Umbrisol, Umbrisol soil profile from Sweden, showing a humus-rich surface layer formed under forest cover and high rainfall.© ISRIC, www.isric.nlone of the 30 soil groups in the classification system of the Food and Agriculture Organization (FAO). Umbrisols are characterized by a surface layer that is rich in humus but not in calcium available to plants, owing to high rainfall and extensive leaching that lead to acidic conditions. They are found under forest cover in high-rainfall regions of western Europe, the Pacific Coast of North America north of California, the southwestern coast of South America, and the Himalayas. Umbrisols occupy about 0.8 percent of the total continental land area on Earth and are related to soils of the Inceptisol order of the U.S. Soil Taxonomy that form under coniferous forest vegetation. They are the forestland counterpart of Chernozems, Kastanozems, and Phaeozems in exhibiting a humus-rich surface layer.