Prairies: Rediscovering a Fragile Frontier
by Howard Youth
Six-foot-tall big bluestem and Indian grass blades rustle together in the breeze, accompanied by the quick-fire yelps of calling prairie dogs. A morning on the Oklahoma prairie? Try the nation's capital. "We want to get this look throughout the exhibit," says National Zoo chief horticulturist Chuck Fillah. Fillah stands before a 8,500-square-foot living replica of American prairie, the centerpiece of the Zoo's new American Prairie exhibit.
This human-made combination of tall- and short-grass plains was a monumental undertaking that took several years to conceptualize and eight months to build. To emulate the quick-draining prairie soil and accommodate for the D.C. area's higher rainfall, construction workers dumped and spread 600 tons of carefully mixed soil and sand, installed an underground drainage system, and drilled thousands of two-inch drainage holes throughout the yard. Once the ground was ready, landscapers planted about 11,000 bare-rooted grasses and forbs, 1,500 established plants, and countless seeds. Then, six months later, Zoo horticulturist Chris Price mowed the prairie, and re-seeded it to replicate the effects of prairie fire, which makes way for fresh growth. Finally, after plants established themselves for an entire year, the exhibit's two bison set foot on the National Zoo's prairie.
Looking over the waving bluestem, Fillah says, "It's a great experiment. It will be interesting to see the bisons' impact on the plants. That is when our work will really start." Fillah adds that Washington, D.C.'s unpredictable winter weather and pervasive exotic weeds also will provide him and his crew with constant challenges. The payoff: The chance for visitors from across the National Capital area, the country, and the world to experience a bit of prairie and contemplate the fate of complex and fragile grassland ecosystems.
The National Zoo's effort to create a grassland within the District of Columbia demonstrates the complexity of preserving—and reestablishing—North America's beleaguered grasslands. Like the Zoo habitat, natural grasslands experience constant change: both naturally and at the hands of people. Before introduced cattle and associated exotic pasture weeds—before the grid of farm fields that now spans the horizons—miles and miles of waving wild grasses and forbs (herbaceous plants including wildflowers and legumes) dominated North America's interior and other areas. The fertile eastern vanguard of the grasslands—the tallgrass prairie—stretched across about 140 million acres, constituting the continent's largest connected ecosystem.
Droughts, grazing by ranging hordes of bison, fires caused by lightening, and fires set by Native Americans to drive animals, improve game's feeding habitats, or defend (their own or attack others) territory—all maintained the prairie. Today, the prairie's cycles have been tamed. In place of native bluestems and Indian grass lie pesticide-laden patchworks of corn, wheat, and other introduced grasses. Where nomadic bison once roamed, fenced-in cattle often overgraze fragile grasses and forbs and trample streamside habitats in search of water.
However, across the miles of human-made habitat, prairie remnants persist. Many are tiny, incapable of supporting bison, prairie dogs, or many other species that traditionally occurred there, but some cover thousands of acres that once again feel the touch of fire and the pounding of heavy bison hooves. In recent years, national and local efforts to revive the prairie and its wildlife have accelerated. But to create expansive ecosystems like those plowed under more than 100 years ago will be a true challenge—one conservationists hope local governments and communities will embrace.
More
than Just Waving Grass
The prairie's apparent sameness—its wide vistas and waving
grasses—deceived early European settlers. French explorers
coined the term "prairie"—meaning meadow or lawn—to
describe the vast grasslands. There was no other frame of
reference: Most Europeans in North America came from forested
areas and were unaccustomed to seeing grass stretching across
the horizon. Today, most of Americans live far from prairies
and don't understand their complexity and scarcity. We refer
to the "Great Plains" or "the Prairie States,"
when in reality these monikers reflect more our hazy elementary
school memories of history or geography lessons than the true
state of affairs. The sad truth is that very little prairie
remains--only about one percent of a biome that once covered
about 40 percent of the United States. And while prairies
are naturally low-maintenance, in our carefully controlled
world, they require lots of care.
The American prairie's vitality is linked to fire, bison, and climate. In essence, prairies thrive in what we often consider adverse conditions. Western mountain ranges shave moisture from billowing Pacific storm fronts. Legions of puffy little clouds dot the skies on the dry east side, in the rain shadow, and these meager clouds float over the plains. Water conservation is the strategy in these rain-starved regions, and prairie grasses excel there. They send their roots deep into the sod, investing up to 60 percent of their mass underground. For example, the big bluestem (Andropogon gerardii), a grass dominant in the fertile tallgrass prairie, stands up to nine feet tall, but its dense tangles of roots push almost 12 feet below ground in search of moisture. This helps grasses survive fire, which frequently occurs on the tinder-dry plains and actually fertilizes the plants. The combination of frequent wind-driven fires, extreme cold and heat, and dryness—not as dry as a desert, yet not wet enough to support forest—keeps trees at bay while grasses flourish. Grasses' deep root systems also enable them to quickly bounce back from the vigorous cropping of wandering bison.
The United States hosts different types of grassland. On the Great Plains, three predominate: The driest—the shortgrass prairie—occurs the farthest west, lying in the Rocky Mountains' rainshadow; mixed prairie takes over farther east, followed by tallgrass prairie in the moister, more fertile east. Between the Sierras and the Rockies, the Great Basin also contains large grasslands, as did California's central valleys before farms took over much of these fertile areas. Extremely dry desert grassland spreads across parts of southern Arizona, New Mexico, and Texas's Big Bend. Small grassland pockets dot parts of the forest-dominated East, including central Florida's prairies, which support isolated peninsular populations of "western" prairie birds, such as burrowing owls and sandhill cranes.
Bison: From Abundance to Absence
On the mixed prairie, where shortgrass and tallgrass prairies
mingle, bison once reigned supreme. The continent's largest
terrestrial animal—standing six and a half feet tall and
weighing up to 2,000 pounds—the bison (Bison
bison) shaped the landscape for at least 4,000 years.
Millions pounded and grazed their way across open land from
Canada south to northern Mexico, and although most abundant
in mixed prairie, they also occurred in short- and tallgrass.
Several Native American tribes followed the bison's movements,
hunting them, revering them, and using virtually all the animals'
parts—their meat, hides, sinews, bones, and even their manure
as a fuel source.
Bison were nomadic, wandering the plains in search of lush pastures, grazing them—often severely—but always moving on, allowing the land to heal. Prairie dogs gravitated to the patches of close-cropped grass left by bison, where sight-lines were clear and they could watch for prowling ferruginous hawks, coyotes, or gray wolves. In turn, bison frequented these extensive prairie dog towns, where they scratched and dust-bathed on open areas maintained by the rodents. Prairie chickens also used these areas as leks, arenas for courtship competitions where males puffed out their orange or pink air sacs and postured for onlooking females.
As the American government thirsted to settle the western frontier, bison eradication became part of the strategy to subdue recalcitrant Native American tribes. In his book, Grassland: The History, Biology, Politics, and Promise of the American Prairie, Montana journalist Richard Manning captures the essence of the struggle. He quotes Native American fighter General Phil Sheridan, who testified to the Texas legislature in the 1870s: "These men [hide hunters] have done more in the last two years and will do more in the next year to settle the vexed Indian question than the entire regular army has done in the last thirty years. They are destroying the Indians' commissary; and it is a well-known fact that an army losing its base of supplies is placed at a great disadvantage."
Taking advantage of markets for hides and meat and the new railroads that snaked across the plains, buffalo hunters blasted away at the seemingly endless herds. Manning cites some staggering statistics: One man killed more than 2,100 bison; one group of 16 men shot down 28,000; between 1872 and 1894, at least 1.3 million hides traveled via rail to city centers. The massacre was among the most dramatic of its kind: In 1830, between 30 and 60 million bison roamed the plains; by 1889, only about 1,000 survived.
As the buffalo dwindled, Native American tribes—troubled by disease, at war with the government, and deprived of their revered bison—suffered greatly. Meanwhile, railroads and expanding trails pushed across the prairie, closely followed by a massive wave of settlement. Land was parceled out to homesteaders and large tracts were given to the railroads to encourage development. In 1837, John Deere's steel plow revolutionized farming, enabling a farmer and horse to bust through the prairie's dense sod. A few years later, cattle drives pushed Mexican cattle north, where they were fattened on cultivated corn. Barbed wire was patented in 1874, enabling farmers to keep cattle away from their crops. The Plains became compartmentalized, a land where cowboys and farmers battled for land. The biggest loser: the American prairie.
Dog Days for Prairie Dogs
On September 17, 1804, not far from the Missouri
River in the Dakotas, Meriwether Lewis wrote of "barking
squirils" that occurred in "infinite numbers and
the shortness and virdue of grass gave the plain the appearance
throughout it's whole extent of beatifull bowling-green in
fine order." A bit earlier in their expedition—the first
U.S.-sponsored expedition to cross the Great Plains—Lewis
and Clark's team had captured, with great difficulty, a barking
squiril, or prairie dog, which they sent back to Thomas Jefferson.
At the time, some five billion prairie dogs in extensive colonies
spread across hundreds of miles of prairie. However, like
the bison, North America's five prairie dog species suffered
greatly as the plains were settled. Ever since cattle first
clopped onto the shortgrass and mixed prairies where these
rodents live, prairie dogs have been labeled pests.
The main problem is that prairie dogs eat grass. Ranchers have long claimed these rodents fiercely compete with cattle for food, an argument with which few conservationists agree. "Evidently, the competition between prairie dogs and cattle is less keen than ranchers would lead us to believe," says John Hoogland, a biologist who has spent many years studying prairie dogs' behavioral ecology. Recent studies estimate that it takes 300 prairie dogs to eat as much as a cow and calf, and that cattle are not seriously affected by sharing grazing land with prairie dogs. "Now we have good evidence that indicates that competition is probably minimal. For the last 150 years we've been shooting and poisoning prairie dogs. It's been a war for all the wrong reasons," says Hoogland.
Outside of national parks, that war continues. After years of shooting and poisoning, North America's prairie dog population has plummeted by as much as 98 percent since the arrival of European settlers. Even the most widespread—the black-tailed (Cynomys ludovicianus)—is in trouble, and conservationists have been pushing to have it listed as threatened on the U.S. Endangered Species List. The more localized Utah prairie dog (Cynomys parvidens) is already considered threatened, while the Mexican prairie dog (Cynomys mexicanus) is endangered. The two other species—the Gunnison's (Cynomys gunnisoni) and white-tailed prairie dog (Cynomys leucurus)—while not endangered, do feel the bite of human encroachment and poisoning.
As their habitat and numbers dip, prairie dogs stranded in isolated prairie patches are especially vulnerable to a microscopic menace—a bacterial disease called sylvatic plague. The plague, which originated in the Old World, was introduced into North America at the beginning of this century. "With prairie dog numbers dwindling, if you get a big outbreak, you could put them below the critical level," says Hoogland. "When it hits, it hits them hard. It usually takes out the whole colony. In Arizona, for example, I lost over 1,000 prairie dogs to plague in less than six weeks."
Saving prairie dogs means saving prairie wildlife. "These animals are the linchpins for western grasslands, and if we don't save them before it's too late, it would be a tragedy," says Hoogland. Other creatures have suffered due in good part to the prairie dogs' decline. A 1993 study by biologists Richard Reading and Stephen R. Kellert that appeared in Conservation Biology, revealed that about 170 vertebrate species depend upon prairie dog activity for survival. For example, the systematic poisoning and shooting of prairie dogs jeopardizes burrowing owls (Speotyto cunicularia), which roost and nest in dog town burrows; mountain plovers (Charadrius montanus), which nest on close-cropped prairie dog "lawns"; and ferruginous hawks (Buteo regalis), swift foxes (Vulpes velox), and endangered black-footed ferrets (Mustela nigripes)—predators that hunt the animals.
The black-footed ferret once flourished, hunting prairie dogs and living in their colonies. Today, this masked, long-bodied predator is one of North America's rarest animals. In the late 1970s, biologists feared it was extinct. Then, in 1981, a small population was found on a Wyoming ranch. However, this population soon dwindled, suffering from outbreaks of sylvatic plague and canine distemper. Between 1985 and 1987, wildlife officials caught the 18 remaining animals, which founded a zoo breeding population. The breeding program eventually brought together the U.S. Fish & Wildlife Service, Wyoming Game and Fish Department, and six institutions, including the National Zoo's Conservation and Research Center (CRC) in Front Royal, Virginia. CRC has played a key role in boosting ferret breeding through artificial insemination. Thanks to recent successes in zoo breeding and subsequent re-introductions, about 200 ferrets now live in the wild in Arizona, South Dakota, and Montana, and plans are underway to introduce them along the Colorado/Utah border. (A program in Wyoming fizzled after disease decimated the animals there.) Meanwhile, about 300 more ferrets live at seven different breeding facilities, including CRC.
Birds of a Feather
Prairie chickens, pin-striped grouse that are not true chickens,
could be considered the bison of the bird world. These grassland-dependent
fowl once flourished, their "booming" courtship
displays inspiring tribal dances and their plump bodies nourishing
Native Americans and European settlers alike. Today, the two
prairie chicken species—the greater (Tympanuchus cupido)
and lesser (Tympanuchus pallidicinctus)—are in trouble.
"We view the prairie chicken as an indicator of prairie
wellness and how it's being treated--which isn't very good,"
says Ronald Westemeier, an Illinois Natural History Survey
wildlife ecologist who is working with other biologists to
reverse the greater prairie chicken's fortune in his state.
While millions of prairie chickens nested on the prairies up until the 1850s, these birds quickly went the way of the bison. "As late as the 1870s, Chicago markets were glutted with prairie chickens in the hundreds of thousands," says Westemeier. At their peak, several million greater prairie-chickens inhabited Illinois. Today, only about 400,000 survive in the entire country, in 11 states. As of the spring of 1998, Illinois hosted only 250 of these. Westemeier and his colleagues have been trying to revive his state's tiny prairie chicken population, which bottomed out at fewer than 50 birds in 1994.
It seemed likely the Illinois birds would follow the heath hen—the East's greater prairie chicken subspecies—into extinction. "The habitat was too small and degraded, which led to lowered genetic variability, which led to lowered fitness," says Westemeier. Today, the picture looks brighter. "We're guardedly optimistic that we'll be successful—at least in the short term," he says of efforts to increase the Illinois birds' fitness by breeding them with translocated prairie chickens from other states. Meanwhile, the lesser prairie chicken, which is far less widespread than its greater cousin, is declining on the dusty shortgrass prairies of southwest Kansas, the Texas and Oklahoma panhandles, southeast Colorado, and New Mexico.
Illinois is also experimenting with grazing cattle on scattered grasslands to control the vigor of such species as big bluestem and Indian grass (Sorghastrum nutans), which previously had been kept low by bison and other herbivores. "The results are looking good," he says, adding, "The main thing you don't want to do is do nothing. If we can't use grazing, we use mowing, burning, or late summer haying." These techniques control the height and density of the grasses, improving habitat for the next season's nesting prairie chickens. Westemeier says the managed grasslands also provide better habitat for other declining prairie nesters, including short-eared owls, dickcissels, and meadowlarks. Meanwhile, other areas are left to grow, accommodating Henslow's sparrows, northern harriers, and other creatures that need tall, dense stands of grass.
Prairie chickens are not the only prairie birds in a tailspin. Many others have steadily declined over the past 30 years, as large, modern farms have replaced prairie and smaller, more traditional farms. Changes in agriculture, such as switching to early-harvest varieties of alfalfa, severely impacted those birds that adapted to nesting in grassy farm fields. Earlier harvests mean nests, eggs, and young are destroyed when the early crop is collected.
Such farm changes, plus development and forest encroachment—the product of farm abandonment followed by fire suppression—have contributed to steady declines. For example, according to the U.S. Geological Survey's North American Breeding Bird Survey, Henslow's sparrow (Ammodramus henslowii) populations have dropped an estimated 93 percent since 1966, and those of bobolinks (Dolichonyx oryzivorus) 37 percent, eastern meadowlarks (Sturnella magna) 53 percent, and grasshopper sparrows (Ammodramus savannarum) 66 percent. Others have held steady, thanks to their differing nesting practices. For example, Oklahoma's state bird, the scissor-tailed flycatcher, remains common across the southern Great Plains. Instead of nesting in the grass, this whitish, pink-sided bird nests in trees and shrubs, many of which have been planted by farmers to buffer wind and conserve soil.
Birds' mobility and flexibility help them take advantage of an initiative designed to revitalize soils—the Cropland Reserve Program of the Farm Bill, which began in the 1980s and was renewed in 1997. This program pays farmers not to plant on about 16 million acres. While the soils rest, the fallow, weedy fields provide grassland birds with suitable nesting habitat. But journalist Manning sees another side to this program: "Farmers were paid to take land out of production and seed it to grass, in most cases crested wheat grass." Unlike native grasses, this now-widespread exotic species does not offer grazers nutritional forage during the tough winter months. It dominates many grasslands, pushing out native species.
Invaders in the Sod
Crested wheat grass (Agropyron pectiniforme), a vigorous
plant native to Asia, was introduced by the U.S. Agriculture
Department in 1916. In those days, a USDA priority focused
on cultivating hardy exotics that withstood the abuse of heavy
cattle grazing. Today, crested wheat grass and other invaders
are among the prairie manager's worst enemies. A hardy plant
called leafy spurge (Euphorba esula) blankets some
2.5 million acres of the upper Great Plains, while many other
areas are covered in non-native crown vetch (Coronilla
varia), blue grass (Poa pratensis), spotted
knapweed (Centaurea maculosa), and a nightmarish
weed called cheatgrass (Bromus tectorum).
Although some exotics were introduced as robust range or erosion-fighting plants, others arrived accidentally. For example, cheatgrass, which hails from Eurasian grasslands, probably reached this continent mixed with imported wheat grains. Once introduced, it thrived and took over prairies. Cheatgrass, it turns out, spreads by fire. After going to seed in summer, it dies. When late-summer lightning strikes occur, extensive stretches of tightly packed, tinder-dry cheatgrass literally provide a welcome mat for fire, catching and spreading flames more readily than native plants. These blazes often burn hotter—and deeper—killing off many native plants adapted to a cooler-burning fire.
By eradicating native flora, cheatgrass cheats wildlife, crowding out valued food and shelter, and providing little forage. Deer, antelope, rabbits, rodents, many birds, and other wildlife cannot live in cheatgrass-dominated habitats. In his book Life Out of Bounds: Bioinvasion in a Borderless World, Worldwatch Institute researcher Chris Bright estimates that in North America, cheatgrass inhabits an area about twice the size of Nebraska, two-thirds of which it dominates. "The rich flora of the sagebrush biome has burned away," writes Bright, "to yield little more than cheat and silence." Bright estimates that in the West, cheat and other introduced rangeland weeds creep onto 4,500 new acres each day.
The onslaught of wicked weeds pushes many prairie champions to seek assistance from an unlikely ally—the chemical industry. Manning's 38-acre property teems with exotics. He writes, "Silent Spring was gospel to a generation of environmentalists, and we came to hate the chemical plague. Then some of us came to hate the plague of exotics even more, and we learned to spray Tordon."
An introduced bush clover called Lespedeza cuneata hounds prairie managers at The Nature Conservancy's Tallgrass Prairie Preserve in Oklahoma. "I've seen it on hilltops and bottoms of valleys," says preserve director Harvey Payne. "Chemicals are about the only way we can control it." Judging by the explosive nature of many exotic plants, chemicals will likely remain in the prairie managers' arsenal for many years to come.
Uncharted Waters
As the Zoo's Fillah and his staff know, re-creating
prairies is a major undertaking. But that is exactly what
many conservationists are doing in areas ranging from National
Park Service-run national grasslands to small private properties.
To succeed, they must revert to the old rules of sporadic
grazing and fire, which keep prairies vigorous and by and
large free of trees. However, these days, fire is considered
something to be controlled, and grass is something most people
associate with their home lawns. "They say nothing succeeds
like succession," adds Westemeier. "If you're managing
grasslands, you can't fight the woodies without prescribed
burning, grazing, mowing, haying, that whole bit."
Much remains to be learned about prairies and how to revive them. The Conservancy's Payne is up for the challenge. "The tallgrass prairie is an ecosystem we don't know much about because it's basically been extinct since the buffalo were extirpated," he says. So, in a sense, the Conservancy's preserve, a reclaimed cattle ranch, is an experiment like the Zoo's tiny prairie parcel, but on a grander scale. "We have the only tallgrass prairie preserve of sufficient size to recreate forces at a landscape level," says Payne. "Our goal is to recreate a functioning ecosystem and all the forces that created it so it can continue to evolve."
Bison, of course, are central to this scheme. In 1993—only four years after The Nature Conservancy bought the land—300 buffalo were released in the tallgrass prairie. Today, 750 roam 11,000 acres of the 38,500-acre reserve. Their numbers are growing, but carefully maintained, and surplus animals are sold off each year. "Five or six years from now," says Payne, "we will have 32,000 acres open to the bison and the herd will probably grow to 2,200." The Conservancy is not the only group reintroducing bison. Several Native American tribes are enthusiastic about releasing them on reservations, and media mogul Ted Turner and many other buffalo ranchers raise them for profit. They require less care than cattle, and their trendy lean meat fetches more money than beef. About 150,000 buffalo now inhabit North America, most owned by ranchers. The federal government administers about 5,000 on parkland, and its largest free-ranging herd—more than 3,000 animals—lives in Yellowstone National Park.
For comparison, The Nature Conservancy allows 7,700 head of cattle to graze some 15,000 acres, while several thousand acres remain free of large grazers, as a control. Diet studies revealed that local buffalo diets consist of 99 percent grasses, as opposed to 80 to 85 percent of the cattle's diet. The balance of the cattle's attention went to forbs. Payne points out that while the difference between bison and cattle diets may not seem large at first, it can be significant over the years. Even if lands are not overgrazed, cattle will target favorite plants until they eradicate them.
Fire, carefully applied at different times of year, forms the second key ingredient in the Tallgrass Prairie Preserve's grassland resurrection. Three distinct prescribed burns sweep across the prairie each year: spring fires, emulating those once regularly set by lightning and Native Americans; less intense late summer blazes, usually sparked by lightning; and mid-October conflagrations once commonplace during this most fire-prone month.
The third ingredient—climate—regulates itself. The preserve's tallgrass prairie receives a generous 36 to 38 inches of annual rainfall, enough to transform the rolling prairie into scrubby woods if not for the burns. But Payne and his colleagues won't let that happen. Like the Zoo's Fillah and his coworkers, they are committed to succeeding at the great prairie experiment. Payne seems to enjoy the unique project he heads. He's not alone—he says the preserve will soon host more than 50 new research projects that aim to solve the prairie's many mysteries. "We're, to a large extent, sailing into uncharted waters," says Payne, with the giddy anxiety of a departing explorer.
ZooGoer
28(3) 1999
Copyright 1999 Friends of the National Zoo.
All rights reserved.
