Passage IV

NATURAL SCIENCE: This passage is adapted from the article “Prairie Islands” by Sam Hooper Samuels (@2005 by the Sierra Club).

It’s a fine day for a prairie fire. Wind is steady at 10 to 15 miles per hour from the southeast, and the humidity hovers around 50 percent. For early August in Iowa the weather is cool and won’t overheat the crew. Kevin Pape, a ranger for Stone State Park, attired in a flame-resistant suit and broad-brimmed fire hat, exudes quiet confidence as he passes among the workers. He’s handing out aerial photographs marked with letters and boundary lines of the next unit to be burned.

Pape and his crew are preserving prairie in the Loess Hills of Iowa by torching it.

These are some of Iowa’s last and most ecologically diverse prairies, and they’re disappearing like drops of water on a hot skillet. Of the vast prairie that once blanketed the Hawkeye State, less than one-tenth of one percent survives. Of that tiny remnant, more than half is here in the Loess Hills, a long band of steep peaks, some jutting up to 400 feet, hugging the Missouri River valley along the western edge of the state. The hills are Iowa’s secret treasure, a 650,000-acre miniature mountain range that punctuates the famous flatness of the Midwest with sharp slopes and cool, sheltering hollows.

The hills were blown in, particle by particle, on the winds. The Loess Hills get their name from the dirt they’re made of. It’s a German word, Loss. It rhymes with “fuss” and means dust, literally “loose.” Loess is fine yellowish mineral stuff, rock pulverized by glaciers over the 150 millennia of the last ice age and carried south by rivers. When the rivers dried, they left tons of this siltlike powder to be picked up by winds and scattered across the heartland.

Under the rich topsoil of its green croplands, most of Iowa is covered in a 50-foot-deep blanket of loess. Only here, though, where the winds from the west met the Missouri’s eastern shore, was the loess dumped in great heaps. The only other landform like it is along the banks of China’s Yellow River, named for its loess-clouded waters.

Fragile Giants is what scientific historian Cornelia Mutel titled her 1989 book, the best natural history yet of the hills. Fragile indeed. Where the loess is exposed, you can break it off in chunks and crumble it to a powder that disappears almost before it hits the ground.

From the ground, the topography calls to mind the intricate, pleated patterns of sand dunes. Long, meandering ridges are like spines with rows of smaller ridges projecting out like ribs, and even smaller spur ridges projecting from these in turn. Natural terraces follow the hills’ contours because of the mineral soil’s peculiar inclination to compact into straight vertical walls. These “catsteps”—unmistakable signatures of loess terrain—create a complex network of ridges, a hiker’s dream of hilltop mazes with nonstop prairie vistas.

Most of Iowa’s prairie long ago fell victim to the plow or the pavement. But because the Loess Hills are often too steep for row crops, pockets of high-quality virgin prairie remain. Big bluestem, little bluestem, sideoats grama, prairie clovers, lead plant, and dozens of other grasses, sedges, and flowering plants mottle the hills.

When Lewis and Clark passed within a few miles of this spot 200 years ago, it was largely a treeless landscape. Back then, fire would scorch any given patch of prairie every four to seven years. In autumn, the dry plants could fuel towering flames and intense heat. These conflagrations could advance faster than a person on horseback could flee, but they were as vital to the survival of a prairie as water itself. Prairie plants evolved root systems up to 15 feet deep to survive the flames.

To bring fire back, Pape and his crew are part of a network of prescribed-burn fire-setters called the Stewardship Committee. Of the hills’ 650,000 acres, only about 18,000—a patchwork of state, county, and privately owned parklands—are under any sort of conservation management. The committee does its best to burn those areas as regularly as nature once did. It’s a sort of latter-day ecological posse, a band of professionals trained in fire management that convenes whenever and wherever conditions are right to incinerate bad guys like overgrown sumac, dogwood, eastern red cedar, and the invasive Siberian elm.

It takes less than an hour for the committee to transform the patch of lush prairie into a smoking black blanket. All around, the scorched skeletons of hundreds of young sumac trees stand, still vertical but ready to disintegrate into ashes. In a few weeks, this area will be green again.