America is the home of countless species of plants introduced from the far corners of the globe over the past century or more. While many have served to beautify and enhance our lives, one particular species — Bromus tectorum, more commonly known as cheatgrass — has found itself unwelcome, crowding out native plants from coast to coast in a relatively short period of time.
Research by Boise State biology professor Steve Novak and colleagues has traced the spread of this invasive annual grass across the United States and Canada, including the year it was first noted and where it originated. Results show that the invasion was “rapid, multi-directional and genetically diverse.”
Results of the study were published in the January issue of Biological Invasions. “Invasion of Bromus tectorum into California and the American Southwest: rapid, multi-directional and genetically diverse” was authored by Angela Pawlak, a Washington State University graduate student who gathered her data in Novak’s lab. Coauthors on the paper include Novak, Jeremiah Busch and Richard Mack.
Their research looks at the plant’s range introduction and expansion in North America.
“In terms of controlling cheatgrass, we need to better understand the pathway of introduction and spread so we can try to do things that will curtail that spread,” Novak said.
B. tectorum was first noted in the United States in Pennsylvania’s Lancaster County in 1790. Genetically, it matched a variety still found in Europe. That first plant variety was joined by others as newcomers poured into the land of opportunity. As the population moved west, cheatgrass stowed away in a variety of ways ranging from wagon wheels to contaminated seed stashes.
In the late 19th century, new varieties entered the country through Western seaports like San Francisco and Seattle, and dispersed eastward. Cheatgrass was first noted in California in 1899 and varieties of the plant are now found in every state except Florida.
So what’s the big deal? It has to do with how cheatgrass grows. It germinates early in the season, well before most other plants. It spreads easily, crowding out native vegetation, such as bunchgrass and sagebrush, and the roots grow down deep, depleting moisture from the soil. It then dries up in mid-summer and becomes incredible fodder for wildfires.
Large stands of cheatgrass provide fuel for intense range fires. The problem is so pervasive that it has altered the fire cycle, leading to almost total eradication of some native plants in affected areas. Where a normal fire cycle could be every 60-100 years, scientists now are seeing cycles as tight as 3-5 years. And fingers of fire pushing through the sagebrush, allowing some plants to survive, have been replaced by a wall of fire decimating the landscape.
“If we can knock back the density of cheatgrass, we can perhaps control the intensity of the fire,” Novak said, noting that, “we still need to replace it with native species.”
Novak said that monocultures of cheatgrass often stand in areas once populated by sagebrush, bunchgrass and other native plants. Today, cheatgrass has filled in areas where livestock overgrazed and firestorms wiped the landscape clean.
Another problem with the pervasive plant is that it is palatable to livestock only in the early growing season when it’s green. Once it starts to reproduce it creates awns (bristly appendages), which can puncture the mouths (and sometimes even the stomachs) of cows.
And a single plant can produces hundreds of seeds. Add to that its ability to self-fertilize and self-pollinate and it’s easy to see how it has spread so quickly.
While Novak believes it may be too late to totally eradicate the species in North America, he does hold out hope that determining its origins can help to control it.
“If we understand its genotype and can trace it to its native range, we can discover how the plant is controlled classically,” he said. “Then we can look at the possibility of using that method to control the plant here.”
Novak currently is working on a book chapter combining the results of several studies of cheatgrass. Patterns described in the chapter are based on the analysis of 10,150 individuals from 312 North American populations of cheatgrass.