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Canopy Fuel Characteristics

Canopy Cover, % or Class

The Forest Canopy Cover (CC) describes the percent cover or cover class of the tree canopy in a stand. Specifically, canopy cover describes the vertical projection of the tree canopy onto an imaginary horizontal surface representing the ground’s surface.  Estimate of Canopy Cover is used in adjustment of 20ft winds to mid-flame, in fuel moisture conditioning, and in spotting distance models. 

The scale here illustrates the look of representative canopy cover percentages and ranges within each cover class.

Canopy Cover classification.  This graphic depicts from above views of canopy cover and its effect on wind sheltering/reduction.

For surface fuels sheltered by a forest canopy on flat terrain (Scott 2007)

Canopy Cover Wind Sheltering
CC ≤ 5% Unsheltered
5% < CC ≤ 10% Partially Sheltered
10% < CC ≤ 15% Partially Sheltered
15% < CC ≤ 30% Fully Sheltered, Open
30% < CC ≤ 50% Fully Sheltered, Open
CC > 50% Fully Sheltered, Closed

Stand (Canopy) Height, ft or m

The Stand, or Canopy, Height (SH) describes the average height of the top of the vegetated canopy. Canopy Height estimates are used in adjustment of 20ft winds to mid-flame and in spotting distance models.

Canopy Base Height, ft or m

The Forest Canopy Base Height (CBH) describes the average height from the ground to a forest stand's canopy bottom. Specifically, it is the lowest height in a stand at which there is a sufficient amount of forest canopy fuel to propagate fire vertically into the canopy. Using this definition, ladder fuels such as lichen, dead branches, and small trees are incorporated. Estimate of Canopy Base Height is used in the Crown Fire Initiation model.

Describing a Forest Canopy. This graphic highlights the way to think about the primary descriptors for crown fire prediction. Crown Bulk Density describes the crown fuel load and distribution. Stand Height describes height of canopy tops. Crown Base height represents the difficulty for surfaces fires to ignite the canopy. And Foliar Moisture content suggest how readily the canopy will burn.

Canopy Bulk Density, kg/m3 or lb/ft3

The Forest Canopy Bulk Density (CBD) describes the density of available canopy fuel in a stand. It is defined as the mass of available canopy fuel per canopy volume unit.  Typical units are either kg/m3 (LANDFIRE default) or lb/ft3 (BehavePlus default).  Canopy Bulk Density estimates are used to determine the threshold spread rate (or surface windspeed) used to determine the likelihood of active crown fire.

Canopy Bulk Density is a difficult concept to apply to crown fire predictions. This image shows that CBD varies with height above ground.

This graph, also displayed in the Crown Fire section, displays the threshold surface 20ft windspeed, or Crowning Index, necessary for producing active crown fire given a specific canopy bulk density.

Crowning Index. Based on Rothermel crown fire spread model, canopy bulk density can be related to the windspeed required to sustain crown fire.