n. Upper duff is composed of recognizable leaves, needles, and other organic material in various states of decomposition and is and the equivalent of the fermentation layer (F- Layer) or Oe organic soil horizon in forest soil.
Upper duff is also called the Oe soil horizon and the fermentation layer (or F-layer). The classification of the duff layer into upper duff and lower duff has not yet been standardized and a number of criteria have been used to define the boundary between the two layers. Brown and others (1991) stratified the duff layer into shallow duff and lower duff, which includes deep pockets of rotten wood. Jandt and others (2005) stratified duff from boreal forest sites into upper and lower layers based on physical characteristics. They characterized upper duff as randomly oriented, compacted moss and organic material that is beginning to decompose.
The Fuel Characteristic Classification System (FCCS) defines upper duff as the fermentation layer, equivalent to the Oi organic soil horizon (Fire and Environmental Applications Team 2007).