Invasive Weed Fuels A Destructive Cycle Of Fire And Growth

Jun 3, 2016

At first glance, cheatgrass looks innocuous. A dry, golden-white grass, its seeds hang down from bent stalks – seeds with sharp barbs known to harm pets. The invasive weed isn’t just a threat to cats and dogs: Cheatgrass is taking over rangelands across the West, covering vast swathes of land in dense, dry vegetation.

Cheatgrass is dense, dry, flammable, and above all continuous.

It first arrived in the U.S. just before the turn of the 20th century. A boom in unregulated livestock grazing left many places, such as the Great Basin, with bare soil and little native vegetation. Perfect conditions for cheatgrass, which soon spread throughout North America and even into Greenland.

You could say it spread like wildfire. It’s not just a cliché. It’s a threat.

“Cheatgrass is very similar to taking toilet paper and completely carpeting an area with it,” says BLM ecologist Mike Pellant.

In other words: it’s dense, dry, flammable, and above all continuous. When a wildfire burns, wind carries it from one piece of fuel to the next - for instance, treetop to treetop. But cheatgrass is like one giant piece of fuel. The fire will move along the ground as fast as the wind does.

The Great Basin, home to much of the West’s sagebrush – and thus the endangered sage grouse – has a massive cheatgrass problem. But it’s also a serious issue in Washington. Steven Link, a scientist with the Confederated Tribes of the Umatilla Reservation, says the weed has gradually increased its presence across south-central and eastern Washington for more than a century. Overgrazing, and soil disturbance, are again the culprits.

“Anything that disturbs the soil and destroys the protective powers of the perennial bunch-grasses” can lead to more cheatgrass, Link says.

Once cheatgrass cover reaches 45 percent, ignition is almost certain.

And the relationship between the invasive weed and fire is easily quantified. Once cheatgrass cover reaches 45 percent, Link says, the chance of fire with any source of ignition is 100 percent. All it takes is a firework, a campfire or a lightning strike.

Here’s where it gets worse. When wildfire burns out an area, cheatgrass comes back first. It starts growing in February and is flammable by May. This creates what Mike Pellant describes as a ripple effect. The weed grows in an area, then burns in summer. But the fire also kills off native plants. Cheatgrass takes over where those plants once grew. The next year it happens again. More fire, more cheatgrass, more fire, and so on in an ever-widening area. It’s one of the reasons that wildfires have kept getting worse.

On top of that, Pellant says increased carbon dioxide linked to climate change has a more direct impact on the invasive weed.

“Probably the biggest concern is that cheatgrass better utilizes carbon dioxide than our native plants,” Pellant says.

Ending the cycle either means stopping cheatgrass from catching fire -  which isn’t possible - or getting rid of the cheatgrass. Fire officials dig lines to stop fire from spreading. They plant less-flammable vegetation as a fire line, known as “greenstripping.” And they reduce cheatgrass through mowing or with targeted livestock grazing. There are also herbicides used to kill off the weed.

This is the cycle of weeds and wildfire: more fire means more cheatgrass, and that fuels more fire, and so on in an ever-widening area.

The most common strategy is to re-establish native vegetation after a fire. This helps the ecosystem to recover from fire, and can make it harder for cheatgrass to return. It also staves off soil erosion, something cheatgrass doesn’t do. Among the efforts to do so: the creation of “seed pillows” to encourage more growth of native plants.

And a couple years ago, a new method emerged: bacteria. Ann Kennedy, a soil scientist with the Agricultural Research Service and an adjunct professor at Washington State University, found two strains of bacteria are even more effective than herbicides for killing cheatgrass: they attack its roots. The new method won’t solve the problem on its own – cheatgrass occupies hundreds of millions of acres, and the bacterial treatment is expensive – but it is another tool that can be used to eradicate the invasive species.

Steven Link doesn’t just see eliminating cheatgrass as a way to reduce fire risk. He says it’s part of reestablishing the natural ecosystem.

“It’s just a beautiful activity,” Link says. “And society should find that interesting.”


Copyright 2016 Northwest Public Radio