or obliterated by disturbance. Podzols with little or no E horizon development are often classified as brown Podzolic soils, also called Umbrisols or Umbrepts. Geographic distribution Podzols cover about worldwide and are usually found under sclerophyllous woody vegetation. By extent Podzols are most common in temperate and boreal zones of the Northern Hemisphere but they can also be found in other settings including both temperate rainforests and tropical areas. In South America Podzols occur beneath Nothofagus betuloides forests in Tierra del Fuego. Podzolization Podzolization (or Podsolization) is complex soil formation process by which dissolved organic matter and ions of iron and aluminium, released through weathering of various minerals, form organo-mineral complexes (chelates) and are moved from the upper parts of the soil profile and deposit in the deeper parts of soil. Through this process, the eluvial horizon becomes bleached and of ash-grey colour. The complexes move with percolating water further down to illuviated horizons which are commonly coloured brown, red or black as they accumulate and consist of cemented sesquioxides and/or organic compounds. The podzolization is a typical soil formation process in Podzols. Preconditions Podzolization usually occurs under forest or heath vegetation and is common in cool and humid climates as these climates inhibit the activity of soil microbes in the topsoil. Overall, podzolization happens where the decomposition of organic matter is inhibited and as a result, acidic organic surface (mor) layers build up. Under these typically acidic conditions, nutrient deficiency further hampers the microbial degradation of organic complexing agents. Medium to coarse textured soils with base-poor parent material (usually rich in quartz) also promote podzolization, as they encourage percolating water flow. Key steps The soil-forming process of podzolization can be broken down into two main steps: Mobilization and translocation of organic matter, Fe and Al from the surface horizon, and Immobilization and stabilization of organic matter, Fe and Al into the subsoil. In the topsoil of acidic soils, organic matter (mostly from plant litter, the humus layer and root exudates) together with Al- and Fe-ions, form organo-mineral complexes. These soluble chelates then relocate with percolating water from the A (or E horizon) to the B horizon. As a result of this, the E horizon (or Ae horizon in the Canadian system of soil classification) is left bleached and ash-grey in colour, while the B horizon becomes enriched with relocated organo-mineral complexes. The colour of B horizon is consequently red,