Fuels Planning: Science Synthesis and

Integration

Environmental Consequences Fact Sheet: 7

Fire and Weeds

United States

Department

of Agriculture

Forest Service

Rocky Mountain

Research Station

Research Note

RMRS-RN-23-7-WWW

December 2004

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

Environmental Consequences

Team Leader

Elaine Kennedy Sutherland

USDA Forest Service

Rocky Mountain Research Station

Missoula, MT

Steve Sutherland

USDA Forest Service

Rocky Mountain Research Station

Fire Sciences Laboratory

Missoula, MT

The Weed Problem

There are nearly 3,500 exotic plant (nonnative introduced) species in the United States. Of

these species, 300 have been placed on State or Federal noxious weed lists because of

their invasive potential. Currently, weeds infest about 100 million acres and are expanding

at the rate of 3 million acres per year. Weed infestations cause an economic loss of $13

billion per year even though $9.5 billion per year is spent on weed control measures. In

addition to these economic costs, weeds are replacing native species, altering native plant

and animal communities, affecting ecosystem health and function, threatening biodiversity

and Threatened, Endangered, and Sensitive (TES) species, altering fire behavior and fire

regimes, and reducing wildland productivity.

Where Are Weeds Found?

Weeds exploit disturbed sites. These are areas that have reduced competition, exposed

mineral soils, and high light and nutrient levels. If weeds are present before the disturbance,

or weed seeds arrive after disturbance, weeds will commonly increase on disturbed areas.

What Promotes Weed Invasions?

Most activities that disturb soil and increase light levels create favorable conditions for

weed invasions.

Wildfire

Because of past land management activities

and fire suppression policies, fuels have been

accumulating for the past century and have

resulted in some unusually large, severe, and

uncontrollable wildland fires in many areas

of the dry forest type. These fires result in

increased exposure of mineral soil, reduced

plant competition, and increased light and

nutrient levels—conditions that are favorable

to exotic weed species. In addition, fire can

reduce or eliminate biological control

(biocontrol) agents previously released to control invasive species. By creating conditions

favorable to the rapid expansion of exotic

weeds and removing existing barriers to that expansion, wildfires can set the stage for an unprecedented invasion of new weed species and expansion of established weed species.

Orange hawkweed in a postfire area (photo

credit: Steve Sutherland).

In addition to the direct effect of wildfire on weeds, many fire-related management

practices such as fire suppression, emergency rehabilitation of burned areas, and salvage

logging can also result in habitat disturbance that promotes weed invasion and expansion.

Fire-Related Management Activities
The Fuels Planning fact sheets are based on preliminary findings. Information from fact sheets will be synthesized in an upcoming publication.

Environmental Consequences Fact

Sheets

Look for fact sheet topics from the Environmental Consequences

Team including information about the effects of fire behavior and

alternative treatment strategies, Wildlife Response Model, weed responses, riparian systems, soil erosion, restoration objectives, treated

spaces, the Fire Effects Information System (FEIS), and the First

Order Fire Effects Model (FOFEM).

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

The creation of fire lines (whether by hand or dozer), helispots,

and heliports removes competing vegetation, exposes mineral soil, and increases light levels. If the fire is large, then fire

suppression resources may come from across the nation or

from outside the United States, and may bring new weed

propagules with them. Fire fighters, fire equipment, dozers,

trucks, and helicopters can all transport weed propagules to

fire lines, helispots, and burned areas. The establishment of

fire camps also disturbs soil. Weeds already existing in these

camps can act as source populations for the introduction of

new weed species into the burned areas.

Because of concern about effects of high-severity fires on

soil productivity, watershed response, and downstream sedimentation, the Burned Area Emergency Rehabilitation (BAER)

program was established to reduce the loss of soil and onsite

productivity, reduce the deterioration of water quality, reduce

the threat of flooding, and reduce the threat to life and property. While BAER treatments may be effective in reducing soil

erosion and flooding, they may have the unintended consequence of promoting weed invasion and expansion. For example, contour felling is sometimes implemented to stop sheet

erosion and trap sediment, but the logs can also act as seed

traps for weedy species. The combination of exposed mineral soil, increased soil moisture, and high number of weed

seeds associated with contour felling can lead to localized,

dense populations of weed species that can colonize the adjacent burned areas.

Salvage-logging after wildfires can provide an economic stimulus to the surrounding community. However, salvage logging

can also introduce new weed species, transport weed

propagules to weed-free areas, reduce native plant competition, expose mineral soil, and increase light levels. All of these

factors can promote weed invasion and expansion.

Canada thistle, 1 month postfire (photo credit:

Steve Sutherland).

Fuels Reduction

Fuels management appears to be the best method to reduce

fire hazard and restore natural ecosystem processes, at least in

plant communities with historically frequent, low-severity fire.

Fuels reduction will still involve the use of fire whether as

prescribed fire, wildland fire use, or burning in conjunction

with mechanical thinning. Like wildfire, prescribed fires result

in increased bare soil, reduced plant competition, and increased

light and nutrient levels—conditions that are favorable for

exotic weed species.

Incorporating Weed Management Into Fuel

Treatment Activities

Because the difficulty and cost of weed control increase rapidly with size of weed infestation, it is imperative that weeds

be controlled as soon as possible. If potential impacts of

fire-related management activities on weeds are known, then

weed control measures can be part of the fuel treatment plan,

and weed populations can be stopped when they are small.

For More Information

Brown, James K.; Smith, Jane Kapler, eds. 2000. Wildland

fire in ecosystems: effects of fire on flora. Gen. Tech. Rep.

RMRS-GTR-42-vol. 2. Fort Collins, CO: U.S. Department

of Agriculture, Forest Service, Rocky Mountain Research Station. 257 p.

Fire Effects Information System. [Online]. U.S. Department

of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, Missoula, MT. (2003 October).

Available:http://www.fs.fed.us/database/feis/ [09/07/04].

Galley, K. E. M.; Wilson, T. P., eds. 2001. Proceedings of the

invasive species workshop: the role of fire in the control and

spread of invasive species. Misc. Publ. No. 11. Tallahassee,

FL: Tall Timbers Research Station.

Goodwin, K.; Sheley, R. 2001. Integrated noxious weed

management after wildfires. Bozeman, MT: Montana State

University.