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Beware Alien Invaders

The Nature Conservancy Urges Wyoming Gardeners to Help Stop the Spread of America’s Worst Weeds

Lander, WY—March 20, 2004—On the first day of spring, The Nature Conservancy is asking Wyoming residents to check their yards and gardens for plants that can escape cultivation and cause tremendous damage to the natural environment and the local economy.

Trees such as Russian olive and saltcedar and plants such as oxeye daisy, purple loosestrife, common tansy and yellow toadflax (also known as butter-and-eggs) have been used widely in horticulture and landscaping, and can be found in backyards and business lots across the region. At first glance these plants may look pretty, but their beauty is deceptive.

Known as invasive species, plants like these are typically transplants from distant places.  Once free from the natural checks and balances in their native habitats, these alien invaders establish themselves in new areas and quickly spread out of control. They hoard light, water and nutrients, and can alter entire ecosystems by changing soil chemistry.

With intentional and unintentional assistance from people, these problematic plants are spreading at an alarming rate, infecting natural areas across the United States.

“Keeping invasive plants out of America’s backyards helps the environment and the economy,” said Steve McCormick, president of The Nature Conservancy. “Taking the time to remove invasive plants and replace them with non-invasive varieties is a great example of bringing new energy to the old adage: think globally, act locally.”  The Nature Conservancy is working across the country to control invasives and prevent them from destroying natural ecosystems. 

“Not only do exotics like leafy spurge have tremendous negative impacts on Wyoming economically, these non-native species are one of the single greatest threats to biodiversity in our state,” said Dr. Joni Ward, Director of Science for the Wyoming Chapter of the Conservancy.  “Fortunately, one of the foremost authorities on invasive species in the entire country is Fremont County’s Weed and Pest Control Department, so help is here for those who seek it.”  Ward notes that there are similar departments in all Wyoming counties.

According to Lars Baker of Fremont County Weed & Pest Control Department (Weed and Pest), “The Wind River drainage is one of the most impacted in the state by an invasive known as Russian knapweed.  This species thrives primarily in irrigated pasture areas, crowding out more favorable grasses that wildlife and cattle depend on.”  Cattle can eat Russian knapweed, but it tastes bitter so typically avoid it.  Horses may sicken and die if they eat it.  Because it is a deep-rooted perennial, treating Russian knapweed over a period of time is required in order to allow enough time for native vegetation to become competitive and overcome the weed.

In 2002, Weed and Pest implemented a three-year research project on The Nature Conservancy’s Winchester Ranch, which is in the Dubois-Crowheart Weed Management Area.  In addition to Russian knapweed, perennial pepperweed is also found on the Winchester, as it is on most ranches in the Wind River watershed.  Perennial pepperwood is an invasive weed that also occurs in riparian (along streams) pasture but even more readily invades pristine areas, effecting native plants and wildlife.  The Department has designated plots for testing four different herbicides on these species with the goal of finding the most effective treatment with the least effect on non-target species.  This information will help the Conservancy treat weed problems with minimum impact on native plants and wildlife, and the most effective practices will be passed on to other landowners.

Preliminary findings of the Winchester Ranch studies indicate that lower rates of herbicide with multiple treatments best minimizes impact on native species.  The best time to treat is in the fall when grasses are dormant, thus minimizing damage to important forage.

Also a problem in Wyoming, particularly in the northwestern part of the state, is spotted knapweed, which invades drier areas and thus poses a threat to native wildlife such as elk. According to Baker, if the spotted knapweed problem goes unchecked, the elk carrying capacity of that area could be reduced by 50% over the next 20 years.  “Automobile springs are the perfect vehicle for transporting seed heads—that’s why we see it primarily along highways and where it has been carried into trailheads such as Double Cabins.”

Saltcedar, or tamarisk, is an emerging threat in Wyoming both to biodiversity and the economy.  A large bush or small tree that grows along streams and rivers, saltcedar can soak up 200 gallons of water per day!  It also accumulates salt in its tissues, redistributing it to shallower soil levels, making it unsuitable for many native species.  This aggressive invader can replace cottonwoods, willows and other native vegetation due to its ability to access the water table at a greater depth.

Because many invasive plants are spread by unsuspecting gardeners, The Nature Conservancy has created a wallet insert that gardeners can carry with them when shopping at their local nurseries. The insert lists the worst invasive plants for each region of the country. If you see one of these plants at your local nursery, do not buy it, and talk to the nursery owner about discontinuing its sale. You can find the insert in the summer 2004 edition of the Conservancy’s magazine. 

The threat posed by invasive species—both plant and animal—to the survival of native species is exceeded only by the threat of habitat loss. The cost to the national economy is estimated as high as $137 billion per year, due primarily to losses in agriculture, forestry and fisheries, as well as the cost of clearing invasive-clogged waterways and fighting invasive-fueled fires.