Risk of Cheatgrass

Invasion After

Fire in Selected

Sagebrush 

Community Types

By William G. Ypsilantis, 

Soil Scientist, BLM, National 

Science and Technology Center

Background

The recent emphasis on restoring

natural fire processes to the land has

created considerable interest and

opportunities for the use of prescribed burning to treat sagebrush

steppe ecosystems. Prescribed burning is a management tool that can

be used to improve or maintain the

health and productivity of these plant

communities. The potential exists,

however, for invasion and dominance

of prescribed burn or wildfire sites

by cheatgrass (Bromus tectorum L.).

I discuss here the risk of cheatgrass invasion in Wyoming big

sagebrush (Artemisia tridentata

Nutt. ssp. wyomingensis) and

mountain big sagebrush (Artemisia

tridentata Nutt. ssp. vaseyana) ecological sites, with a brief reference to

threetip sagebrush (Artemisia tripartita Rydb.) sites. Additionally, I outline some recommended practices for

reducing these risks.

The Problem

Cheatgrass is an exotic annual and,

occasionally, biennial grass native to

Eurasia and the Mediterranean. It was

probably introduced in the Intermountain West in the 1880s in

impure grain seed. By 1981, it was

reported to be the dominant plant on

more than 40.5 million ha (100

million acres) in the Intermountain

West. Recent extensive wildfires in

the Great Basin have greatly increased

the areas dominated by cheatgrass. 

Cheatgrass-dominated sites result in

reduced forage on critical winter

rangeland for mule deer (Odocoileus

hemionus), American pronghorn

(Antilocapra americana), and other

game animals. Habitat for sage

grouse (Centrocercus urophasianus)

brood rearing and cover is lost.

Cheatgrass has overtaken more than

50% of the Snake River Birds of

Prey National Conservation Area,

reducing the birds of prey food base

and thus the numbers of birds.

Competition with sensitive plant

species for water and nutrients is

increased, and a resultant increased

fire frequency can eliminate these

plant species from a site. Cheatgrass

can dramatically decrease the amount

of nitrogen available to perennial

plants, since it directly uptakes and

depletes nitrogen from the soil. It

can also shade out biological soil

crusts that fix nitrogen.

Because of its flammability, cheatgrass greatly increases the fire hazard

on a site. It can change the fire

recurrence interval from the natural

20 to 100 years for sagebrush grassland ecosystems to 3 to 5 years for

cheatgrass-dominated sites. The rate

of spread, size, and frequency of fire

also increase. Cheatgrass fires spread

rapidly and may extend into nearby

stands of native vegetation, reducing

the cover of valuable perennial

species. Cheatgrass dominance

increases the occurrence of fire earlier in the growing season, which negatively affects native herbaceous

species. The frequent cycle of large

fires eliminates native shrubs, forbs,

and perennial grasses and results in a

self-perpetuating stand of cheatgrass.

Frequent fires remove all protective

plant and litter cover, making the

site susceptible to accelerated wind

and water erosion and high runoff.

Competitive Characteristics

Cheatgrass is a vigorous and

opportunistic competitor. After

fall germination, its finely divided,

fibrous roots grow rapidly and are

well developed by the time spring

growth begins. The root system

quickly occupies the surface soil and

takes up most of the soil moisture,

depriving species that develop more

slowly. Cheatgrass is a prolific seed

producer, yielding as many seeds as

448 kg/ha (400 pounds/acre). The

seed is normally high in viability

and germinates within a few days

under favorable conditions. Although

less than 13% of seed survives until

the following winter, a few seeds may

survive for as long as 5 years. Cheatgrass monocultures have low vesicular-arbuscular mycorrhizal (VAM)

fungal populations (beneficial fungi

that penetrate and colonize the root

of a plant, funneling nutrients back

to the plant); this increases the difficulty of reestablishing sagebrush and

native bunch grasses that require

these mycorrhizae.

Cheatgrass is capable of adapting to

new habitats. During the last two

decades, cheatgrass has spread

beyond the sagebrush ecosystem

into salt desert communities,

mountain brush types, and open

conifer—especially Ponderosa pine

(Pinus ponderosa)—woodlands.

Cheatgrass has been identified as the

C3 species most positively responsive to increased CO2 and thus

capable of benefiting from global

atmospheric trends.

Cheatgrass completes its life cycle in

spring, before the summer dry

weather begins. Its complete drying

and fine structure make it extremely

flammable. Frequent fires favor

cheatgrass by eliminating perennial

vegetation. Its seeds survive in the

unburned organic material on a site,

either on or in the mineral soil.

After fire releases a flush of available

nitrogen, cheatgrass utilizes it before

perennial grasses have a chance to

use it. Rapid growth and vigorous

NO. 63 DATE 02/04/03

Range

Soils/geology

Resource Note 63

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reproduction ensure cheatgrass

dominance in the postburn stand.

Invasion Risk in Selected

Sagebrush Community Types

Wyoming big sagebrush ecological

sites are warm and dry, and therefore have a high risk of cheatgrass

invasion. Mountain big sagebrush

sites have the lowest risk of cheatgrass invasion due to lower winter

temperatures and more moisture

availability for perennial grasses.

Threetip sagebrush sites have intermediate risk in susceptibility to

cheatgrass invasion.

Recommendations

• Minimize burning on the

Wyoming big sagebrush range

sites. 

• Don’t burn on southern and

western aspects. 

• Burn threetip sagebrush sites only

when adequate perennial grass

exists to recolonize the site.

• Concentrate prescribed burning

on the cooler, moister, mountain

big sagebrush sites. 

• Avoid burning on steep, granitic,

drought-stricken sites—especially

those with southern and western

aspects. They tend to ravel, and

they maintain sparse perennial

grass cover even under good ecological conditions. 

Open pine stands have a moderate

to high risk of cheatgrass invasion,

depending on elevation. Closed

forested sites have a low risk of

cheatgrass invasion after prescribed

burning, as long as there is adequate

postfire overstory or understory

vegetation to shade it out.

Prefire assessment and postfire monitoring are important. Inspect all

proposed burn sites for the presence

of cheatgrass, and look at adjacent

areas that could be a seed source.

Cheatgrass is easy to identify from a

long distance when it is in the purple stage just before senescence, usually in the latter part of June. The

soil surface layer should also be

examined for seed. Chemically treat

infested areas if possible, or select

alternative burn sites. Assess the adequacy of preburn perennial grass

cover. Perennial grasses should be

vigorous, with at least one plant per

square meter. Postfire monitoring

should note the response of native

vegetation to the burn and to the

location, size, and density of cheatgrass invasions.

Burning tends to increase palatability of native forage and acts as a

magnet for grazing animals. Burn an

area large enough to not be easily

overgrazed by a few livestock or elk

(Cervus canadensis). When conducting smaller test burns, protect the

burn area from grazing with electric

fencing. On larger burn areas, use a

mosaic burn pattern.

Instruct firefighters in precautions

to avoid spreading cheatgrass by

removing seeds from clothing and

equipment transported into burn

areas. Chemically treat helipads and

fire lines infested with cheatgrass.

It is important to maintain good

perennial grass cover on prescribed

burn areas. Idaho fescue (Festuca

idahoensis Elmer) is susceptible to

damage from burning. Use prescriptions that are least harmful to Idaho

fescue. Spring burns should be in

March, before Idaho fescue breaks

dormancy; however, fall burning

during the cool conditions in late

September or October is recommended. Some resource specialists

recommend burning late enough

that fescue will not break dormancy

before winter sets in and freezes the

burn areas. Other ecologists recommend not burning once fescue has

broken dormancy in response to fall

rains and is actively growing. California BLM personnel use sweet

clover (Melilotus spp.) as a cover

crop for the perennial grasses.

A recommended practice is to rest

a planned burn area for one growing season before burning, to

build up adequate fuels. However,

the Fire Effects database

(http://www.fs.fed.us/database/feis/)

recommends allowing grazing for

1–2 years before burning Idaho

fescue to reduce mortality by eliminating some fuel buildup above

the root crown. Burned areas should

be rested at least 2 years to allow full

recovery of perennial grasses. Longterm postfire management is important in maintaining perennial grasses

and reducing cheatgrass invasion.

Biological soil crusts (e.g., microbiotic crusts, cryptogams) help deter

cheatgrass invasion. The avoidance

of livestock grazing on areas with

good crust cover, during the dry season when they are most susceptible

to damage, is recommended. Don’t

burn just for burning’s sake. Prescribed burn goals and objectives

should be ecologically based and

achievable.

Contact

William G. Ypsilantis, Soil Scientist

National Science and Technology

Center

Denver Federal Center

Building 50

P.O. Box 25047

Denver, CO 80225-0047

Phone: 303-236-3404

Fax: 303-236-3508

Email: Bill_Ypsilantis@blm.gov

Range

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which are posted on this

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contained in this Resource Note 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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(Debbie_Harris@blm.gov)

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(Brian_St_George@blm.gov)

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Thank you for your interest in Resource NoteS.

Resource Note 63

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