Oh noes! Giant thistle weeds a coming consequence of climate change, but another study says "maybe not"

Yellow starthistle is indeed a problem in western states, but the problem preceded “climate change” by decades.  See the end of the press release for more.

Climate change allows invasive weed to outcompete local species

WEST LAFAYETTE, Ind. – Yellow starthistle already causes millions of dollars in damage to pastures in western states each year, and as climate changes, land managers can expect the problem with that weed and others to escalate.

When exposed to increased carbon dioxide, precipitation, nitrogen and temperature – all expected results of climate change – yellow starthistle in some cases grew to six times its normal size while the other grassland species remained relatively unchanged, according to a Purdue University study published in the early online edition of the journal Ecological Applications. The plants were compared with those grown under ambient conditions.

“The rest of the grassland didn’t respond much to changes in conditions except nitrogen,” said Jeff Dukes, a Purdue associate professor of forestry and natural resources and the study’s lead author. “We’re likely to see these carbon dioxide concentrations in the second half of this century. Our results suggest that yellow starthistle will be a very happy camper in the coming decades.”

The study is one of the first comparing the growth of invasive species versus their local competitors under future climate scenarios. Dukes believes the results indicate problems land managers and crop growers could see in the coming decades, and not just with yellow starthistle.

“Plants are going to respond in a number of ways to climate change. Sometimes, the species we depend on will benefit, but other times, it will be the weedy, problematic species that benefit most, and there can be economic and ecological damages associated that people should be aware of,” Dukes said. “These problems with yellow starthistle aren’t going to go away on their own. If anything it’s going to become more of a problem than it is now.”

Yellow starthistle is a significant weed in the West, especially in California, where it has a longer growing season than native plants and depletes ground moisture, affecting water supplies.

“It reduces the quality of the area for animal forage, is toxic to horses and when it forms spines, cattle don’t want to eat it,” Dukes said. “Many consider yellow starthistle to be the worst grassland weed in the West.”

The decreased pasture production, lost water, and control costs associated with yellow starthistle cause economic impacts in many western states. Experts suggest that in Idaho alone, the weed may cause more than $12 million a year in economic damage and that yellow starthistle reduces pasture values by 6 percent to 7 percent across the state of California.

Dukes said all plants increased in size as expected when exposed to more nitrogen. But yellow starthistle was especially responsive to increased carbon dioxide.

That might be in part because the weed can gain access to more soil resources, Dukes said. Grassland plants’ stomata, small porelike openings on the leaves, don’t have to be open as wide to take in carbon dioxide when there is a larger concentration in the air. Those smaller stomata allow less water to escape, and the extra water in the soil could favor yellow starthistle. The added carbon dioxide also changed the mix of species competing with the weed and may have allowed it to grow a more effective root system.

“It was an impressive increase in growth,” Dukes said. “It was one of the largest responses to elevated carbon dioxide ever observed.”

Biological control species introduced to control yellow starthistle have not been effective enough, and Dukes said it is becoming urgent that better controls be developed to address invasive species that could cause significant damage to pasture, cropland and wildlands.

The National Science Foundation and the David and Lucile Packard Foundation funded the research, which was carried out in collaboration with researchers at the University of Massachusetts Boston, Stanford University and the Carnegie Institution for Science.

Writer: Brian Wallheimer, 765-496-2050, bwallhei@purdue.edu

Source: Jeff Dukes, 765-496-1446, jsdukes@purdue.edu

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From Wikipedia: it seems the spread of this weed preceded the global warming issue by decades:

After the turn of the 20th century, Spain, France, Italy, and perhaps Turkestan were also likely sources of the invasion’s seed. Since its introduction to California in the mid-nineteenth century, it has become a large-scale invasive species (noxious weed or invasive exotic) throughout twenty three states. It currently dominates over 15,000,000 acres (61,000 km2) in California alone.

By 1970, yellow star-thistle had reached 23 U.S. states. According to the USDA Forest Service, as of 2006 the plant has been reported present in 41 of the 48 contiguous U.S. states, with the only exceptions being Maine, Vermont, and five of the Deep South states (Arkansas, Louisiana, Mississippi, Alabama, and Georgia). The plant is considered an invasive species in six of the 41 states: California, Oregon, Washington, Idaho, Utah, and New Jersey.

Also, here’s an article from 2004, by a US Forest Service expert on Yellow Starthistle, called Explosion in Slow Motion. Not a peep about climate change or global warming being a contributing factor.

Oh but wait, there’s more, just two years ago we read that climate change may actually get rid of star thistle and other noxious weeds.

From The Nature Files: An upside to climate change?

They’re the five “dirty words” of the West — cheatgrass; spotted knapweed; yellow starthistle; tamarisk; and leafy spurge — but the battle against these pervasive troublemakers could receive a boost from an unlikely ally, climate change. Scientists from Princeton University have determined that climate change will very likely cause massive die-offs of these invasive plants across the West, creating unprecedented opportunities to restore millions of acres of infected wilderness to native vegetation.

The findings, released this month in the journal Global Change Biology, will help land managers develop long-term invasive plant recovery projects. The restorative potential comes at a price however, as the model used in the study also predicts that some populations of invasive plants may simply shift their ranges to new areas — yellow starthistle will likely move from its current range in California, Oregon and Washington to a new ranges in California and Nevada for example.

Here’s the press release and link to paper:

Public release date: 27-Jan-2009

Climate change’s impact on invasive plants in Western US may create restoration opportunities

Princeton, NJ – January 27, 2009 – A new study by researchers at Princeton University’s Woodrow Wilson School of Public and International Affairs has found that global climate change may lead to the retreat of some invasive plant species in the western United States, which could create unprecedented ecological restoration opportunities across millions of acres throughout America. At the same time, global warming may enable other invasive plants to spread more widely.

The study, “Climate change and plant invasions: restoration opportunities ahead?”, was co-authored by Bethany Bradley, a biogeographer, Michael Oppenheimer, a geoscientist, and David Wilcove, a conservation biologist, at Princeton’s Woodrow Wilson School, and is published in the journal Global Change Biology.

The article is accessible online at http://www3.interscience.wiley.com/journal/121521769/abstract.

The researchers assessed the relationship between climate change and the distribution of five prominent invasive plants in the western United States – known colloquially as the “kudzus of the West” – cheatgrass; spotted knapweed; yellow starthistle; tamarisk; and leafy spurge. Such plants are defined as invasive because they were brought into this country from other lands and now dominate and alter ecosystems in ways that threaten native wildlife, agriculture, and ranching. All have greatly expanded their ranges in recent decades in the western U.S., causing millions of dollars in damage to farmlands and rangelands. Invasive plants are increasingly expensive to control, and it is widely believed that global warming will make the problem worse.

But Bradley and her co-authors find that global warming may also reduce the competitiveness of some invasive plants if conditions become climatically unsuitable to the weeds, “creating opportunities for restoration in areas currently dominated by intractable invasive species,” according to the study.

full PR article here

So we have dueling model outputs. It might be better to simply say “we don’t know”. Pass the Roundup.