ISSUE PRIMER

DETAILED REPORT

- - - - INTERNATIONAL

- - - - NORTH AMERICA




Protected Areas of the Great Plains

The Great Plains are home to the ponds, "potholes," and other wetlands that provide critical nesting habitat for millions of ducks, shorebirds, and geese. An estimated half of all North American waterfowl production occurs in the prairie pothole region. Nowhere else in the continent are there so many protected areas ideally suited to the nesting requirements of migratory waterfowl. Giant Canada geese, once believed extinct, are plentiful nesters on the 120 islands of Lake Audubon in the Audubon Refuge of North Dakota. Trumpeter swans, formerly close to extinction, are abundant at Lacreek in South Dakota. Some of the largest wintering concentrations of bald eagles occur at Squaw Creek in Missouri. During the spring and fall migrations, many of the refuges are home to millions of birds, as at Sand Lake in South Dakota, where 2 million of the midcontinental population of snow geese come through in spring. By fall, the refuge may be a temporary home to a half million Franklin's gulls, a quarter million mallard ducks, 5,000 tundra swans, and 12,000 pelicans. Incredibly, half the shore birds in North America are believed to stop at Quivira or nearby Cheyenne Bottoms in Kansas during annual migrations. In addition, many refuges provide the last remaining habitat for the unique prairie flora and fauna that once teemed across the plains. Refuges such as Sullys Hill in North Dakota and Fort Niobrara in Nebraska are home to remnant populations of buffalo, sharp-tailed grouse, prairie chickens, and prairie dogs. Other refuges, such as Walnut Creek in Iowa, are the sites of attempts to restore the endangered prairie ecosystem (Riley and Riley 1992). Far to the north, at the edge of the prairie in Canada, Prince Albert National Park in Saskatchewan and Riding Mountain National Park in Manitoba provide a unique blend of grassland, parkland, and boreal ecosystems.

Water, and the productivity that it brings, is the lifeblood of the prairie. The abundance of wetlands is in turn closely tied to the weather; interannual variation in climate, including both precipitation and temperature, was found to explain more than 60% of the variation in the number of wetlands from year to year (Larson 1995). This variation has important implications for migrants such as the pectoral sandpiper, one of several sandpiper species that funnels its migration through the Great Plains (Farmer pers. com., see also Weins and Farmer in press). The birds arrive in the early spring, on their way from their wintering grounds in South America to breeding grounds on the northern coast of Alaska and Canada. During their stopover, the birds feed heavily and dramatically increase their energy reserves for the remaining flight to the north. When they arrive in mid-April, body fat typically makes up only 10% of their total weight; five weeks later, it is more than 40%. In dry years, the wetlands they need for feeding are not as abundant, and the birds are not able to put on as much weight. In 1994, for example, an extremely dry year, females arrived with close to the typical 10% of body fat, but as the season progressed, most lost weight. As a result, many did not go north at all and failed to breed (Farmer pers. com.). Research indicated that the sandpiper's foraging activity was concentrated not only in refuges, but in the temporary ponds and moist areas found in agricultural fields (Farmer pers. com.). In a dry year such as 1994, fewer of these small moist areas are to be found. To compound the situation, farmers are able to till their fields earlier, resulting in even fewer temporary wetlands.

Global warming due to the greenhouse effect brings another threat to the region, which in combination with the relentless agricultural development that has led to steady declines in wetlands and waterfowl abundance (Bethke and Nudds 1995) appears likely to be particularly devastating. In one recent analysis in which scientists linked several state-of-the-art climate change models with a suite of ecosystem models, the most consistently threatened protected areas in the conterminous U. S. were the National Wildlife Refuges of the central part of the country (Appendix 1). Ecosystem quality consistently declined in the landscapes surrounding the refuges, in many cases dramatically so. These models demonstrated that the central U.S. is especially sensitive to greenhouse warming, and that widespread ecosystem transformation in the prairie is a consistent prediction of increased greenhouse gas concentrations.

In a detailed hydrological study of potential climate change impacts on a typical small prairie wetland (Poiani and Johnson 1993), warmer annual temperatures similar to those predicted by various climate models resulted in drier conditions, quite irrespective of whether more or less precipitation was received on average. The result was less open water and greater vegetative cover. The study is especially troubling because it suggests that smaller wetlands would be especially vulnerable to global warming. These smaller wetlands are disproportionately important for waterfowl. When the ratio of vegetation cover to open water is close to unity, as is typical of small prairie potholes, breeding bird density and diversity is at a maximum (Diamond and Brace 1991, Poiani and Johnson 1991). As well, the persistence of the temporary wetlands into the early summer importantly influences brood survival and hence production of the next generation (Diamond and Brace 1991).

Of course, migratory birds of the Great Plains are expert at dealing with the variability in conditions found from year to year and region to region. Typically, as they arrive from the south, the birds settle down in the first good habitat that they find. In a dry year in the prairie, they may move north into the forest transition zone of Alberta, Saskatchewan, and Manitoba, where wetlands are even more abundant (Larson 1995). Again however, climate models provide little hope for the continued success of age-old strategies. Models suggest that the prairie parkland will also be hard hit by global warming. These wetlands appear to be even more sensitive to warming than prairie potholes, perhaps because of the evapotranspirative demand of the willows and other tree species that border the wetlands (Larson 1995).

The net effect of global warming thus appears to be a steady decline in the amount of habitat available to the millions of waterfowl that make use of the prairie region. Avian biologists suspect that an early warning of the decline will be increased transmission of avian botulism and large-scale die-offs as more and more birds are packed into increasingly rare habitat (Price pers. com.). The implications of loss of duck breeding sites and population declines in the Great Plains region could be very serious for the millions of Americans who engage in recreational duck hunting, and for the outfitting industry they support.

In addition to the ubiquitous waterfowl, many bird species make use of the upland prairie itself. Already, these grassland species show some of the steepest declines of all bird species monitored in the Breeding Bird Survey (Price et al. 1995), and a recent study suggested further problems in a warming world. The study made use of the often-strong relationship between a species' geographic range and regional climate patterns to predict range shifts under a scenario of global warming (Price 1995). Under doubled CO2 concentrations, all 23 grassland species showed range shifts and approximately half showed a range decline. Two were predicted to become extinct (Sprague's pipit and McCown's longspur), and a two others were highly vulnerable (chestnut-collared longspur and Baird's sparrow). Almost all species showed range shifts to the north, into regions that at the moment are mostly forest. Within the time frame of the predicted warming, significant conversion to grasslands was viewed as unlikely, hence the size and fragmented nature of the existing grassland patches in the north would put an additional burden on populations (Price 1995). Shifts such as these will be stronger for some species than others, resulting in a state of flux in the species mixtures from site to site. The resulting changes in competitive interactions among species may lead to further changes in community composition.

Increasing concentrations of atmospheric greenhouse gases and associated global warming does not bode well for prairie ecosystems and their abundant wildlife populations. Many prairie species have suffered enormous declines in the past; some are currently declining, and others are barely able to hold their own in the face of existing development pressures. Protection and restoration can and have done much to improve the situation, but unfortunately will provide little respite in a world of radical climate-induced ecosystem reassortment.