Article: article from journal or magazin.
Typologie des sols sur gypse et végétation associée en Suisse
Bulletin de la Société vaudoise des Sciences naturelles
Soils on gypsum are well known in dry climates, but were very little described in temperate climate, and never in Switzerland. This study aims to describe soils affected by gypsum in temperate climate and to understand their pedogenesis using standard laboratory analyzes performed on ten Swiss soils located on gypsum outcrops. In parallel, phytosociological relevés described the vegetation encountered in gypsiferous grounds. Gypsification process (secondary gypsum enrichment by precipitation) was observed in all soils. It was particularly important in regions where potential evapotranspiration exceed strongly precipitations in summer (central Valais, Chablais under influence of warm wind). Gypsum contents were regularly measured above 20% in deep horizons, and exceeded locally 70%, building a white, indurate horizon. However, the absence of such a gypsic horizon in the top soil hindered the use of gypsosol (according to the Référentiel pédologique, BAIZE & GIRARD 2009), the typical name of soils affected by gypsum, but restricted to dry regions. As all soils had a high content of magnesium carbonates, they were logically classified in the group of DOLOMITOSOLS. However, according to the World Reference Base for Soil Resources (IUSS 2014), five soils can be classified among the Gypsisols, criteria being here less restricting. These soils are characterized by a coarse texture and a particulate brittle structure making a filtering substrate. They allow water to flow easily taking nutrients. They are not retained by clay, which does generally not exceed 1% of the fine material. The saturation of calcium blocks the breakdown of organic matter. Moreover, these soils are often rejuvenated by erosion caused by the rough relief due to gypsum (landslides, sinkholes, cliffs and slopes). Hence, the vegetation is mainly characterized by calcareous and drought tolerant species, with mostly xerothermophilic beech (Cephalanthero-Fagenion) and pine forests (Erico-Pinion sylvestris) in lowlands, or subalpine heathlands (Ericion) and dry calcareous grasslands (Caricion firmae) in higher elevations.
pédologie, sol, Suisse, Alpes, gypse, végétation
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