In Ranchers Vs. Weeds, Climate Change Gives Weeds An Edge

Most climate models paint a bleak picture of the Great Plains a century from now as a hot region besieged by heavy rainstorms and flooding.

And new studies suggest that climate change may bring farmers another headache: more invasive plants.

Ask most Midwestern and Rocky Mountain ranchers about the weeds they pull their hair out over and be prepared for a long list. There's cheat grass in Nebraska, red brome in Utah and yellow star thistle in California.

And they can't count on cattle to gobble them up. Depending on the plant, most cattle either don't want to eat it or could get sick if they do.

"You kinda have to teach them about a new plant," says Ellen Nelson, a rancher in north-central Colorado who has a weed problem. "I've gotten some of them to eat some, but in general, that's a hard one."

As climate change takes hold, it's likely to only get worse, not just for Nelson, but for ranchers across the country. In 2005, U.S. Department of Agriculture research ecologist Dana Blumenthal set out to find out just how it will get worse. Specifically, he wanted to know what effect climate change will have on a noxious weed called Dalmatian toadflax that's encroached on grasslands in 32 U.S. states.

For about eight years Blumenthal and his team simulated one possible future climate in the Wyoming grassland. They used a heating apparatus to keep test plots warmer than normal, and 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.

"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.

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.

Back at Ellen Nelson's ranch, she's formulating this year's plan of attack against the toadflax. She's welcoming a new class of steers. Their first lesson will be to learn to love the taste of toadflax.

"Maybe we're going to learn how to live with some of these weeds," she says. "That might be heretical to say."

But it's a heresy that many of her fellow ranchers will have to get used to keep producing beef for American tables.

Luke Runyon reports from Colorado for KUNC and Harvest Public Media, a public radio reporting collaboration that focuses on agriculture and food production issues. A version of this story originally appeared on Harvest Public Media's site.

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