Climate change may reshuffle western weeds

Climate change will likely shuffle some of the West's most troublesome invasive weeds, adding to the burden faced by farms and ranchers in some areas and providing opportunities for native plant restoration in others, according to a new study.

In many cases, a warming climate will provide more welcoming conditions for invasive plants to get a foothold, spread quickly and crowd out native species, the study by Princeton University researchers said.

But some invasives may retreat from millions of acres in the West — at least briefly — and offer an opportunity for land managers to re-establish native plants, the study said. The window for action, though, will probably be limited.

"We're going to have to be in the right place at the right time before something else gains a foothold," said Bethany Bradley, a biogeographer at Princeton and lead author on the study.

Nonnative weeds and plants followed in the footsteps, sometimes literally, of European settlers as they spread across the West. Even one of the West's most famous symbols — the tumbling tumbleweed, also known as Russian thistle — isn't from these parts. Its origins are in Russia.

Today, nonnative plants across the West cost millions of dollars in damage to farms and ranches, alter the flow of water and function of ecosystems, provide fuels for fast-burning wildfires, and force government agencies to spend millions in response.

"Every county that I know of in the West has got nonnative or invasive weeds in it," said Steve Dewey at Utah State University's extension office. "My advice to county weed departments is to give new invaders high priority, to stop them before they get out of hand."

Bradley and two other Princeton scientists wanted to look at how changing climate conditions would effect the spread of weeds.

They used 10 atmospheric models predicting how the West's climate will change by 2100. Then they compared predicted changes in precipitation and temperature with the most hospitable conditions for five of the West's most obnoxious noxious plants: cheatgrass, spotted knapweed, yellow starthistle, tamarisk and leafy spurge.

The results were published in the latest edition of the scientific journal Global Change Biology.

Cheatgrass, for instance, will likely retreat from strongholds in southern Nevada and Utah and make further inroads into Idaho, Montana and Wyoming. The wispy grass that dominates vast stretches of the Intermountain West, might struggle in some places with warmer temperatures and less water, the study said.

Yellows starthistle may expand in California and Nevada as the climate changes while spotted knapweed moves toward higher elevations and spreads in Montana, Wyoming, Utah and Colorado, the study showed.

Leafy spurge will probably fade from portions of Colorado, Nebraska, Iowa and Oregon. Tamarisk is likely to be unchanged.

The models take into account many of the possible scenarios of a warming climate, but it's still difficult to predict changes at a local level. That's especially true for precipitation, including when it will fall and how much.

"It's a big wildcard out there," Bradley said. "Even small changes in precipitation can have big impacts on invasive and native plants in the western U.S."

And just because climate may drive out one invasive weed, it doesn't mean another won't quickly set up shop, she said. That's why it's important to find viable native plants — even those that are only native regionally, not locally — that can get established before the arrival of another invader, she said.

"The question for policy makers and land managers is, 'What do we want these lands to be?' " David Wilcove, one of the researchers on the study, said in a statement. "These lands will change, and we must decide now — before the window of opportunity closes — whether we do nothing or whether we intervene."

Models like those in the study should play a part in managing weeds in the West in the coming decades, said Dave Burch, Montana's weed coordinator and, until December, chairman of the Western Weed Coordinating Committee.

In many cases, the predictions will help weed managers know which plants to be on the lookout for and prepare for their arrival. Reacting to weed infestations gets expensive. Montana, for instance, spends $21 million a year on fighting weeds and needs to be spending $58 million just to deal of 5 percent of the weeds it already has, Burch said.

"Prevention is the cheapest way to go with weed control," Burch said. "Once you get something here, it's usually too late."