Charcoal hearth soils should be better accounted for by the WRB and the Soil Taxonomy

Abstract The legacy of charcoal making, an old and widespread forest exploitation activity, is a plethora of charcoal hearth (CH) soils that occur all around the world with peculiar features, the main of which is a top, thick, black, charcoal-rich horizon. Being substantially due to human activity, these soils are anthropogenic or “human-altered and human-transported” soils. However, the two most widely used classification systems—the World Reference Base for Soil Resources and the U.S. Soil Taxonomy—which in their last versions give credit to major human-induced soil features, fail to satisfactorily account for their origin and most significant features. In this paper we discuss the classification of CH soils to underline what we perceive as gaps preventing proper reporting of these particular soils. This is in the hope that it will support the working groups responsible for updating the aforementioned classification systems. The WRB's Reference Soil Group of Technosols is a convincing framework for CH soils in consideration of their history and the occurrence of artefacts (charcoal). However, the very high required amount of artefacts prevents such an attribution, making the use of the supplementary qualifier Carbonic under other Reference Soil Groups the most plausible reference to the crucial role of humans on CH soils' genesis and shaping. The U.S. Soil Taxonomy in its latest version includes the Human-Altered and Human-Transported Soils (HAHTs), which are considered extragrades, since they do not represent an intergrade to any other taxon. HAHTs suit the CH soils as well, although only at the level of Subgroups (as Anthropic and Anthroportic intergrades) or, perhaps more comfortably, at the lower categorical detail, i.e., as Families (Pyrocarbonic). In our belief it is desirable that the future versions of the two aforementioned classification systems will adequately frame the CH soils, in consideration of both their widespread occurrence and distinctive features: the WRB allocating them irrefutably among the Technosols and the ST finally including them in a new Order of anthropogenic soils.