• Duff:  Partially to fully decomposed organic material between the Litter-Lichen-Moss (LLM) stratum and mineral soil. Duff is described in two layers: an upper (Fermentation) layer and a lower (Humus) layer.
• Squirrel middens:  Mounds of litter, tree cones and other plant material accumulated by squirrels; currently only applicable to a few forested fuelbeds to boreal spruce-dominated forests in Alaska.
• Basal accumulations:  Accumulations of bark, downed woody debris, litter and duff surrounding tree trunks. 

Many FCCS fuelbeds may not have a ground fuels stratum or will be missing one or two categories. In these cases, some or all panels are grayed out and the "Not Present" button is checked.

Duff Category

Duff is partially to fully decomposed organic material and is generally located between litter and mineral soil. Duff is described in two layers: upper duff (fermentation layer; equivalent to the Oe organic soil horizon) and lower duff (humus layer; equivalent to the Oa organic soil horizon).