Protecting Relatively

Uninfested Lands:

Reducing 

Weed Spread 

Following Fire

Jerry Asher, Bureau of Land Management, Portland, OR; Steve Dewey,

Utah State University, Logan, UT;

Curt Johnson, USDA Forest Service,

Ogden, UT; Jim Olivarez, USDA 

Forest Service, Missoula, MT

This Resource Note is adapted from

the December 2000 issue of TechLine,

(published by Ag West Communications.) summarizing several studies

and successful post–fire management

programs.

Used with permission of the 1999

California Exotic Pest Plant Council

Proceedings.

Wildland fire is a naturalprocess that often helps to

maintain or improve the health

and productivity of native plant

communities. However, when

invasive exotic plants are involved,

fires burn in an unnatural situation. There are two purposes to

this presentation. The first is to

show how weeds often proliferate

following wildland fire. The second is to discuss how reducing

post-fire weed spread is one of the

best ways to keep relatively uninfested land from becoming seriously

infested. It is common knowledge

that various plants respond differently to fire. However, all too often

weeds rapidly infest burned areas

frequently causing vast and permanent damage. Therefore the intent

of this presentation is to increase

the awareness about this problem

along with providing some

recommendations—with every

intention to support appropriate

prescribed fire efforts.

How vulnerable are typical

wildland sites following fire?

Factors like an ideal seed bed,

reduced competition from native

plants and increased nutrients

released by the fire all combine to

make conditions ideal for weed seed

to germinate and flourish following fire. With conditions ideal,

how much weed seed is likely to

be available on any burned site?

There are about 70 million acres of

noxious weeds, primarily on wildlands, in the 11 western states (outside of Alaska). Consequently there

are roughly 70 million acres of weed

seed produced every year! Much of

that seed is making its way to relatively uninfested land by wind, water,

wildlife, livestock, people and equipment. Therefore, after wildland fire in

a previously uninfested area, there is a

high likelihood for both ideal conditions for weed establishment, and the

presence of weed seed. Furthermore,

biennial and perennial weeds, already

present in the fire area, commonly

sprout from buds or crowns. Squarrose knapweed, diffuse knapweed and

rush skeleton-weed for example often

re-sprout, flower and set seed within

six weeks of a fire—while most other

vegetation is dormant waiting another season to produce seed. This

almost immediate seed production

following fire gives the weeds yet

another advantage.

Examples of weed spread

following fire

Every year we learn more about the

challenge of reducing the spread of

invasive wildland weeds. A multitude

of post–fire photographs in many

western states make it clear that weeds

frequently invade and dominate plant

communities following fire, sometimes on a large scale. For example,

in the Bureau of Land Management Sand Butte and adjoining

Wilderness Study Areas in Idaho,

considerable weed surveillance and

successful control of leafy spurge

had been underway for many

years. A 200,000-acre wildfire

burned over the area in 1992.

Rush skeletonweed was not known

to exist there until 1995, when a

few rush skeletonweed plants were

found and controlled. In 1996

another wildfire, also about

200,000 acres, burned the entire

area again. A preliminary detection

survey in 1997 found serious rush

skeletonweed infestations widely

scattered within a 60, 000 acre area

of the burn.

In a research example from northern Utah, wildfire increased

squarrose knapweed abundance

by 50% to 120% within just two

years. Control of squarrose knapweed from herbicide applied in

the first fall after a summer burn

was 98% to 100% effective, while

the same herbicide treatment

achieved only 20% control or less

in adjacent non-burned areas.

Not only did this study show that

invasive weeds can increase dramatically after a fire, but it also

shows that post-fire herbicide

application is a unique window of

opportunity for effective control.

Recommendations

With weeds spreading at about

4,600 acres per day on western

federal lands alone (outside of

Alaska), the overarching goal

becomes keeping relatively uninfested land from becoming seriously infested. Capitalizing on the

opportunity to prevent weed

spread after fires is cost effective

and efficient.

NO. 52 DATE 06/27/01

Range

Forestry
Readiness and Post-fire 

Vigilance:

1. At the earliest possible time,

hopefully before the fire season,

ensure that the NEPA process is

adequate to cover timely application

of herbicides—if needed anywhere

on the landscape. The proper process

needs to be in place so an environmental analysis update or amendment or whatever documentation is

needed does not unduly delay the

application of herbicides in order to

avoid weed seed set after a fire.

2. Establish procedures that minimize

the transport of weeds into or within

a proposed fire or burned area.

3. Include existing, or consider

involving new cooperators. Weed

management efforts have a higher

probability of success when adjacent

landowners, public land users, agencies, universities, or other interested

people are participating.

4. After fires, when weeds begin to

“show life” either starting from seed

or sprouting from crowns or roots of

existing plants, there frequently are

outstanding opportunities to control the weeds. Weeds are usually

easier to find for hand control or

other mechanical techniques, and

herbicide application is more effective because weeds are no longer

protected by non-target vegetation

or debris. Capitalize on this rare

opportunity before the weeds have a

chance to produce seed.

5. Build the cost of weed management caused or encouraged by the

disturbance of the fire into fire rehabilitation plans. In 1998 the Bureau

of Land Management, Forest Service,

Fish and Wildlife Service and the

Park Service were given new authority to use fire rehabilitation funds to

control weeds following wildfire,

including weed detection and control

in subsequent years. Where rehabilitation plans are not intended, use

creativity and perseverance to ensure

that invasive weeds get the priority

they deserve.

6. Approximately one month after

any fire, survey the entire fire area

for signs of new or sprouting weeds.

Repeated surveys will be needed,

with the frequency and intensity

guided by local conditions.

7. Develop and implement a strategy to control the weeds including follow-up detection and

treatments for a few years until

the populations are completely

controlled or eradicated.

Prescribed fire planning:

Before burning evaluate the potential for increased weed populations

and consider the following:

1. Check existing weed maps and

visit with local weed experts. Then

survey the entire proposed burn

area for weeds. If a few weeds have

been on the site for a year or more

it is likely that thousands of

unseen seeds are in the ground

ready to germinate.

2. Check adjacent land for weeds

that may become a seed source

following the burn. These areas

may provide weed seed to the

burn area via transport by people,

livestock, wildlife, wind, water,

vehicles or other equipment.

3. Enlist the advice of agency

weed coordinators, extension

agents, Department of Agriculture or county weed supervisors

regarding plans to minimize the

increase in weeds. Where possible,

time the burn to reduce seed production of existing weeds. Make

sure that equipment, vehicles and

personnel do not bring weed seed

in with them from other areas.

4. Ensure that the appropriate

NEPA process/requirements for

weed control are addressed before

the fire to avoid any delays in timely application of herbicides in the

event they are needed.

5. Keep a log of weed management

activities so you can share your

experiences with others.

Level of Urgency:

Nature often helps put out fires;

nature does not help “put out” weeds.

Fires are often very beneficial, but

weeds are not beneficial. If and when

there are negative impacts from fire,

they are usually short-term, whereas

impacts from weeds are long term

and often permanent. 

Therefore, new infestations or small

burned infestations poised to proliferate out-of-control, truly constitute a

state of biological emergency! When

preparing NEPA documents, keep

that concept in mind regarding the

emergency nature of controlling

weeds following fire before they have

a chance to set seed.

In conclusion, we must keep relatively uninfested land from becoming

seriously infested. Future generations

deserve to inherit healthy, productive

wildlands, not vast landscapes infested with noxious weeds that are unfit

for people or wildlife.

Range

Resource Notes are intended to be early

announcements of technical and informational topics for

Bureau of Land Management personnel and some of their customers.

Information in this Resource Note is based on the opinion and

experience of the author and has not been peer-reviewed. Conclusions

and opinions expressed herein do not

necessarily represent those of BLM. Use of trade names does not

imply U.S. Government endorsement of commercial products.

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