A proposal for including humus forms in the World Reference Base for Soil Resources (WRB-FAO) Augusto Zanella 1 , Michael Englisch 2 Jean-François Ponge 3 , Bernard Jabiol 4 , Giacomo Sartori 5 , Ciro Gardi 6 ¹University of Padua, Department of Land, Environment, Agriculture and Forestry, Viale dell’Università 16, 35020 Legnaro, Italy; ² Bundesamt für Wald, Unit Site and Vegetation, Department of Fo- rest Ecology and Soil, Federal Research and Training Centre for Forests, Seckendorff-Gudent-Weg 8, 1131 Vienna, Austria; 3 Museum National Histoire Naturelle, CNRS UMR 7179, 4 avenue du Petit Château, 91800 Brunoy, France; 4 AgroParisTech, ENGREF-LERFOB, 14 rue Girardet, 54042 Nancy, France; 5 Museo Tridentino di Scienze Naturali, Trento, Italy; 6 European Commission, Institute for Environment & Sustainability - DG JRC, Ispra, Italy The last delivery of the World Reference Base for Soil Resources (IUSS Working Group WRB, 2006) updated previous texts adopted by the ISSS Council, and was proposed at the 18th World Congress of Soil Science as the official reference for soil nomenclature. It was considered by the entire soil community as the better framework “through which existing soil classification systems could be correlated and harmonized”. As in previous drafts, the humus form, i.e. the part of the topsoil which is strongly influenced by biological activities and organic matter (litter included), was only partially considered, taking into account organic layers only when their thickness was very high, and ignoring many fundamental evidences necessary for a sufficiently precise characterization of forest soils, as well as all soils not periodically ploughed. A modern, biologically meaningful classification of humus forms has been proposed at the European level by Zanella et al. (2011: a. A European morpho-functional classification of humus forms. Geoderma 164, 138-145; b. European Humus Forms Reference Base [http://hal.archives-ouvertes.fr/docs/00/56/17/95/PDF/Humus_Forms_ERB_31_01_2011.pdf]), encompassing a wide variety of humus forms, both in terrestrial and semi-terrestrial environments. This morpho-functional classification, which has been recently updated thanks to users’ feedbacks, is the basis of our proposal to include humus form characterization in the WRB, for the sake of completing and improving this soil classification system (Humus group life: Figs. 1 to 6) Following WRB specifications, two tiers of categorical detail have been performed: 31 Reference Humus Form Groups or RHFGs (tier 1), and the combination of RHFGs with prefixes and suffixes, detailing the properties of RHFGs by adding a set of uniquely defined qualifiers (tier 2). The architecture proposed for the RHFGs is based on the same principles as WRB: “[RHFGs] are allocated to higher-level groups on the basis of diagnostic characters, i.e. factors or processes that most clearly influence the biological formation of [humus forms]”. The 10 historical main groups of humus forms, elaborated by Zanella et al. (2011a, b) for classifying terrestrial humus forms (Mull, Moder, Mor, Amphi, Tangel) and semi-terrestrial humus forms (Mull, Amphi, Moder, Anmoor, Mor) and their second-level units (terrestrial: dys, eu, hemi, humi, lepto, meso, oligo, pachi; semiterrestrial: fibri, humi, limi, mesi, sapri) were combined to create a first-level classification of 31 RHFGs. Specific prefix and suffix qualifiers are then associated to RHFGs, allowing a wide variety of variants (second-level classification) to be defined according to biological (vegetation) and environmental (geology, climate) context. Fig 7: First general key of classification 2005 Fig 8: Last proposal; Fig 9: prefix and suffix qualifiers General Assembly of the European Geosciences Union, Soil System Sciences Division Austria Center Vienna (ACV): 22 -27 April 2012 Fig. 1. What’s a humus form ? 2003 Trento 2004 Vienna 2005 San Vito 2007 Cagliari HUMUS Group Three not well defined Commissions (classification, vocabulary, diffusion) Eurosoil 2004 Stato dell’arte origin of the Humus Group First common key (AMPHI) and paper Mediterranean ecosystems (FAO vocabulary) HUMUS GROUP structure and functioning: - No pyramidal structure - No classic organisation, no chief or president, no... - When matter is ready for discussion, every member should organisea meeting with the whole HG, or with a group of interested people - If results, then diffusion: 1. A European morpho-functional classification of humus forms. (GEODERMA, 2011) 2. European Humus Forms Reference Base(2011).. http://hal.archives- ouvertes.fr/docs/00/56/17/95/PDF/Humus_Forms_ERB_31_01_2011.pdf 3. Humus Form ERB. A European Reference Base for humus forms: proposal for a morpho- functional classification (2010).. http://hal.archives- ouvertes.fr/docs/00/54/14/96/PDF/Humus_Forms_ERB.pdf 4. Terrestrial Humus Forms: Ecological Relevance and Classification. European. (Atlas of Soil Biodiversity 2010). . 5. Towards a European humus forms reference base, (Studi trentinidi Scienzenaturali, 2009) 6. Towards a European classification of forest humus forms. Eurosoil - Freiburg. September 4-12. Symposium 09 - Forest soil Monday 6th: 9.30-9.50 (2004). http;//www.bobenkunde.uni- freiburg.de/eurosoil. Poster for the Congress Eurosoil 2008 Paris Trento 18° World Congress of Soil Science 2006 Freibourg Philadelphia AMPHI HISTO TANGEL 2006 Vienna Workshop: Leptoforms Rhizo, Ligno, Hydroforms 2008 2009-2011 - European Geosciences Union General Assembly 2012 - Bari (Italy): Eurosoil 2012 Diffusion 3 papers Fig. 2. European Humus Group‘s adventure Ils sont fous ces Romains Earthworms like that San Vito, 2005 Fig. 3. Not only humus box sample rubber ring spring (1,5 Kg) 2 Kg 1) sample in the box (Ø 2 - 3,5 cm) 2) let fall the box 5 times 1 cm3 1 jump = 100g/1,5 m (sample + box) system Fig. 4. Tests on A horizon structure 1 cm Diplopods Epigeic earthworms Encytraeids Insect larves Acarians Chilopods Isopods Spiders 1 1 2 2 2 3 3 3 4 4 4 4 5 5 6 6 6 7 7 7 8 8 8 Fig. 5. Humus forms and pedofauna Fig. 6. Key of soil biostructures Prefix qualifiers: haplic, lithic, peyric, psammic, rhizic, lignic, bryoic…. stagnic, epihistic, …..haplic DYSTANGEL EUTANGEL PACHYAMPHI EUMESOAMPHI EUMACROAMPHI LEPTOAMPHI OLIGOMULL EUMULL MESOMULL DYSMULL HEMIMODER EUMODER DYSMODER HEMIMOR HUMIMOR EUMOR EUANMOOR SAPRIANMOOR LIMIANMOOR LIMIMULL SAPRIMULL HUMIAMPHI MESIAMPHI FIBRIAMPHI SAPRIMODER HUMIMODER MESIMODRE FIBRIMODER MESIMOR FIBRIMOR (Suffix qualifiers): fluvic, novic, sodic, …. terric, albic, spolic, garbic…. Ex.: ENTI + PARA = PARAHUMUS 14 16 + = 31 HUMUS REFERENCES EUMODER (garbic) hyperrhizic Humus forms in which predominance of parent or plant materials arrests or masks incipient animal activity in terrestrial or semi-terrestrial ecosystems: PARAHUMUS 1+ Table 1. Prefix and suffix qualifiers used for the definition of humus forms. Qualifiers already used for the definition of soils (IUSS Working Group WRB, 2006) are indicated. Vocabulary refers to the present article or (*) to IUSS Working Group WRB (2006). PREFIX SUFFIX WRB 2006 DEFINITION, new or adapted for humus forms hyperlignic no having an OW horizon of more than 75% of the thickness of combined diagnostic horizons (Parahumus only) hyperrhizic no having an OR horizon of more than 75% of the thickness of combined diagnostic horizons (Parahumus only) hyperbryoic no having an OM horizon of more than 75% of the thickness of combined diagnostic horizons (Parahumus only) lignic yes (modified) having an OW horizon between 25 and 75% of the thickness of combined diagnostic horizons or having more than 25% of wood remains in the total volume rhizic no having an OR horizon between 25 and 75% of the thickness of combined diagnostic horizons or having more than 25% of dead or living roots in the total volume bryoic no having an OM horizon between 25 and 75% of the thickness of combined diagnostic horizons or having more than 25% of dead or senescent moss parts in the total volume folic yes whose OH horizon is ≥ 10 cm ombric yes having a histic* horizon saturated predominantly with rainwater stagnic yes having reducing conditions and OLg, OFg, OHg and/or Ag horizon with stagnic* colour patterns gleyic yes lying directly on a horizon with gleyic* colour patterns floatic yes having organic material floating on water epihistic no havingboth [(OL, OF, OH)g and/or Ag] and histic (H or Aa) horizons fluvic yes whose A horizon or first mineral horizon comes with evidence from fluvic* material novic yes having above the O horizon, a layer with recent sediments (new material < 1y.), 3 mm or more and less than 2 cm thick sodic yes having 15 % or more exchangeable Na plus Mg on the exchange complex in the A horizon alcalic yes having a pH (1:1 in water) of 8.5 in the A horizon calcaric yes whose A horizon is calcaric* material hypereutric yes having a base saturation (by 1 M NH4OAc) of 80 % or more in the A horizon eutric yes having a base saturation (by 1 M NH4OAc) of 50 % or more in the A horizon dystric yes having a base saturation (by 1 M NH4OAc) of less than 50 % in the A horizon hyperdystric yes having a base saturation (by 1 M NH4OAc) of less than 20 % in the A horizon clayic yes having a texture of clay in the A horizon arenic yes having a loamy fine sand or coarser texture in the A horizon hyperarenic no having a loamy fine sand or coarser texture within 2 cm of the soil surface without an A horizon under OLn (Parahumus only) lithic yes having continuous rock directly under the A horizon and within 10 cm of the soil surface hyperlithic no having continuous rock under OLn and within 2 cm of the soil surface (Parahumus only) skeletic yes having 40 % by volume or more of gravel or other coarse fragments in the A horizon and within 10 cm of the soil surface hyperskeletic yes containing less than 20 % by volume of fine earth within 2 cm of the soil surface hyperhumic yes having an organic carbon content of 5 % or more in the fine earth fraction to a depth of 20 cm or more rendzic yes whose A horizon is a mollic* horizon that contains 40 % or more calcium carbonate equivalent andic yes whose A horizon has andic* properties salic yes (prefix) whose A horizon is a salic* horizon albic yes with O horizons lying directly on an albic* horizon hortic yes whose A horizon is an hortic* horizon terric yes whose A horizon is a terric* horizon technic yes having 10 % or more artefacts in the A horizon urbic yes having 25 % or more artefacts, containing 35 % or more of rubble and refuse of human settlements, in the A horizon hyperurbic no having 75 % or more artefacts, containing 35 % or more of rubble and refuse of human settlements, in the A horizon spolic yes having 25 % or more artefacts, containing 35 % or more industrial waste, in the A horizon hyperspolic no having 75 % or more artefacts, containing 35 % or more industrial waste, in the A horizon garbic yes having 25 % or more artefacts, containing 35 % or more organic waste materials, in the A horizon hypergarbic no having 75 % or more artefacts, containing 35 % or more organic waste materials, in the A horizon erodic no having only remnants of diagnostic horizons, due to mechanical perturbation (erosion, waterlogging, actionof New starting point, 2005 Some examples Loranger (2001) and Loranger et al. (2003) described a humus form, called amphimull according to classification by Brêthes et al. (1995), in Carib- bean semi-evergreen secondary forests on pure hard calcareous substrate (tropical rendzina). This humus form was characterized by the presence of O horizons (OL 4 cm, OF 2 cm, OH 1.5 cm) overlying a biomacrostructured A horizon. According to our proposal it can be called EUMACROAMPHI, with the prefix haplic indicating that neither typically associated nor intergrade qualifiers apply, and the suffix rendzic indicating the pedogenetic con- text, hence haplic EUMACROAMPHI (rendzic). In a nearby forest plantation on deep vertisol a humus form with contrasting characters was called Eu- mull according to abovementioned literature. It was characterized by a thin (1 cm) OLn horizon overlying directly a deep biomacrostructured A horizon. According to our proposal this is a EUMULL (name unchanged) with the suffix eutric acknowledging for the base-saturated A horizon (IUSS Working Group WRB, 2006), hence haplic EUMULL (eutric). In a quite climatic (temperate) and geographic context (western Europe), Gillet and Ponge (2002) described a humus form, which they called mor, in a poplar plantation strongly polluted by heavy metals (Zn up to 40,000 mg.kg-1) where poplar failed and was replaced by thrift (Armeria maritima) vegetation. Plant remains accumulate in a context from which faunal and bacterial activities were excluded, resulting in thick O horizons (OL, 1 cm, OFnoz, 9 cm) lying directly on industrial waste products. Such a humus form can be called haplic EUMOR (spolic). Bullinger-Weber et al. (2007) described several types of humus forms in alluvial soils of the Swiss Alps, with strong changes in thickness and natu- re of diagnostic horizons according to riverbank successional status. The youngest profile (under willow) was described as a Eumull, according the abo- vementioned French classification. It exhibited characteristic features on initial soils in an otherwise calcareous context. It was characterized by the scar- ce presence of a very thin (when present) OLv horizon, overlying a thin (1 cm) weakly differentiated organo-mineral horizon without any traces of ani- mal activity visible to the naked eye and with a very poor content in organic matter, overlying in turn on sandy alluvial deposits. Given the impossibility to discern trends in the formation of diagnostic horizons (although faunal investigations on earthworms and enchytraeids testimony for incipient mull formation), such a humus form, without any structured O and A horizons, could be called PARAHUMUS, with hyperskeletic, hyperarenic as prefixes and fluvic and calcaric as suffixes, hence hyperskeletic hyperarenic PARAHUMUS (fluvic, calcaric). Hiller et al. (2005) described soils and humus forms in Swiss alpine tundra ecosystems, following for humus forms the British Colombian classifi- cation by Green et al. (1993). Outside snow beds, at alpine elevation (2800 m) they found a humus form they called Rhizic Mullmoder. It was characte- rized by the following sequence from surface to depth according to the here presented nomenclature of diagnostic horizons: an OLv horizon (5-6 cm), then an OFzo horizon with abundant roots (3-5 cm), then when present an OH horizon (0-3 cm) overlying with a wavy transition a single-grain A hori- zon. According to the present classification, such a humus form could be named HEMIMODER (because of the discontinuous OH horizon and the gra- dual transition from O horizons to a single-grain A horizon), with rhizic as suffix, hence haplic HEMIMODER (rhizic). Fons et al. (1998) described a new humus form, called ‘Lamimoder’, which was observed to occur in trembling aspen boreal forests and more ge- nerally in circumboreal broadleaf forests. It was characterized by a thick OF horizon in which nonzoogenic (OFnoz) horizons, with a dense root mat of aspen, were thicker than zoogenic (OFzo) horizons, overlying a continuous OH horizon. Unfortunately, no details were given of the transition of O to A (or E) horizons. According to our proposal, and supposing that the transition was abrupt (< 3 mm), this humus form could be called haplic HUMIMOR (rhizic). Fig. 7. First draft of a general (terrestrial and semi-terrestrial) humus forms classification Fig. 8. Last proposal of a WRB for terrestrial and semi-terrestrial humus forms Fig. 9. Proposal of WRB qualifiers for humus forms Mostly from Anecic and Endogeic (meso, endo-anecic, oligohumic) earthworms organomineral, homogeous pulp with mineral grains, cylindrical, often “boweled” MACRO Anecic and Endogeic earthworms Ø >= 4 mm Ø >1-3 mm From Diplopods and Myriapods: Asymmetrical pills with prysmatic tip, holorganic, heterogenous, composed of recognizable fragments of vegetables in cluster. From insects (almost larval stade of coleopters and dipters): spherical grains lumped together in 2 or 3, holorganic, homogeneous, composed of undeterminable organic fragments Ø 4 mm MICRO Enchytreids, Epigeic earthworms and Microarthropods From Collembola: holorganic and hemiorganic, not in cluster, cylindrical, lengthened, curved, irregular bound Ø =< 1 mm From Enchytreids, Epigeic earthworms: olorganic and hemiorganic, often in cluster, ovoid, regular bound Ø 1 mm Ø << 1 mm From Acarian: holorganic, spherical, very regular bound Mostly from Epigeic and Endogeic (polyhumic, mesohumic, endo-anecic) earthworms Holorganic and hemorganic, finely homogeneous pulp, spherical grain or short cylinder with conic tip Ø >1- 4 mm MESO Endogeic and Epigeic earthworms, Arthropods and Enchytreids 2 0.5 3 5