Fuels Planning: Science Synthesis and

Integration

Forest Structure and Fire Hazard Fact Sheet: 4

Role of Silviculture in Fuel

Treatments

United States

Department

of Agriculture

Forest Service

Rocky Mountain

Research Station

Research Note

RMRS-RN-22-4-WWW

September 2004

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

What Is a Fuel Treatment?

A fuel treatment is any management operation implemented to reduce forest

fuel accumulation. The principal goals of fuel treatments are to reduce fireline

intensities, reduce the potential for crown fires, improve opportunities for successful fire suppression, and improve forest resilience to forest fires. Fuel treatments typically target canopy, ladder, and surface fuels to modify vegetation in

each stratum. Thinning and prescribed fire target different components of the

fuelbed of a given forest stand or landscape.

Types of Fuel Treatments

ThinningóThinning is a common silvicultural practice implemented to reduce

canopy and ladder fuels. Canopy and ladder fuels are modified by thinning operations that target stem density, stand basal area, canopy base height, or canopy

bulk density. There are many types of thinning operations. However, thinning

from below (or ìlow thinningî) is the most common type of thinning used for

reducing fire hazard. Thinning from below removes intermediate and suppressed

trees from the lower crown strata. This thinning type can be effective at reducing the probability of crown initiation and fire spread and is precise in that

manager-designated trees are targeted and removed from the fuelbed. A sample

prescription would be to remove all trees under 9 inches in diameter.

Surface Fuel TreatmentsóSurface fuels, such as woody fuels and litter created from falling branches and thinning operations, can be modified by prescribed fire or other fuel treatments such as pile-and-burn, lop-and-scatter, or

crushing and chopping (mastication). The most common operation used to reduce surface fuel loads is prescribed burning. Prescribed burns affect potential

fire behavior by reducing surface fuel continuity and loadings, thereby reducing

fireline intensity and the likelihood of crown fire initiation. Prescribed fires may

also raise live crown base height of a stand by scorching the lower branches of

individual trees.

The type and sequence of fuel treatments depend on the amount of surface fuel

present; the density of understory and mid-canopy trees; the long-term potential effects of fuel treatments on vegetation, soils, and wildlife; and short-term

potential effects of smoke production. In forests that have not experienced fire

for many decades, multiple fuel treatments are often required. Thinning followed

by prescribed burning reduces canopy, ladder, and surface fuels, including fuels

that are created by the thinning operation itself. Given current accumulations

of fuels in some stands, multiple prescribed fires as the sole treatment or in

combination with thinning may be needed initially, followed by long-term maintenance burning or other fuel reduction techniques to reduce crown fire hazard.

The information for this fact

sheet was provided by Morris

Johnson, Pacific Northwest

Research Station, USDA Forest Service
The Fuels Planning fact sheets are based on preliminary findings. Information from fact sheets will be synthesized in an upcoming publication.

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

Fuel Treatment Challenges

Fuel treatments are most effective in areas that do not

have steep slopes, are not typically subjected to extreme

winds, and are accessible by firefighting equipment and

personnel. A lack of accessibility may limit the possibility of fuel treatment in wilderness and other roadless

areas. Areas with steep slopes are also difficult to treat

because of the increased challenges and costs of thinning (removing logs and surface fuels), and the increased

risk of escaped fire due to the interaction of slope and

fire behavior. The presence of threatened or endangered

species may also preclude some types of fuel treatments.

Potential secondary effects may also pose management

challenges. Prescribed fires may kill individual trees and

clumps of trees, which may increase long-term fuel

loads. Prescribed fires also create smoke, which decreases

air quality in local communities, and chars trees, which

creates a potentially undesirable aesthetic loss for some

locations with high visitor use. When making decisions,

these potential negative outcomes must be weighed

against the potential long-term benefits of fuel treatments for restoring fire in Western ecosystems.

After thinning

from below.

Forest stand before

treatment.

After thinning and

prescribed fire.