Folisol (FO)
Soils of the Folisol great group are composed of upland organic (folic) materials, generally of forest origin, that are either 40 cm or more in thickness, or are at least 10 cm thick if overlying bedrock or fragmental material. Deep Folisols (greater than 40 cm of folic material) occur frequently in cool, moist, and humid forest ecosystems, particularly on the West Coast of Canada. They also develop in northern regions where soil temperatures are low, but the soil is without permafrost. Shallow Folisols are found throughout Canada and commonly occur on upper slope shedding positions over bedrock and on, or incorporated in, fragmental or skeletal material.
Folic materials are formed under ecosystems different from those of peat materials. Folic materials are the product of upland ecosystem development, whereas peat materials are the product of wetland development.
Folisols are well to imperfectly drained, although they may become saturated after rainfall or snowmelt. They contain organic C at a level of >17% (about 30% or more Organic matter) by weight in diagnostic horizons. Folic materials qualify as Folisols if they meet the following criteria:
- Folic material is 40 cm or more in depth; or
- Folic material is 10 cm or more in depth if directly overlying a lithic contact.or fragmental material, or if occupying voids in fragmental or skeletal material; or
- Folic material is more than twice the thickness of a mineral soil layer if the mineral layer is less than 20 cm thick.
Folic materials containing permafrost at depths of 1 m or less are classified as Cryosolic soils.
The Folisol great group is divided into four subgroups, based on the degree of decomposition of the folic material (as distinguished by the diagnostic F and H soil horizons) or on the type of organic materials in the control section, or on both. Layers or pockets of decaying wood may be designated as an F or an H
Common horizon sequence: L, F, H, O, R, (M1) Soils of this subgroup are composed dominantly of the moderately decomposed F horizon in the control section and may have subdominant H and O horizons, each less than 10 cm thick. They commonly have a lithic contact or fragmental layers but meet the requirements of the Folisol great group. The F horizon consists of partly decomposed folic material generally derived from mosses, leaves, twigs, reproductive structures, and woody materials containing numerous live and dead roots. Common horizon sequence: L, F, H, O, R, (M1) Soils of this subgroup are composed dominantly of the well-decomposed H horizon in the control section and may have subdominant F and O horizons each less than 10 cm thick. A lithic contact, fragmental, or mineral layers may be common in the control section, but the soils meet the requirements for the Folisol great group. Humic Folisols occur most frequently in cool, moist, humid forest ecosystems. Although they occur in many landscape positions, they commonly develop on lower slopes and in valley bottoms. Rooting channels and other voids are common in these soils. Common horizon sequence: L, F, H, R, (M1) Soils of this subgroup are dominated by F or H horizons, which are composed primarily of moderately to well-decomposed woody materials. These materials occupy more than 30% of the surface area of the F and H horizons. The decaying wood that makes up the F and H horizons generally consists of trees that have been blown down. The destruction of trees is either a continuing process in unevenly aged forests or occurs at periodic intervals as a result of major storms, which create evenly aged forest stands. Lignic Folisols also occur in a second-growth forest as a result of logging. Common horizon sequence: L, F, H, O, R, (M1) Soils of this subgroup are dominated by F or H horizons and are directly underlain by a significant (greater than 10 cm) O horizon. Generally, saturation or high water tables (resulting from drainage impediment caused by mineral horizon cementation or localized bedrock configuration) initially encouraged the production of peat. Peat development subsequently became deep enough to produce surface conditions suitable for forest encroachment and Folisol development.Hemic Folisol (HE.FO)
Hemic Folisols usually occur on upper slope shedding positions and commonly consist of shallow folic material over bedrock or fragmental material, or the folic materials may occupy voids in fragmental material. There may be a thin layer of mineral soil separating the folic horizon from bedrock or from the fragmental material.Humic Folisol (HU.FO)
Lignic Folisol (LI.FO)
Histic Folisol (HI.FO)
Note: Diagnostic horizons are underlined.