Invasive weeds may look forward to climate change

Mar 2, 2014

Dr. Dana Blumenthal and colleagues explain their invasive weed research during a tour of The Prairie Heating and Carbon Dioxide Enrichment (PHACE) Experiment in Wyoming.  In this test plot higher temperature and richer CO2 conditions are being simulated to study their effects on invasive weed growth.
Dr. Dana Blumenthal and colleagues explain their invasive weed research during a tour of The Prairie Heating and Carbon Dioxide Enrichment (PHACE) Experiment in Wyoming. In this test plot higher temperature and richer CO2 conditions are being simulated to study their effects on invasive weed growth.
Credit USDA: Prairie Heating and Carbon Dioxide Enrichment (PHACE) Experiment

Most climate models paint a bleak picture for the Great Plains a century from now: It will likely be warmer and the air will be richer with carbon dioxide. Though scientists don’t yet know how exactly the climate will change, new studies show it could be a boon to some invasive plant species.  

A growing problem

Ask most Midwestern and Rocky Mountain ranchers about the weeds currently causing them to pull out their hair and be prepared for a long list. It could be cheat grass in Nebraska, or red brome in Utah, or yellow starthistle in California. Depending on the plant, cattle either don’t want to eat it or could get sick if they ingest it. And getting rid of these plants is expensive.

But could climate change exacerbate an already thorny problem for ranchers? In 2005, U.S. Department of Agriculture researcher Dana Blumenthal set out to document what effect climate change will have on large swathes of grassland, focusing in on a noxious weed called Dalmatian toadflax.

A researcher with The Prairie Heating and Carbon Dioxide Enrichment (PHACE) Experiment checks a plot where climate change conditions are being simulated.
A researcher with The Prairie Heating and Carbon Dioxide Enrichment (PHACE) Experiment checks a plot where climate change conditions are being simulated.
Credit USDA: Prairie Heating and Carbon Dioxide Enrichment (PHACE) Experiment

For about eight years Blumenthal and his team simulated a possible future climate in the Wyoming grassland. A heating apparatus kept test plots warmer than normal. Pipes pumped carbon dioxide into the air surrounding the toadflax. The warming and CO2 weren’t set at doomsday levels, but rather conservative levels Blumenthal says the plains could see within a century. Under those conditions, Dalmatian toadflax flourished, growing in size 13-fold and producing more seeds. (Click here for more information on the Prairie Heating and CO2 Enrichment (PHACE) Experiment.)

“The simplest reason that invasive species are likely to do well under future conditions is that they are pretty much by definition good at dealing with change,” Blumenthal said.

A recent study suggests that Dalmation toadflax would thrive in a hotter climate that is richer in carbon dioxide, which many climate models say will exist in the Midwest.
A recent study suggests that Dalmation toadflax would thrive in a hotter climate that is richer in carbon dioxide, which many climate models say will exist in the Midwest.
Credit http://www.garfield-county.com/

That’s why Dalmatian toadflax could be emblematic of an even larger problem. Invasive species are invasive because they can adapt quickly. Similar field studies across the country have shown other nasty weeds do well in warmer, more CO2-heavy conditions. Blumenthal’s results were published in the journal New Phytologist late last year. He says there is a trend toward global climate change increasing invasion, but scientists need more data to make solid predictions.  

“There are going to be cases of invasive species, some of which we care a lot about, becoming much more problematic, and there are going to be cases of invasive species retreating from where they now exist,” Blumenthal said. “We don’t know enough to say how common this is going to be yet.”

Dalmatian toadflax is just one piece of a much larger ecological puzzle. What will America’s grasslands look like a century from now? The answer to that question affects ranchers across the Midwest, who will face expensive headaches when weeds out-compete native grasses.

Fighting a losing battle

Ellen Nelson has battled invasive plants that out-compete native grasses on her grass-fed beef ranch near Bellvue, Colo. Some climate studies suggest that fight will worsen in the coming decades.
Ellen Nelson has battled invasive plants that out-compete native grasses on her grass-fed beef ranch near Bellvue, Colo. Some climate studies suggest that fight will worsen in the coming decades.
Credit Luke Runyon/Harvest Public Media

In the summer, one hillside of Ellen Nelson’s small ranch near Bellvue, Colo., turns bright yellow. The culprit is the tall, rubbery stalks of Dalmatian toadflax. It first shot out its showy, golden flowers more than a decade ago on her property where she raises grass-fed beef. And it is a pain. It crowds out native grasses that her cattle actually like to eat.

“It’s such a tough, waxy plant that by the time it really gets going you can’t get the herbicide in it,” Nelson said.

The expensive herbicide is a relatively new weapon for Nelson. It has already cost her thousands of dollars. At first, she tried pulling the toadflax by hand, but the roots go deep and they can quickly regenerate. Then she brought in hundreds of weevils – they burrow deep and weaken the plant, failing to kill it outright. Lately, she’s been putting her faith in her steers, convincing them toadflax doesn’t taste so bad.

“You kind of have to teach them about a new plant,” Nelson said. “I’ve gotten some of them to eat some, but in general, that’s a hard one.”

Each method has only worked marginally well. Nelson admits, so far, the toadflax is winning. As time progresses, and climate change takes hold, it’s likely to only get worse, not just for Nelson, but for ranchers across the Midwest and Rocky Mountain regions.

“We are just treading water at the moment,” said Steve Ryder, coordinator of the State of Colorado’s Noxious Weed Management Program.

Like managers in most states, Ryder’s focus is on keeping new weeds from creeping in. If he has time left over from that battle, he goes after smaller populations that are quickly becoming problems, almost like stamping out spot wildfires. He’s already stretched thin and some weeds have gained a foothold.

“If climate change is going to accelerate that, then we need to decide whether to accelerate the response,” Ryder said.

Nelson and other ranchers already spend thousands of dollars battling invasive plants.
Nelson and other ranchers already spend thousands of dollars battling invasive plants.
Credit Luke Runyon/Harvest Public Media

Rancher Ellen Nelson is already formulating this year’s plan of attack against Dalmatian toadflax. It’ll likely be a mix of herbicide and burrowing bugs. The toadflax has criss-crossed her property, seeds tumbling downhill into new areas.

“Maybe we’re going to learn how to live with some of these weeds,” Nelson said. “That might be heretical to say.”

But if the climate gets more and more hospitable to noxious weeds, it’s heresy that many of her fellow ranchers will have to get used to.