Fuels Planning: Science Synthesis and

Integration

Forest Structure and Fire Hazard Fact Sheet: 1

Forest Structure and Fire Hazard

Overview

United States

Department

of Agriculture

Forest Service

Rocky Mountain

Research Station

Research Note

RMRS-RN-22-1-WWW

September 2004

Overview

Many managers and policymakers guided by the National Environmental Policy

Act process understand that fuel treatments for reducing the size and severity of

wildfires must be based on scientific principles. The Forest Structure and Fire

Hazard Team is providing the science to assist this kind of decisionmaking in

dry forest ecosystems in National Forests and other public lands of the Western

United States. Because of past management and policy decisions, current forests

have denser canopies, more fire-intolerant species, and fewer large trees. These

conditions, coupled with fuel accumulations at higher than historic levels, increase the probability of surface fires developing into crown fires because understory ladder fuels lower the effective canopy base height of the stand.

Estimating Fire Hazard

Fire hazard reflects the potential magnitude of fire behavior and effects as a

function of fuel conditions. Understanding the structure of fuelbeds and their

role in the initiation and propagation of fire is the key to developing effective

fuel management strategies. Thus, based on forest structure, fuels have been

traditionally characterized as crown fuels (live and dead material in the canopy of

trees), surface fuels (grass, shrubs, litter, and wood in contact with the ground

surface), and ground fuels (organic soil horizons, or duff, and buried wood). A

more refined classification separates fuelbeds into six strata: tree canopy; shrubs/

small trees; low vegetation; woody fuels; moss, lichens, litter; and ground fuels

(duff). Modification of any fuel strata (layer) has implications for fire behavior,

fire suppression, and fire effects.

Visualizing Fuel Treatments

The scenic impact of fuel treatments across large landscapes can be visualized

with management tools such as the Landscape Management System, which uses

stand inventory data (species, height, diameter, stem density), geospatial data,

and forest growth models to project forest vegetation succession and changes in

landscape pattern.

The use of other analytical tools can also be effective in scheduling fuel treatments over time. For example, the Forest Vegetation Simulator (FVS) and the

Historical Present

Forest Structure and Fire Hazard

Team Leader

David L. Peterson

USDA Forest Service

PNW Research Station

400 N. 34th Street, Suite 201

Seattle, WA 98103

Fuels planning: Science synthesis and

integration, an interagency research/

management partnership to support

the Ten-Year Fire Plan, led by Russell

T. Graham, RMRS, and Sarah M.

McCaffrey, NCRS.

Synthesizing

Scientific Information

for Fire and Fuels

Project Managers

Pacific Northwest

Research Station

The information for this

fact sheet was provided by

Kelly OíBrian, Fire and

Mountain Ecology Lab,

University of Washington.
The Fuels Planning fact sheets are based on preliminary findings. Information from fact sheets will be synthesized in an upcoming publication.

Fire and Fuels Extension of FVS can be used to quantify vegetation and fuel succession following fire or fuel

treatments. Scheduling of fuel treatments will vary by

species, elevation, aspect, climatic zone, and soil fertility. Broad spatial perspectives and tools are the key to planning and implementing management for a fire-resilient

landscape.

Managing Forests to Reduce Crown Fires:

The Role of Silviculture

The major goals of fuel reduction treatments are to reduce fireline intensities, reduce the potential for crown

fires, improve opportunities for successful fire suppression, and improve the ability of forest stands to survive

wildfire. Thinning and prescribed fire target crown, ladder, and surface fuels of a forest stand or landscape to

modify vegetation in each stratum.

Thinning can reduce the probability of crown fire spread,

because canopy and ladder fuels are modified by treatments that effect crown classes, stand basal area, or

canopy bulk density. Thinning may be expensive and

poses a challenge for handling large amounts of woody

material, much of which may be unmerchantable. Prescribed burning is a less precise management tool, although it can be highly effective at reducing surface fuels, and in some cases ground fuels. In some cases it can

be used to reduce stem density and ladder fuels by killing

smaller trees. Thinning followed by prescribed burning reduces canopy, ladder, and surface fuels, thereby providing

maximum protection from severe fires in the future.

When, where, and how fuels are treated requires the

combined skills of fire managers, silviculturists, and other

experts. Individual stand treatments will have maximum

effectiveness only if they are planned in the context of

the broader landscape. The complex job of planning and

implementing fuel treatments requires the best available

scientific informationóthe Forest Structure and Fire

Hazard Team will provide that information to resource

managers and the general public in order to expedite

fuels management in the United States.

Forest Structure and Fire Hazard Fact

Sheets

Look for other fact sheet topics from the Forest Structure and Fire

Hazard Team with information about fire hazard, visualization,

silviculture, uncertainty, and larger scale treatments.

Fuels Planning: Synthesis and Integration

This fact sheet is one in a series being produced as part of a larger

project supported by the USDA Forest Service to synthesize new

knowledge and information relevant to fire and fuels management.

Fact sheets address topics related to stand structure, environmental

impacts, economics, and human responses to these factors. Information in the fact sheets is targeted for the dry forests of the Inland

West, but is often applicable across broad regions of the country.

For more information, please visit our Web site at:

www.fs.fed.us/fire/tech_transfer/synthesis/synthesis_index