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Fuels: Canopy Fuel Characteristics

  1. Canopy Cover-Percentage or Class
  2. Stand (Canopy)-Height-ft or m
  3. Canopy Base Height-ft or m
  4. Canopy Bulk Density-kg/m3 or lb/ft3

Canopy Cover - Percentage or Class

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

The scale illustrates representative CC percentages and ranges within each cover class.

Image
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

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Stand (Canopy) Height-feet (ft) or meters (m)

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

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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 CBH is used in the Crown Fire Initiation model.

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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.

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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). CBD estimates are used to determine the threshold spread rate, or surface wind speed, used to determine the likelihood of active crown fire.

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

The following graph, also displayed in the Crown Fire section under Crown Fire Initiation and Propagation, displays the threshold surface 20 feet wind speed or Crowning Index, necessary for producing active crown fire given a specific canopy bulk density.

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

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The updated NWCG Standards for Airtanker Base Operations (SABO), PMS 508 standardizes operations and procedures at interagency airtanker bases to ensure safe, efficient, and effective operations in support of interagency goals and objectives.

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NWCG Standards for Airtanker Base Operations, PMS 508

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The 2025 Core Component Module Package for RT-130, Wildland Fire Safety Training Annual Refresher (WFSTAR) and the 2024 Fire Year in Review are now available on the NWCG website. The 2025 Core Component Module Package provides all content needed to deliver RT-130.

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2025 Core Component Module Package

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NWCG Wildland Urban Interface Mitigation Field Guide, PMS 053 

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The NWCG Standards for Wildland Fire Module Operations, PMS 430 standardizes procedures and expectations for Wildland Fire Modules (WFMs). These standards are to be used by staff, supervisors, specialists, and technicians for planning, administering, and conducting WFM operations. These standards will also be used as a measure of WFM qualifications, capabilities, and expected performance, for both Type 1 and Type 2 WFMs.

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NWCG Standards for Wildland Fire Module Operations, PMS 430