20 Agricultural Research/March 2003

uring the summer of 2000, awildfire blazed through 500 hect-ares of grazingland at the Agri-cultural Research Service’s U.S.

Sheep Experiment Station (USSES) nearDubois, Idaho. That fire has sparked newresearch on the effects that grazing ani-mals have on rangeland biodiversity andits recovery after wildfires.

Currently, there is much debate amongscientists and others about how grazingaffects diversity of plant species grow-ing in grazed areas. Some say grazing isharmful; others claim it neither helps norhurts; and still others insist it can be ben-eficial if managed correctly. But littledata has actually been collected untilnow.

“When the 2000 wildfire burnedthrough the station, it destroyed half ofa long-term study,” says Gregory Lewis,USSES’ research leader. For more than50 years, USSES scientists had beenanalyzing the effects of grazing atdifferent times of year and the effectsthese grazing periods had on the plantcommunity.

During the long-term study, somepastures were grazed only in the spring,others only in the fall. The controlpastures weren’t grazed at all, and after50 years, they had been taken over by aheavy canopy of sagebrush. The fall-grazed pastures had less sagebrush andmore perennial forbs, while the spring-grazed pastures had less forb cover andincreased grass and sagebrush.

Forbs are broadleaf plants that don’thave woody stems and include perenni-al plants such as arrowleaf balsamrootand tapertip hawksbeard.

Rangeland scientist Steven Seefeldtsays that when the 2000 fire roaredthrough, the ungrazed pastures fared theworst. According to Seefeldt, “Therewasn’t a green thing left. The fire took itall to the ground.”

The spring-grazed plots fared a littlebetter—between 3 and 5 percent of thearea was not burned. By far, the fall-grazed pastures fared best, with between

BiodiversityBiodiversityRebounds AfterRebounds AfterWildfireWildfire

Up From the Ashes

Right: Steven Seefeldt, rangelandRight: Steven Seefeldt, rangelandscientist, checks the depth of springscientist, checks the depth of springwheat seeds planted by a rangelandwheat seeds planted by a rangelanddrill in the fall after a fire. Fall-drill in the fall after a fire. Fall-germinating spring wheat will usegerminating spring wheat will useexcess soil nutrients, compete withexcess soil nutrients, compete withexotic weeds in the fall, and die inexotic weeds in the fall, and die inthe winter, providing improvedthe winter, providing improvedground for spring planting ofground for spring planting ofnative plant species.native plant species.

Far right, top: Herding sheep toFar right, top: Herding sheep toresearch sites at the U.S. Sheepresearch sites at the U.S. SheepExperiment Station near Dubois,Experiment Station near Dubois,Idaho. These sheep, with theirIdaho. These sheep, with theirdiverse diet preferences, may helpdiverse diet preferences, may helpnative species compete againstnative species compete againstinvasive species in the sagebrushinvasive species in the sagebrushsteppe.steppe.

Far right, bottom: Steven SeefeldtFar right, bottom: Steven Seefeldtand Scott McCoy, range scienceand Scott McCoy, range sciencetechnician, collect soil after a fire totechnician, collect soil after a fire todetermine nitrogen levels.determine nitrogen levels.

A prescribed fire at the HenningerRanch of the U.S. SheepExperiment Station near Kilgore,Idaho, is used as part of a researchproject to determine how toestablish native vegetation afterfire in the sagebrush steppe.

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21Agricultural Research/March 2003

15 and 20 percent of the area remainingunburned.

Species: Variety vs. AbundanceSince the fire, Seefeldt and USSES

technician Scott McCoy have been re-cording the types of vegetation that aregrowing back in the different pastures.

“The number of species each pasturesupports now is virtually identical,” saysSeefeldt. The formerly fall-grazed andungrazed pastures currently support 70species each, and the formerly spring-grazed pastures support 69.

The differences become noticeablewhen the relative abundance of each ofthe species the pastures support is takeninto consideration. Seefeldt and McCoysay that more of the spring-grazed landis now taken up by invasive and annualspecies.

This research will add important in-formation to the debate about the conse-quences of grazing—and its timing—onbiodiversity.

To Graze or Not To Graze . . .In a related study, Seefeldt is looking

at the effect sheep have on rangelandwhen they’re allowed to graze relativelysoon after a wildfire.

Seefeldt explains that in the pastdecade, hundreds of thousands of hec-tares of rangeland in the western UnitedStates have burned in wildfires. To allowthese areas time to recover, land mana-gers usually prohibit livestock fromgrazing on them for 2 to 3 years. Un-fortunately, in many cases, the land istaken over by exotic invasive weeds be-fore livestock are reintroduced. Theinvasive weeds can crowd out nativevegetation, change fire frequency, de-crease palatable forage for native ani-mals, and increase soil erosion.

The research currently available re-garding when to begin grazing again onburned areas does not take into accountgrowth and development of invasiveweeds and their effects on native plants.To address this lack of data, Seefeldt has

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teamed with Karen Launch-baugh, a professor of range-land ecology at the Universityof Idaho.

Woolly Weed WhackersSheep are efficient fora-

gers and, unlike cattle, canthrive on a fair number of in-vasive weeds, such as leafyspurge and spotted knapweed.After the fire of 2000, See-feldt says the experimentstation had a great opportun-ity to determine which plantswould take root most quicklyafter a fire and to find out howgrazing animals such as sheepwould affect the rangeland’srecovery.

He hypothesized that ifsheep were allowed to grazerelatively soon after a fire, ahigher percentage of invasiveplants would be eaten, givingnative vegetation the time itneeded to reestablish itself.

If Seefeldt’s hypothesisturns out to be correct, sheepproducers could benefit justas much as native plant spe-cies. They could offer theiranimals’ services as range-land rehabilitators after a fire.

The idea of using sheep asbiological control agents forweeds has precedent. In Can-ada, some producers are paidas much as $5 per sheep permonth to have their animalsgraze on lands that are part ofreforestation projects. Boththe producers and the landmanagers benefit in this situ-ation. The sheep get paid toeat, and the land managersspend much less money thanthey would have on herbi-cides or mowing. Also, sheepcan be herded to wherethey’re needed most—unlike

insect biocontrol agents.When the season’s over, theirwool, meat, and lanolin canbe sold for profit.

To test whether sheep willkeep invasive plant popula-tions in check on burnedrangelands, Seefeldt hasfenced off spring-graze, fall-graze, and control—or no-graze—pastures in the burnedarea. Because of an atypicalweather pattern in southernIdaho during the winter of2001-2002, growth of inva-sive downy brome was sup-pressed on all pastures duringthe first year of the study.

The team has evidence thatletting sheep graze on recov-ering rangeland is not neces-sarily harmful—if the grazingis managed correctly. See-feldt describes the lack of afence-line contrast betweentwo pastures in the study.“The pastures looked nearlyidentical in the summer of2002, even though one hadbeen grazed in the fall of2001 and the other hadn’tbeen grazed at all since thefire,” he says.

Seefeldt and his collabora-tors will continue the studyfor 2 more years.—By AmySpillman, ARS.

This research is part ofRangeland, Pastures, andForages, an ARS NationalProgram (#205) described onthe World Wide Web at www.nps.ars.usda.gov.

Steven S. Seefeldt is withthe U.S. Sheep ExperimentStation, HC 62, Box 2010,Dubois, ID 83423; phone(208) 374-5306, ext. 112, fax(208) 374-5582, e-mailsseefe ld t@pw.ars .usda.gov. ★

Steven Seefeldt and Scott McCoy record the types of vegetationthat have grown back in a pasture since the fire occurred.

After a prescribed fire at the Henninger Ranch of the U.S. SheepExperiment Station near Kilgore, Idaho, experiments will beconducted to determine how to establish native vegetation in thesagebrush steppe.

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