Las Vegas Sun

March 28, 2024

Foreign invasion: Non-native grasses threaten fragile desert environment

Creosote bushes that may be 100 to 200 years old dot the soils at the Nevada Test Site, but in recent years foreign grasses have been jockeying for the same space.

The natural battle for habitat has set off an alarm among scientists.

At issue is the threat posed by the "invader" grasses taking over fragile arid ecosystems and creating fuel for fires.

The cheat, red brome and fountain grasses -- some of them used for desert landscaping -- grow quickly then dry out.

Brush fires covering hundreds or thousands of acres, such as the state has experienced in recent years, are a new phenomenon in the desert, botanist William Schlesinger, dean of Duke University's Nicholas School of Environment and Earth Sciences, said.

Schlesinger specializes in the study of arid grasses and says vegetation native to the desert would not on its own fuel wildfires as extensive as have been seen in recent years.

Creosote, which can grow for more than a thousand years, and other native plants generally do not burn extensively without added fuel, he said.

The native plants grow back slower, and as they are lost to fire, homes of birds, lizards, insects and other life surviving in the Mojave Desert for thousands of years go with them, said Schlesinger, who has studied the Mojave for more than 25 years.

"Many people would say, 'So what?' " he said. "I think the Mojave Desert is one of the most beautiful ecosystems on the planet."

If the grasses burn hot and far enough, the flames could destroy the entire landscape, leaving the desert's dust open to wind erosion and causing giant dust storms.

"The possibilities are worthy of alarm," Schlesinger said.

Schlesinger's alarm is shared by scientists at UNLV and the Desert Research Institute, who are studying the Mojave Desert.

UNLV biology professor Stan Smith is studying the effect of increasing carbon dioxide levels on undisturbed plots of desert at the Nevada Test Site, 65 miles northwest of Las Vegas. The research is intended to mimic global warming expected between 2050 and 2070.

Smith's work has shown that while both native and non-native plants are sensitive to small increases in atmospheric gases, the non-native grasses grew faster, threatening the native species.

The difference was particularly pronounced during periods of heavy rainfall. When the extra carbon dioxide was combined with more rainfall than expected, exotic invading grasses grew far more rapidly than the natives, Smith said.

That was the case in 1998, when Southern Nevada received more rainfall than normal during a Pacific Ocean warmup called El Nino.

"We've seen dramatic results in 1998, a wet El Nino year," Lynn Fentstermaker, a scientist working with Smith, said, noting that rainfall and other natural events continue interacting with the encircled plants in the open-air experimental plots.

That same year very large Western wildfires started, Smith said. "This culprit for feeding wildfires responded very rapidly," he said.

The Test Site experiment could have far-reaching implications, Smith said, because 40 percent of the world is semi-arid, like Nevada's Great Basin, the Middle East and the Russian steppes. Wildfires could pose a major threat to all of them, he said.

Along with Smith and the Desert Research Institute, the U.S. Geological Survey is studying the desert invaders.

Matthew Brooks, a USGS research botanist who lives in Las Vegas, said the invasive grasses came to America from Eurasia more than 100 years ago, their seeds in livestock feed. They have no natural enemies and thus have no competition in U.S. deserts, he said.

The Mojave Desert was long ignored by scientists, who considered it a wasteland because of baking temperatures and with scant water, he said.

While average rainfall in Southern Nevada is about 4 inches a year, thousands of species thrive -- including 200 endemic to the Mojave, he said. Joshua trees, wildflowers, lizards, rattlesnakes, the threatened desert tortoises and kangaroo rats have adapted to the climate by developing ways to survive for a long time without water.

The grasses threaten all of this life by choking out native wildflowers, some of which bloom only after intense rains. When those flowers cannot bloom, the seeds are not spread and the species die out. As the native species are displaced, shelter and food supplies for native wildlife go with them.

Could grazing help control the threat from the grasses? No, Brooks said, because the foreign grasses with their spiked flowers are not appealing food to cattle or sheep. Besides, overgrazing could disturb the environment already under threat.

"Our deserts used to have a much larger perennial grass component, but due to overgrazing in the early part of the last century, those grasses never recovered," Brooks said.

Scientists say there is no known solution right now to the problem of invading grasses.

archive