Up From the Ashes: Biodiversity Rebounds After Wildfire
A prescribed fire at the
Henninger Ranch of the U.S.
Sheep Experiment Station
near Kilgore, Idaho, is
used as part of a research
project to determine how to
establish native vegetation
after fire in the sagebrush
During the summer of 2000, a wildfire blazed through 500 hectares of grazingland at the Agricultural Research Service's U.S. Sheep Experiment Station (USSES) near Dubois, Idaho. That fire has sparked new research on the effects that grazing animals have on rangeland biodiversity and its recovery after wildfires.
Currently, there is much debate among scientists and others about how grazing affects diversity of plant species growing in grazed areas. Some say grazing is harmful; others claim it neither helps nor hurts; and still others insist it can be beneficial if managed correctly. But little data has actually been collected until now.
"When the 2000 wildfire burned through the station, it destroyed half of a long-term study," says Gregory Lewis, USSES' research leader. For more than 50 years, USSES scientists had been analyzing the effects of grazing at different times of year and the effects these grazing periods had on the plant community.
Herding sheep to research
sites at the U.S. Sheep
Experiment Station near Dubois,
Idaho. These sheep, with their
diverse diet preferences, may
help native species compete
against invasive species
in the sagebrush steppe.
During the long-term study, some pastures were grazed only in the spring, others only in the fall. The control pastures weren't grazed at all, and after 50 years, they had been taken over by a heavy canopy of sagebrush. The fall-grazed pastures had less sagebrush and more perennial forbs, while the spring-grazed pastures had less forb cover and increased grass and sagebrush.
Forbs are broadleaf plants that don't have woody stems and include perennial plants such as arrowleaf balsamroot and tapertip hawksbeard.
Rangeland scientist Steven Seefeldt says that when the 2000 fire roared through, the ungrazed pastures fared the worst. According to Seefeldt, "There wasn't a green thing left. The fire took it all to the ground."
The spring-grazed plots fared a little better—between 3 and 5 percent of the area was not burned. By far, the fall-grazed pastures fared best, with between 15 and 20 percent of the area remaining unburned.
Steven Seefeldt, rangeland scientist,
checks the depth of spring wheat
seeds planted by a rangeland
drill in the fall after a fire.
Fall-germinating spring wheat
will use excess soil nutrients,
compete with exotic weeds in
the fall, and die in the winter,
providing improved ground for
spring planting of native
Species: Variety vs. Abundance
Since the fire, Seefeldt and USSES technician Scott McCoy have been recording the types of vegetation that are growing back in the different pastures.
"The number of species each pasture supports now is virtually identical," says Seefeldt. The formerly fall-grazed and ungrazed pastures currently support 70 species each, and the formerly spring-grazed pastures support 69.
The differences become noticeable when the relative abundance of each of the species the pastures support is taken into consideration. Seefeldt and McCoy say that more of the spring-grazed land is now taken up by invasive and annual species.
This research will add important information to the debate about the consequences of grazing—and its timing—on biodiversity.
Steven Seefeldt (left),
rangeland scientist, and
Scott McCoy, range science
technician, collect soil
after a fire to determine
To Graze or Not To Graze . . .
In a related study, Seefeldt is looking at the effect sheep have on rangeland when they're allowed to graze relatively soon after a wildfire.
Seefeldt explains that in the past decade, hundreds of thousands of hectares of rangeland in the western United States have burned in wildfires. To allow these areas time to recover, land managers usually prohibit livestock from grazing on them for 2 to 3 years. Unfortunately, in many cases, the land is taken over by exotic invasive weeds before livestock are reintroduced. The invasive weeds can crowd out native vegetation, change fire frequency, decrease palatable forage for native animals, and increase soil erosion.
The research currently available regarding when to begin grazing again on burned areas does not take into account growth and development of invasive weeds and their effects on native plants. To address this lack of data, Seefeldt has teamed with Karen Launchbaugh, a professor of rangeland ecology at the University of Idaho.
After a prescribed fire at
the Henninger Ranch of the
U.S. Sheep Experiment Station
near Kilgore, Idaho, experiments
will be conducted to determine
how to establish native
vegetation in the sagebrush
Woolly Weed Whackers
Sheep are efficient foragers and, unlike cattle, can thrive on a fair number of invasive weeds, such as leafy spurge and spotted knapweed. After the fire of 2000, Seefeldt says the experiment station had a great opportunity to determine which plants would take root most quickly after a fire and to find out how grazing animals such as sheep would affect the rangeland's recovery.
He hypothesized that if sheep were allowed to graze relatively soon after a fire, a higher percentage of invasive plants would be eaten, giving native vegetation the time it needed to reestablish itself.
If Seefeldt's hypothesis turns out to be correct, sheep producers could benefit just as much as native plant species. They could offer their animals' services as rangeland rehabilitators after a fire.
The idea of using sheep as biological control agents for weeds has precedent. In Canada, some producers are paid as much as $5 per sheep per month to have their animals graze on lands that are part of reforestation projects. Both the producers and the land managers benefit in this situation. The sheep get paid to eat, and the land managers spend much less money than they would have on herbicides or mowing. Also, sheep can be herded to where they're needed most—unlike insect biocontrol agents. When the season's over, their wool, meat, and lanolin can be sold for profit.
To test whether sheep will keep invasive plant populations in check on burned rangelands, Seefeldt has fenced off spring-graze, fall-graze, and control—or no-graze—pastures in the burned area. Because of an atypical weather pattern in southern Idaho during the winter of 2001-2002, growth of invasive downy brome was suppressed on all pastures during the first year of the study.
The team has evidence that letting sheep graze on recovering rangeland is not necessarily harmful—if the grazing is managed correctly. Seefeldt describes the lack of a fence-line contrast between two pastures in the study. "The pastures looked nearly identical in the summer of 2002, even though one had been grazed in the fall of 2001 and the other hadn't been grazed at all since the fire," he says.
Seefeldt and his collaborators will continue the study for 2 more years.—By Amy Spillman, formerly with ARS.
This research is part of Rangeland, Pastures, and Forages, an ARS National Program (#205) described on the World Wide Web at www.nps.ars.usda.gov.
"Up From the Ashes: Biodiversity Rebounds After Wildfire" was published in the March 2003 issue of Agricultural Research magazine.