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Getting the jump on grass fires.

A warm breeze wafts the pungent smell of sagebrush across a desert range. Huge, high thunderheads roll across the sky, casting shadows over land covered with dry, strawlike cheatgrass. It's a pictureperfect setting for a natural disaster--a dry lightning storm.

A phenomenon common to arid, western states, dry lightning is accompanied by a light sprinkling of rain--or no rain at all--rather than a drenching rainstorm. These peculiar storms spark wildfires in desert rangelands, particularly in Nevada, Idaho, Oregon, and northeastern California.

True, people cause most wildfires. [See chart on page 22.] A carelessly flung cigarette butt or hot automobile exhaust will quickly ignite dry grasses near a highway. But lightning can set many fires simultaneously over large landscapes, increasing the chances for a serious wildfire.

"Wildfires can destroy thousands of acres within a matter of hours," says James A. Young, a range scientist at the ARS Conservation Biology of Rangelands Unit in Reno, Nevada. In 1985, wildfires near Winnemucca, Nevada, charred more than 600,000 acres. Firefighters blamed it on a dry lightning storm, noting that over 50 different strikes within a few hours contributed to the blaze.

These wildfires burn valuable forage grasses that feed cattle and sheep, as well as mule deer and pronghom antelope. Fires also destroy both shelter and food for wildlife such as kangaroo rats, jackrabbits, and nesting birds--sage grouse, chukars, and sparrows.

To help prevent range fires, ARS scientists are studying new ways to better establish both native and introduced grasses. And they are looking at how fires alter rangeland soils and how those changes may affect plants.

One grass that scientists would like to replace is cheatgrass, an alien weed that flourishes on most western rangelands. "It's not that cheatgrass isn't a good forage," says Young. "In fact, it's fairly nutritious until it matures--typically around mid-July. Then it becomes a dry, fine-textured straw with prickly seedheads that can hurt cattle's mouths. And it's highly flammable."

Other grasses stay green throughout the summer, when cattle graze the range. However, these native perennial species have a hard time competing with cheatgrass, an annual that reseeds itself each spring and sprouts quickly.

"One way to get around that problem," says Stuart P. Hardegree, "is to coax these perennial grasses to sprout more quickly. This may give them a critical head start so they can outgrow cheatgrass."

Hardegree, a plant physiologist at the ARS Northwest Watershed Research Center in Boise, Idaho, is perfecting a way to do just that--a technique called seed matric priming. "Matric,"a term from soil physics, refers to the amount of water available in a matrix. Soil and sponges are good examples of matrixes, which are actually conglomerates of porous material.

The method primes seeds to sprout by plumping them full of moisture without submersing them, so that the seeds actually stay dry on the surface. Matric priming is an improvement over another sprouting enhancement technique known as osmotic priming, in which seeds are soaked in a solution of polyethylene glycol (PEG), a clear, syrupy liquid. The antifreeze used in cars contains a form of the same chemical.

"The main problem is that PEG is a goopy mess, so you have to wash the seeds before they're planted," says Hardegree.

Matric priming, or matric conditioning, as it is also called, avoids that problem. "The seeds never touch the PEG, because they're separated by a thin membrane made of cellulose," he says.

In the laboratory, a pill-bottle-sized germination priming vial holds the solution. Inside is a smaller vial, holding seeds sitting on the membrane.

The membrane's pores keep out the PEG but allow water to seep in, which the seeds in turn soak up. The key is creating the perfect mixture with just enough water for the seeds to begin to metabolize, but not so much that they extend a root, explains Hardegree.

He then compares the germination time of primed versus unprimed seeds, at both 10[Degrees]C and 25[Degrees]C (50[Degrees]F and 77[Degrees]F). "We find we can cut germination time almost in half with three different grass species," says Hardegree.

At 10[Degrees]C, thickspike wheatgrass, sheep rescue, and bluebunch wheatgrass normally germinate in 7 to 9 days, but when primed they germinate in 4-- about the same as for cheatgrass.

According to Hardegree, the research may benefit a variety of user groups. "Native plant biodiversity is being emphasized more and more these days," says Hardegree. "Instead of revegetating rangelands with a single species, there's a growing trend to create richly diverse areas that include a variety of appropriate species."

With this in mind, the U.S. Department of the Interior's Bureau of Land Management has established an Intermountain Greenstripping and Rehabilitation Research Project.

Greenstripping means planting strips of green vegetation to act as fuel breaks to slow or stop wildfire spread, according to Mike Pellant, a greenstripping specialist with the BLM in Boise.

It's the rancher's version of fuel breaks that homeowners use in fireprone settings, such as southem California's notoriously flammable canyons of chaparral. There, homeowners are advised to landscape with low-growing, slow-burning greenery.

In Idaho, most greenstrips are about 300 feet wide and have been seeded along highways and railways. Researchers first plow under existing cheatgrass and use special drills to plant the seeds.

So far, the practice has worked well where the seeds took hold. "Two fires that reached greenstripped areas didn't bum through," says Pellant. For example, a greenstrip south of Grasmere, Idaho, helped stop a wildfire in 1988.

But not every planting is a success, notes Pellant. The 6-year drought in the West caused seeding failures in several instances.

Currently, the challenge is to promote better establishments and earlier sprouting, which Hardegree hopes to achieve over the next few years. Seeds with shorter germination times, he says, can take better advantage of favorable conditions--like soil moisture--that may be available only for a short time, as during a drought.

He plans to field test his primed seeds next spring on BLM land near Boise. The following year, he'll gear up for large-scale applications of the priming technique. "Once we determine the optimal amount of water needed to prime a particular batch and type of seed, then we can add just the right amount. And, when the conditions are right, we'll test to see how well the primed seeds do in reseeding a burned-over area."

When flames roar across a range, the soil reaches temperatures above 300[Degrees]C (572[Degrees]F). "After soil gets that hot, the growing environment is dramatically altered," says Robert R. Blank, a soil scientist who works with Young.

For one, burned soils are extremely hydrophobic, or very slow to absorb water. That's due to waxlike hydrocarbons-formed by burning plant materials-that coat soil particles. "A drop of water will sit like a bead on top of burned soil for 2 hours," says Blank. Normally, water soaks into most soils almost immediately.

Another difference shown in preliminary studies was the presence of acetic acid and formic acid in burned soils. (Both are quite common chemicals: Vinegar is weak acetic acid, and ants contain formic acid.) "It's possible that these compounds--or others we haven't yet detected-Could influence seed germination," he says.

One advantage though: The heat of burning splits apart a potassium-containing mineral called biotite. "The splitting increases the mineral's surface area," explains Blank. "That makes it easier for growing plants to absorb this essential nutrient."

More extensive studies after the next fire are planned for Nevada's Great Basin desert. Blank and colleagues will compare germination times of up to 20 different species of grasses, shrubs, and other plants, seeded in both burned and nonburned areas.--By Julie Corliss, ARS.

James A. Young and Robert R. Blank are with the USDA-ARS Conservation Biology of Rangelands Research Unit, 920 Valle), Rd., Reno, NV 89512. Phone (702) 784-6057, fax number (702) 784-1712. Stuart P. Hardegree is at the USDA-ARS Northwest Watershed Research Center, 800 Park Blvd. Plaza IV, Suite 105, Boise, ID 83712. Phone (208) 334-1363, fax number (208) 334-1502.
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Title Annotation:range grass research
Author:Corliss, Julie
Publication:Agricultural Research
Date:Sep 1, 1992
Words:1338
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