FCCS fuelbeds are organized by stratum: general, canopy, shrub, herbaceous, wood, litter-lichen-moss, and ground fuel. An FCCS fuelbed is organized in a nested fashion according to the following structure.
| Stratum | Substratum | Layer | Definition |
|---|---|---|---|
| General | Descriptive data including fuelbed number, name, and description and ecological classifications | ||
| Canopy | |||
| Canopy | Trees | ||
| Canopy | Trees | Overstory | Dominant trees |
| Canopy | Trees | Midstory | Codominant or intermediate trees |
| Canopy | Trees | Understory | Understory trees, including seedlings and saplings |
| Canopy | Snags | Class 1 snags with foliage | Recently dead trees (in the overstory, midstory, or understory) that still have foliage |
| Canopy | Snags | Class 1 snags without foliage | Aka Class 1 other. |
| Canopy | Snags | Class 2 | Older dead trees. Coarse branches and bark are present. Wood is partially decayed. |
| Canopy | Snags | Class 3 | Older dead trees. Branches and bark not present. |
| Canopy | Ladder fuels | Vegetation (vines, shrubs, or saplings) creating vertical continuity between the lower vegetation strata and canopy layers | |
| Shrub | Shrubs are low woody plants, generally with multiple stems. There is no clear distinction between tall shrubs and short broadleaf deciduous or evergreen trees, and FCCS allows you to define them as either. | ||
| Shrub | Primary | The main layer of shrubs. Primary and secondary layer shrubs can be delineated by height, shrub species groupings, or any other classification you choose. | |
| Shrub | Secondary | The secondary shrub layer is an optional layer with a different species composition, height, biomass, or other distinguishing factor from the primary shrub layer. | |
| Herb | Nonwoody plants including grasses, sedges, forbs, and other herbaceous fuels. | ||
| Herb | Primary | The main layer of vegetation within the herb stratum. Users can determine the primary layer based on a number of selection criteria including species, height, mass, etc. | |
| Herb | Secondary | The secondary herb layer is an optional herb layer with a different species composition or height than the primary herb layer. | |
| Downed wood | All downed and dead woody material in a fuelbed | ||
| Downed wood | Sound wood | Downed and dead sound wood (3 fine and 3 coarse wood size classes) | |
| Downed wood | Rotten wood | Downed and dead rotten wood (3 coarse wood size classes). Rotten wood is defined as partially decomposed wood debris with obvious signs of decay, such that the material falls apart when kicked. | |
| Downed wood | Stumps | Remaining sawn or broken stems up to 1.4 m | |
| Downed wood | Stumps | Sound stumps | Bark intact; hard when kicked |
| Downed wood | Stumps | Rotten stumps | Bark may or may not be intact; represents decay classes 3, 4, and 5; feels soft or punky when kicked |
| Downed wood | Stumps | Lightered stumps | Rotten with resin-soaked heartwood; particularly common in Southeastern pine stands |
| Downed wood | Piles | Naturally occurring or human-made piles or accumulated downed wood | |
| Litter-Lichen-Moss | Litter, ground lichen, and moss (aka LLM) | ||
| Litter-Lichen-Moss | Litter | The top layer of the forest floor (also called the O1 or Oi organic soil horizon) and is composed of loose debris of dead sticks, branches, twigs, and recently fallen leaves or needles; little altered in structure by decomposition. | |
| Litter-Lichen-Moss | Lichen | Composite organisms made up of a fungus growing symbiotically with an alga or a cyanobacterium characteristically forming a crustlike or branching growth on rocks or tree trunks. Lichen grows on forest, shrubland, and grassland floors. Arboreal lichen are included as a type of ladder fuels in the canopy stratum. | |
| Litter-Lichen-Moss | Moss | Any of various green, usually small, nonvascular plants of the division Bryophyta growing on forest, shrub, and grassland floors, particularly in moist habitats. | |
| Ground fuels | Duff | Organic soil between the LLM stratum and mineral soil | |
| Ground fuels | Duff | Upper duff | The Oe soil horizon or fermentation layer. Partially decomposed organic matter in which tree needles, leaves, and other material are identifiable. |
| Ground fuels | Duff | Lower duff | The Oa soil horizon also called the humic layer. The lower duff layer, where it exists, contains mostly decomposed organic matter and is much denser than the upper duff layer. |
| Ground fuels | Baal accumulations | Accumulations of bark, downed wood, and forest floor surrounding tree trunks | |
| Ground fuels | Squirrel middens | Mounds of litter, tree cones, and other plant material accumulated by squirrels; these are generally limited to boreal-spruce-dominated forest fuelbeds in Alaska. |