Scott Yates — East Oregonian Publishing Group Weeds like the Russian thistle and tumble mustard shown here, caught in the fence line along Washington Highway 2 in Eastern Washington, could become an even greater problem for farmers if climate change scenarios envisioned by some researchers come to pass.
Dan Ball
A SPECIAL REPORT: Second of three parts Along with the drier landscape comes another problem: more weeds
By Scott Yates East Oregonian Publishing Group
SPOKANE, Wash. - Bigger weeds. Weeds that go further up mountainsides. Weeds that take advantage, not only of warmer temperatures, but higher carbon dioxide levels that will accompany global climate change.
The future is weedy.
But then, so is the present.
Which is why Northwest weed scientists aren't panicking over the impact of global warming on weeds.
Besides, as Dan Ball, professor of weed science at Oregon State University's Columbia Basin Agriculture Research Center said, "Everybody is shooting from the hip when they make predictions about what's going to happen with global warming."
Ball takes his aim by suggesting that less severe winters in the Northwest will mean diminished winter kill for weed species like barnyard grass or crabgrass. And warmer temperatures will promote quicker weed growth.
"It may come to the point that if growers are relying on the calendar to make their herbicide application, they might find themselves late," he said.
Ball has been studying weeds for 25 years and although he's seen a shift in populations during that time, he doesn't necessarily attribute the differences to global warming. He said the drought cycle is responsible for the march of weeds like Russian thistle and prickly lettuce. Only if that cycle is influenced by global warming can the advance of these weeds be attributed to it.
The fact weed scientists sound fairly sanguine when it comes to the potential for weed population shifts as a result of global climate change may be because change is the name of the game in their profession. Not only has the globe's interconnected commerce presented opportunities for expansion of weed species, so have growers' changing farming practices. Not to mention changes brought about as a result of chemical resistance in weeds.
Tim Prather, a weed ecologist in the Plants, Soils and Entomological Sciences Department at the University of Idaho, said one of the most important contributors to any weed problem is human activity. Regardless of what global warming does, the United States will continue to see introduction of new species "unless we can improve our system for keeping them out."
As for the weeds and other native plants that are already here, Prather said the weather will either expand or contract their range. An already notorious weed, cheatgrass, could become an even bigger threat in the sagebrush and grasslands of the Western Great Basin.
Research indicates that global warming and enhanced CO2 will lead to bigger cheatgrass plants. The weed is also known as downy brome. Additionally, scientists believe the weed's palatability will decline, leaving more of it on the surface to serve as fuel for fire.
An indication that might already be happening is the fact fire return intervals - cycles of time over which catastrophic fires can be expected - have decreased dramatically. Prather said it used to be 60 or even 120 years would pass between fires. Lately the interval has declined to less than 10 years and, in some cases, five years.
Joe Yenish, extension weed scientist at Washington State University, said the range of weed species may also be expanding. In Washington, kudzu, a noxious invasive weed from the Southeastern United States, was recently found in Vancouver, Wash.
"It seems to be creeping up the West Coast, acclimating as it goes along," he said.
But Yenish believes the greater danger of climate change to the regional weed ecology is the potential for weeds to survive at higher elevations and even migrate from one side of the Cascades to the other. For instance, milder winters in the eastern part of the region could allow a west-side weed like scotch broom to become established.
Yenish said the bigger factor in the spread of weeds may not be temperature, but rather precipitation shifts. Drier conditions, he said, would allow a weed like Russian thistle to advance further eastward "because a drier environment gives it a competitive advantage."
Scott Yates is a Capital Press staff writer based in Spokane, Wash.
