Amber Waves of Weeds II: Invaders Threaten to Destroy South Dakota Economy: Who Cares?

Tuesday, 28 July 2009 09:20

 

Written by Sam Hurst

 

South Dakota cowboy riding his fence line in the heat of a summer afternoon could be forgiven for thinking that the slender woman with the broad-brimmed hat, kneeling in a patch of yellow sweet clover, was lost in the weeds. The problem is...Grace Kostel knows exactly where she is.

 

 

Kostel is a botanist (a plant taxonomist), and manager of the Black Hills State University Herbarium. She knows the grassland ecosystem of western South Dakota more intimately than any rancher, and she's walked across most of it. In 2004 and 2005 she conducted a formal floristic survey of both the Oglala National Grasslands and the Buffalo Gap National Grasslands. Every summer, eyes to the ground, she keeps discovering new and expanding weeds at a rate that should terrify every rancher on the northern plains.

 

How does Kostel find a new weed? How does she look past the dynamic diversity of the grasslands to see something new? "Do you go around looking for a strange plant?" I asked her. "How do you know what to look for?" "I have spent so much time walking grasslands..." she answers, "...I know when things don't look right."

 

Near the entrance to Badlands National Park, north of I-90, Kostel spent a recent morning with a team of ecologists from the Park and Buffalo Gap National Grasslands exploring a public pasture for sulfur cinquefoil (Potentilla recta). Forest Service rangers spotted suspect plants early last summer, and shipped them off to Kostel who confirmed that a new weed had invaded the neighborhood.

 

The pasture has been heavily grazed since scientists last visited, so everything looks different when the group arrives. Then Shelly Gerhart from the Forest Service spots it...a single plant here, then there. Everybody begins to point toward the ground. "There's one. Oh, there's another one." Milt Haar, a grassland ecologist with the Park Service comments that sulfur cinquefoil looks very similar to a native cinquefoil. I squint. I'm embarrassed to admit that all I see are green plants. But everyone else is looking down, savoring the details, the complexity, the subtle differences plant to plant. Within minutes the circle has expanded twenty feet. And that is the heart of the problem.

Spray teams that fight an invasion of exotic weeds explore outward from the plants they discover, determine where the perimeter is, and then spray in toward the epicenter. The strategy assumes that they can find the outside perimeter, and that they have the resources for a complete ground assault. But on the windy Plains nothing stays the same for long. Weed seeds blow and tumble. They amble across the land hidden in the hides, hooves and stomachs of cattle and small mammals. They hide in the wheel-wells of pickup trucks, and the tread of ATV tires.

 

The perimeter is always shifting, always expanding. The Forest Service never has enough resources to get ahead of the wind, or the last hay delivery from Montana or Wyoming. "We have three seasonal workers, a staff technician who uses about half his time on weed control, and one local commercial applicator trying to establish and then treat this perimeter" says Terri Harris, a range management specialist with the Forest Service. Harris coordinates the war on weeds at the Wall Ranger District. "How many people do you need?" I ask. "In an ideal world, we could keep ten people busy just inventorying the weeds."

 

Finding the battlefield is only part of the problem. The most effective herbicides used by the Forest Service--Tordon and 2,4,D--kill the sulfur cinquefoil, but threaten native forbs. Intensive grazing is a control strategy, but there is a fine line between intensive grazing and over-grazing. Fire is also a control strategy. But nothing is perfect. Once a new weed is well established, it's almost impossible to eradicate.

 

The unspoken dilemma facing these public lands ecologists is the strained relationship between federal agencies and private landowners. Ecosystems and natural forces rarely respect property boundaries. In fact, fence lines are often incubators for the spread of weeds. The Forest Service can spray public land, but if private landowners don't participate it's a losing battle. The perimeter keeps shifting...outward until the weed is just a permanent fact of life. Yellow sweet clover is a good example of a weed that is so pandemic that no local or regional containment strategy works.

 

Some of the Grassland's private permit holders are tremendous stewards of the land. Some have used their own equipment and resources to spray invasive weeds. But most ranchers don't have the money, or time, or expertise, to wage a war against weeds on the scale that scientists believe is necessary.

 

One of the ecologists shares a story with the group:

 

The Forest Service tells a rancher that they want to reduce the stocking rate in a pasture to allow native plants to recover. Sure enough, after a few years native grasses begin to re-colonize and expand, including a stand of Big bluestem, one of the crown princes of native short grass prairie. Ranchers call it an "ice cream" grass because the cattle love it.  But having never seen big bluestem before, the conscientious rancher comes into the Forest Service office and offers to spray the new weed.

 

The group groans and laughs at the story.

 

Sulfur cinquefoil is very competitive. Researchers describe its growth rate as "exponential" and cattle hate it. They will lick the dirt before they will eat it. After a few years in a pasture sulfur cinquefoil creates a monoculture, beats native plants to early spring moisture, and takes over while the biodiversity and nutritional productivity of the pasture collapses.

 

Researchers at the University of Montana have study sites where as much as 60% of the productivity of a pasture is lost when cinquefoil becomes entrenched as a competitor with native plants. In the presence of sulfur cinquefoil a ranch with a carrying capacity of a hundred cow-calf pairs collapses to forty pairs almost overnight.

 

Fifteen miles south and west, the Forest Service van pulls to a stop near a web of gentle grassy hills and ravines that drain into a meandering cedar and cottonwood draw. The group walks only a few yards when Kostel stops, like she has stepped on a rattlesnake, and blurts out, "Oh, this isn't right." They are in a thicket of sickleweed, a member of the carrot family. It is an aggressive, invasive, Eurasian tumbleweed that is spreading from the national grasslands to private ranches toward the Park and back again. It was first discovered on the Ft. Pierre National Grasslands in 2002, but Kostel found it on the Buffalo Gap near Wall last summer. No one knows exactly where it came from (most likely Central Asia to Wyoming to South Dakota). When did it arrive? How did it get here? Private ranchers who trade hay over long distances are the obvious suspects (the same is true for sulfur cinquefoil), but they are defensive and politically well-connected. They are not easy partners with the Forest Service, or with each other. Blame is almost beside the point. However it got here, the sickleweed is here now. It is spreading like a prairie fire. And each tumbling plant releases hundreds of seeds to the wind.

 

Last stop, the Conata Basin. The mid-summer heat is beginning to pound the land, and the air is so still it smothers. I feel like I have been wrapped in a hot, dry blanket and mounted on a spit. Mountain ironwort was discovered in the Oglala National Grasslands in the 1980s, and then spread under the radar for twenty years. Kostel discovered it in Conata Basin last summer. At the same time she discovered Thymalea passerina near an old homestead blowout hammered by the recent drought.

For as far as the eye can see this summer Conata Basin is covered with a blaze of yellow sweet clover, so thick that for this season, at least, it seems to have out competed the Thymalea passerina and Mountain ironwart. The revelation leads to a burst of gallows humor. "Well, we got rid of the weeds...with a massive invasion of another weed." Eyes always on the ground, Kostel stops again, "This isn't right. This shouldn't be here." She is looking down at the spider-like Halogeton glomeratus, "salt lover". It probably came from Montana. Who knows when? Like sickeweed and sulfur cinquefoil it can take over a pasture in the blink of an eye. Funny thing...a year ago no one even knew it was here.

 

The War on Weeds is under-funded, under-staffed, and most importantly, it is under-valued. Money in the farm bill to help ranchers improve conservation practices has been slashed. And yet, out of sight, weeds are re-designing the grasslands and stealing its value. Out of sight, out of mind.

 

Click here to see more photos of the invaders and the people working against them in the Buffalo Gap National Grasslands.

Written by Sam Hurst You are reading Amber Waves of Weeds II: Invaders Threaten to Destroy South Dakota Economy: Who Cares? articles