitability; area = area of each biogeographical region in km 2. Gypsisols. Half of the endemic soil minorities of the Atlantic region, including haplic Fluvisols, haplic Planosols, and placic Podzols, only appear in the British Isles, reflecting the particular geographical history of this archipelago as compared to the Atlantic part of the continent. Furthermore, some endemic soil minorities occur exclusively in the southeastern part of the continent, in small adjacent areas of different BGRE, reflecting distinctive geographical histories Pedodiversity and pedorichness Tables 6 and 7 show the results of the pedodiversity analysis for each BGRE. Richness values (S), or number of pedotaxa, both for the first and second levels of the WRB (FAO, 1998) vary according to the size of the BGRE and the latitude. Thus, the BGRE with less pedotaxa are small ones and/or are located nearest to the North Pole (i.e. Arctic and Boreal BGRE). This pattern is similar to the fragmentation of the global pedosphere into climate zones or biomes (Ibáñez et al., 1998). The numbers of soil types (i.e. pedorichness) of the BGRE increase with their respective surface areas conforming to a power law, as it also occurs in all pedodiversity analyses, independent of the scales and areas under study (Ibáñez et al., 2009). Tables 6 and 7 show that pedorichness at the first and second WRB levels follows similar patterns for all BGRE. This trend is true whether pedorichness is analyzed using absolute values or in relation to the area of each BGRE (density estimated as S/ area), with only minor differences. Therefore, the richness in pedotaxa at the first WRB level is a suitable indicator of that of the second one. However, when the pedorichness per area of each BGRE is considered (density), the small regions have the highest values but without endemic soil minorities. It is a rule that biodiversity values of small land tracts in a given study area (e.g. small islands of an archipelago) are the most difficult to predict. This deviation from the theory is not yet well understood and is known in the ecological literature as the small-island effect (e.g. Burns et al., 2009). Ibáñez et al. (2005a,b) recognized the same pattern in pedodiversity analysis, as well as the lack of idiosyncratic and endemic soils in small island pedogeography, and proposed an explanation thereof in pedological terms (Ibáñez and Effland, 2011). The deviation from the theory could be a sampling artifact of power law distributions (e.g. Ibáñez et al., 2005a,b). This sampling bias seems related to the fact that richness area curves follow power laws: as the area increases, more objects (pedotaxa, species) can be found on it, but not in a linear way because these objects (classes, taxa) are not infinite in number and they are not everywhere. Furthermore, the exponent of the power law of the pedorichness area relationship is less than 1 irrespective of the scale, both in pedodiversity and biodiversity studies (Ibáñez et al., 2005a,b, 2009). Fig. 2. a) The Soil Map of Europe. The red lines indicate the boundaries of the Biogeographical Regions of Europe (see Fig. 1).

11 152 J.J. Ibáñez et al. / Geoderma 192 (2013) Table 7 Pedodiversity of the BGRE at the second WRB level (FAO, 1998). BGRE S H E S/area 1 M Area Area % Alpine , Arctic , Boreal ,845, Atlantic , Mediterranean , Continental ,589, Pannonian , Black Sea Steppic ,142, S=richness; H =Shannon Index (Shannon and Weaver, 1949); E=equitability; area=area of each biogeographical region in km 2. As a consequence of the former, small territories (e.g. Black Sea, Macaronesian, and Pannonian regions) have higher diversities when the density is taken into account. However, in absolute terms, the driving force of the area effect acts opposite to the small-island effect. In other words, when the area increases, the pedorichness increases more or less depending on the habitat heterogeneity of the territory studied (Ibáñez et al., 2005a,b). However, a phenomenological explanation is also feasible. The Pannonian region consists of plains and surrounding mountains. The latter have soil assemblages similar to those of the Continental BGRE, including steppe and forest soils. The Macaronesian region consists of archipelagos some of which have Atlantic climate and others have Mediterranean climate. In the latter, volcano slopes exposed to the trade winds are moist, while the opposite slopes are arid. These contrasting conditions repeat over small territories (see values in Tables 6 and 7). Finally, the Black Sea region is a heterogeneous region that includes a variety of climate conditions (i.e. Mediterranean, Continental, and Steppic) and soilscapes. In absolute terms, the Alpine region is the richest in habitat heterogeneity over short distances (e.g. soil and vegetation catenas, altitudinal climate belts). Environmental heterogeneity is compounded by the fact that the region is spatially fragmented and spread across the continent, with reliefs of different origin, age, and lithology. Therefore, the Alpine region is highly diverse in soils, coming just after the Continental and the Mediterranean regions. The same trend can be observed in mountainous and Mediterranean biomes at global level (Ibáñez et al., 1998; Minasny et al., 2010). In general, area and relief are correlated via power laws, and both of them are correlated with pedorichness and pedodiversity (Ibáñez and Effland, 2011; Ibáñez et al., 2005a,b). This could explain why the Continental region has high pedorichness and pedodiversity. Likewise, the high values of the Alpine and the mountainous Mediterranean regions seem to correspond to the relief effect. Pedodiversity as shown by the Shannon Index (H ) follows different patterns because of differences in equitability (E). In the small BGRE, equitability values are higher and thus also their respective pedodiversities. This means that the areas covered by the pedotaxa are more equitably distributed in smaller than in larger biogeographical regions where climate-controlled taxa are in general dominant. The only exception to this pattern is the Alpine region with idiosyncratic soils distributed according to climatic altitudinal belts. It is rather intuitive that in regions with only a few dominant pedotaxa, equitability (E) values are lower than in others, decreasing the relation between pedorichness and pedodiversity. 5. Conclusions The analysis of the soil assemblages and pedodiversity of the European continent shows that most BGRE are characterized by dominant soils, mainly controlled by the climatic conditions prevailing in each regional context. However, driving forces other than climate must be taken into account to explain the soil assemblages, as for instance geology and relief in the case of the Iberian Peninsula and the British Isles, or paleogeographic evolution and land use history in the case of the Pannonian region which seems to be a patch within the Continental region. Although the Black Sea area is not a soil region on its own, it is an interesting and very special hotspot from a biodiversity point of view. Soil assemblages of the northern cold regions are clearly different from those of the other regions. The Atlantic and Mediterranean regions and, to some extent, the Alpine region are mutually related. Finally, most continental soilscapes constitute a mix of typical steppe and forest soils. Endemic soil minorities have been identified in many BGRE, with varying patterns from region-specific to transcontinental and from adjacent to disjoint. Equitability is higher in the BGRE with less dominant idiosyncratic pedotaxa. In the more homogeneous northern regions, there may be an indirect relation between area, relief, and pedodiversity. Although soil assemblages do not match exactly the biogeographical regions, they could be used to detect past climate changes. However, the European Soil Database may be too coarse to fully characterize and evaluate the pedodiversity of the European continent. Soils are part of our natural heritage and should be preserved as natural as possible in selected critical areas (Ibáñez et al., 2008). The design and implementation of a Pan-European network of natural soil reserves would allow using pristine or only slightly disturbed pedotaxa as benchmark soils for future soil monitoring purposes (Ibáñez et al., 2008). References Amundson, R., Guo, Y., Gong, P., Soil diversity and land use in the United States. 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