martes, 31 de julio de 2012

Out West, ‘Black Fingers of Death’ Offer Hope Against an Invader

Michael Friberg for The New York Times
MISSION Susan Meyer, an ecologist, in a field of cheatgrass in Skull Valley, Utah.

SKULL VALLEY, Utah — The black spears, no longer than a baby’s eyelashes, protruded in a row from the seeds that nodded on the end of the grass stalk. Susan Meyer held the cheatgrass stem with one hand and pointed them out with the other.


Michael Friberg for The New York Times

EXPANSION A dirt road runs through a field of cheatgrass in Skull Valley, Utah.

“These little marching armies of toothpicks here,” Dr. Meyer said, “that’s it. That’s the black fingers of death.” Her work these days is centered on figuring out how this fungus, which looks like a miniature mohawk haircut, does its lethal work on cheatgrass, perhaps the most disruptive invasive plant in the country — and how to help the tiny spears do more of it.

Black fingers, the fungus with the horror-movie handle, is the new artillery that wildland biologists are firing at cheatgrass, a weed that has remade the landscape of the Intermountain West. It has eliminated large concentrations of sagebrush and other native shrubs and perennial grasses by always being first.

It germinates first, uses available moisture first, burns first and, finally, is the first to reappear in damaged landscapes.

“Cheatgrass is a very insidious kind of biotic virus,” saidStephen Pyne, a Western fire historian at Arizona State University. “It takes over and rewrites the operating system. Because it grows earlier, it can burn earlier,” then in its regrowth “drive off all the other competitors. That makes for a complete overthrow of the system.”

Mike Styler, head of the Utah Department of Natural Resources, said simply: “It’s changed the entire ecology of the West.”

But the black fingers of death — Pyrenophora semeniperda — may help restoration ecologists like Dr. Meyer reclaim some beachheads in the vast swath of land already conquered by cheatgrass.

How much territory has become home to only a monoculture of cheatgrass, or is at least dominated by it? Estimates have been as high as 60 million acres, though most scientists now put the total at perhaps one-third of that. What is of greater concern is how much it could spread, and how fire cycles have changed since cheatgrass made its way here from Europe, probably carried in bags of wheat seeds. No one is certain when it arrived, but farmers were complaining about it more than 100 years ago.

An unpublished paper by Jennifer K. Balch, of the Penn State geography department, shows that fires occurred four times as often in cheatgrass landscapes in the West as in all other types of ground cover combined. The paper, which has been accepted by the journal Global Change, says that cheatgrass was a factor in nearly 25 percent of the 50 largest Western fires in the 1990s.

For decades, scientists have been trying to stop its advance, to little effect. Now Dr. Meyer and a few other scientists are exploring biological warfare. The new weapons, all fungi, are being tested here in Skull Valley, a place so thick with cheatgrass that a stubbly, bleached-blond carpet of it stretches to the hills on all sides.

The experiments depend on a fine-grained knowledge of the weed’s behavior. James McIver, of Oregon State University, who heads an interagency federal research effort on restoring sagebrush ecosystems, explained that cheatgrass — so called by farmers whose wheat yields dropped when it gained a foothold — “gets into interstices in the sagebrush plant, grows right under the sagebrush.”

Cattle, Dr. McIver said, prefer native perennial grasses, eating them when possible and leaving cheatgrass alone. In addition, said Rory Reynolds of Utah’s natural resources department, the plant’s natural rhythms give it an advantage in arid regions. Its seeds germinate in the fall instead of spring, and it begins to grow as the snows melt, getting to the precious moisture long before native plants and shrubs.

This is a crucial advantage in the high desert areas of Idaho, Nevada, Oregon, Utah and Washington, where native plants depend on scarce water resources later in the spring. It is less of a factor in moisture-rich areas to the east. Cheatgrass grows throughout the contiguous United States, but poses no threat to native vegetation outside the arid West.

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