Prepare to Handle

Post-fire Weed

Explosion Within

Two Years of a Fire

By Charles Henry

TechLine Editor

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.

The rangeland management

specialists on the Helena

National Forest don’t play with

fire, but they do use prescribed

burns to supplement their invasive species management and

learn more about fire’s effects on

weeds. Jay Winfield, rangeland

specialist on the Helena and Lincoln Ranger Districts in Montana,

says they know that fires promote

weed growth and spread. Forbs

usually come back first after a

fire and most invasives are

forbs. “We see a doubling in

density of some species such as

Dalmatian toadflax.”

“You must be ready to handle

this explosion and do the control work within two years of a

fire because this window of

opportunity is when your postfire herbicide treatments are

most effective.” In recent trials,

Helena range specialists treated

Dalmatian toadflax in the fall

with Tordon* 22K herbicide at

rates from 0.25 lb per acre to

0.5 lb per acre. The following

spring they burned the area

and repeated the herbicide

applications. “On shallow soils

inhabited with blue bunch

wheat grass, we achieved good

control. Heavier soils vegetated

with rough fescue displayed

excellent control results,”

Winfield explains.

“The Cave Gulch fire burned

during the summer of 2000 on

the Helena National Forest. This

fire burned with high intensity

with lethal effect to most of the

vegetation in the path of the fire.

The Cave Gulch fire burned into

this area that had been prescribed burned and chemically

treated within the past two years.

Once the fire perimeter reached

the previously managed area, the

fire burned with reduced intensity

and at a much slower rate of

spread. The fuel reduction area

actually stopped the Cave Gulch

fire in some areas, forcing the fire

to burn around the previously

treated area. So we look at prescribed fire and the wildfires as

an opportunity to get ahead of

weeds, but you have to be prepared to follow up with aggressive

herbicide treatments following

fire. And you must plan ahead

to reduce the role fighting

wildfires play in spreading invasives,” he explains. Following are

operational techniques that will

minimize invasive species spread:

Pre-fire Planning:

1. Pre-establish base camp locations for each mountain range

and coordinate these locations

with the forest service, state

forests, private landowners, the

Department of Agriculture, and

Department of Natural Resources

and treat these accordingly.

2. Pre-establish heli-bases and

heli-landing staging areas before

the fire season. In timber, these

sites are limited, so they are easy

to designate.

3. Monitor and manage invasive

species infestations on these sites

so they are weed-free before they

are used to fight fires. “On the

Boulder Hill fire this past summer, spotted knapweed was scattered throughout base camps on

U.S. Forest Service and private

properties,” Winfield states.

“All base camps power-wash

equipment, but this is somewhat futile if you are washing

in weedy areas.”

4. Flag off high-infestation,

high-risk areas on fire maps.

5. It’s critical to conduct invasive species inventories by

mountain range or geographic

area, then monitor and treat

these areas before they burn.

6. Target your education efforts

to experienced fire fighters

regarding weed ID and the

weeds’ effects so they don’t

spread species such as houndstongue on their clothing and

packs. Direct these fire fighters

to then inform supplemental

crews about weeds.

During the Fire:

1. If possible, determine the

intensity and duration of the

fire. This helps predict where

weeds might occur after a fire.

Fires change the hydrophobic

condition of the soils so they

shed water more because the

NO. 54 DATE 10/30/01

Range

Forestry

*Trademark of Dow AgroSciences, LLC

Tordon 22K is a federally Restricted Use Pesticide
organic bonding capability is

reduced. After a fire, more sunlight reaches the soil and the

litter component that aids in

moisture retention is removed.

These conditions predict high-risk

areas for weeds after a fire.

2. Make fire management teams

aware of where you have treated

weeds, made biological releases,

or performed other weed management. At times they can move

fire lines away from and minimize soil disturbances in these

areas if they are informed ahead

of time.

Post-fire Management:

1. Verify your mapping and step

up your monitoring after a fire

so weed outbreaks are caught

early and their management cost

is covered in your budget.

2. Increase treatments if possible.

The first two years are critical

after a fire. 

3. Re-vegetation work must go

hand-in-hand with weed treatments.

4. If non-native grass species

already exist on a site, they

may be the best choice for initial

re-vegetation work since they are

more competitive than many

native species. Decisions should

be made site by site after field

inspection.

5. Monitor all treatments and

plan for re-treatments as needed.

6. Minimize human disturbances such as ATVs, snowmobiling, and even non-motorized

uses to lessen weed spread and

introduction from the outside. 

7. Educate the public to avoid

recreating in burned areas so

they don’t undermine weed

treatments and re-vegetation

work.

Range

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