This guy is lovely!" ecologist Beth Leger exclaims, falling to her knees. A tiny, energetic woman in her mid-30s, Leger hovers, bee-like, over a teensy grass with blue-green blades. It is, she tells me, a "cute" native called Poa secunda.

It's early May, and Leger, graduate student Owen Baughman and I are crouched on Peavine Mountain, a scrubby rise near the University of Nevada, Reno, where she is an associate professor of plant ecology. The ground around us is covered with the invasive annual Bromus tectorum, also known as cheatgrass. This is not surprising; the Great Basin is a disturbed landscape, and cheatgrass is now its dominant inhabitant. Around the little Poa though, there is no cheatgrass at all, just a foot of bare, pebbly dirt. "We did some trials to see what native perennials were the most competitive with cheatgrass, and it was this guy," says Leger.

Leger scoops away the soil around its base, digging carefully underneath it. "I don't want to kill him, but it's instructive to do that because his roots are super fine and they go out really shallowly, all through this area," she explains, gesturing at the bare circle. "Cheatgrass (also) has super-fine roots and this is about the only native plant I've ever seen that has the same sort of roots." That allows the Poa to take up space and use nutrients the weedy invader would typically claim. Determined to show me its root structure, Leger finally pulls the demonstration plant out of the ground, sacrificing it for the sake of knowledge. "Sorry, dude," she tells the grass. "You'll be famous."

The ancestors of Leger's beloved Poa first encountered cheatgrass, a native to parts of Europe and Asia, in the late 1800s. Western settlement had brought widespread livestock grazing to the Great Basin, a Texas-sized area that covers 180 million acres in southeastern Oregon, southern Idaho, western Utah and Nevada. That was a shock to native bunchgrasses like Poa and Indian ricegrass, which, in that part of the West, had evolved in an environment unused even to bison. Cheatgrass seized its opportunity. The weed hitchhiked from Europe in contaminated seed, straw and ship ballast, and crisscrossed the West with the railroads, which spread it with the straw used for livestock. By 1930, cheat was everywhere. As Aldo Leopold wrote in the 1949 classic A Sand County Almanac, "One simply woke up one fine spring to find the range dominated by a new weed."

That new weed would drastically change the region's fire ecology, among other things. In a typical Great Basin shrubland, forbs and grasses grow patchily underneath a canopy of well-spaced shrubs like sagebrush and shadscale. In contrast, cheatgrass masses in a smothering mane. Its survival strategy is to beat out other plants, Red Army-like, through its sheer numbers: It can drop 50,000 seeds per square meter. An annual, it dies off every year, leaving a thick thatch of flammable material. Even the smallest spark can set off fast-moving fires that kill off any remaining native shrubs. Then, next growing season, those millions of cheatgrass seeds outcompete any surviving natives. After the first burn or two, the fire cycle is forever changed. Normal fire frequency in the Great Basin is every 30-70 years; cheatgrass monocultures burn every three to 10. The bare soil left after fire can blow away in spring and land on snow in far-away mountains, causing quicker melt-off. With nowhere to hide and no shrubs to browse or nest in, wildlife -- including mule deer and the imperiled sage grouse -- quickly move out.

For many years, the Bureau of Land Management, which manages much of the land in the Great Basin, more or less ignored cheatgrass. In the mid-1980s, though, a number of large fires swept through sagebrush communities, and land managers began investigating how to protect and restore the habitat. Then, in the summer of 1999, the Great Basin burned as never before, with fires marching across almost 2 million acres. That forced the agency to take a more aggressive approach to fighting cheatgrass. Yet so far, many restoration efforts have come up short, as native soil erodes after fires, planted seeds fail to establish, and cheatgrass returns en masse. Today, ecologists estimate that it has expanded to between 20 to 50 million acres in the region, and forms a near monoculture in at least 10 to 12 million of those acres.

Cheat isn't even the worst thing that could happen to the Great Basin. Now that the ecosystem is essentially shattered, new invaders have an easier time moving in. Plants like medusahead wildrye, thistles and knapweed lurk in the wings. Unless cheat-altered landscapes can be made more resilient, one of these may become the next great invader, says Mike Pellant, a rangeland ecologist who coordinates the BLM's Great Basin Restoration Initiative. And, Pellant warns,  "we don't know which one and where and how fast. So if you think of a downward spiral, cheatgrass is not the bottom of the ecological barrel in the Great Basin."

That's the dark side, he says. "The bright side is we've got great scientists working on the problem." Of course, even the best science can't give the BLM the ability to treat 50 million acres of invaded land, especially when funding for reseeding comes primarily in a reactive rather than proactive form, tied to post-fire restoration. Pellant says any efforts to fight cheat will be mostly focused in sensitive places like wilderness study areas and important sage grouse habitat. A silver lining to the bird's decline is the federal money dedicated to keeping it off the endangered species list, which enables the agency to do more restoration.

Those priority areas can use any help that Leger, and her cheatgrass-fighting native plants, can give. And she's not alone; the effusive scientist is working alongside an Avengers-like posse of restoration scientists, all raring to put into practice new knowledge about the best way to fight Great Basin cheatgrass.