Restoring Great Plains grassland landscapes

By Terry Zene Riley, Ph.D.

The Great Plains is a broad expanse of grassland that lies east of the Rocky Mountains in the United States and Canada, covering all or portions of the U.S. states of Colorado, Iowa, Kansas, Minnesota, Montana, Nebraska, New Mexico, North Dakota, Oklahoma, South Dakota, Texas and Wyoming, and the Canadian provinces of Alberta, Man­itoba and Saskatchewan. The Great Plains has undergone significant changes over the last three centuries (Table 1). Most significantly, much of these grasslands has been converted to cropland for the production of corn, soybeans and wheat. Producing energy, food, feed and fiber, this cropland can yield relatively high financial returns to landowners, agricultural producers, agribusinesses and rural economies. However, native grasslands in the Great Plains have also proven a valuable resource for livestock grazing and forage (hay) production; recreational opportunities (i.e., hunting, fishing, trapping and wildlife viewing) and environmental benefits (i.e., reducing soil erosion, improving water quality, increasing carbon sequestration and providing wildlife habitat). In particular, grasslands provide habitat for threatened, endangered and other at-risk species. Converting grasslands to accommodate these other uses, however, has resulted in a loss of functional habitats for a broad range of native grassland species.

Conservation of native grassland not only contributes to the maintenance of biological diversity but also more specifically provides habitat for wildlife. The unique avian assemblages associated with grasslands in the Great Plains are in danger—grassland bird populations have shown steeper, more consistent and more geographically widespread declines than any other guild of North American bird species. Breeding Bird Survey (BBS) data from 1966–1993 indicate that almost 70 percent of the 29 grassland bird species adequately surveyed by the BBS had negative population trends. The populations of favorite grassland birds like the western meadowlark (Sturnella neglecta), the dickcissel (Spiza Americana) and the lark sparrow (Chondestes grammacus) are declining. The conversion of native grassland to other uses, including introduced grasses for livestock forage, can change the structure and function of habitat such that it can no longer support native wildlife species. Furthermore, the fragmentation of the remaining native grassland areas in the Great Plains may reduce their habitat value, resulting in these areas not being large enough or close enough to each other to support their natural biodiversity. The net effect of these impacts has been a substantial decline in the health of grasslands of the Great Plains, leading them to be identified as among America’s most endangered ecosystems.^1,2

Native flora and fauna within the Great Plains evolved with and adapted to the historical ecosystem diversity of the area. Historical disturbance regimes have been altered, however, in most grassland areas of the Great Plains, resulting in plant communities now having different compositions, structures and processes than they did historically. To restore and maintain the composition, structure and processes of grasslands within the Great Plains, an approach must be selected that evaluates the health of existing ecological communities and conditions relative to the healthy ecosystem diversity that was present three centuries ago.

There is a strong scientific foundation for using a historical reference for defining ecosystem diversity. Describing and understanding a representation of this historical diversity is perhaps the only effective method of providing for the habitat needs of grassland-dependent species, many of which are not well known. Historical ecosystem diversity in the Great Plains was formed by two primary factors: (1) different ecological sites (abiotic) that support different plant and animal communities and (2) disturbances that influenced the composition and structure of the plant community, including climate change. Under­standing the type, distribution and dynamics of these ecosystems is fundamental to managing or restoring ecosystem diversity across the Great Plains.³

Ecosystems have been and continue to be directly altered by human actions. Although Native Americans interacted and influenced ecosystems for thousands of years, the greatest and most drastic changes, and those of greatest conservation concern in the Great Plains, have occurred only over the past 150 years. Scientists recently have begun to understand the implications of these alterations to and interruptions of historical disturbance regimes in the Great Plains. Recent studies have shown that the suppression or cessation of these disturbances has changed ecosystem processes, and ultimately the composition, structure and function of many ecosystems. Therefore, in order to identify those ecosystems and/or habitats in need of conservation, important reference information must be researched and produced, including a description and assessment of historical conditions as influenced by historical disturbance regimes in the Great Plains. This information can then be used to compare historical conditions to current land-use patterns to identify critical remaining areas of intact or “natural” grassland systems in the Great Plains. Additionally, these data will highlight those areas with the greatest restoration potential.

Three primary historical disturbance regimes have been identified for grasslands in the Great Plains: climate, fire and grazing. The climatic pattern is cyclical between wet and dry periods, causing changes in plant species composition and structure. Fire was a relatively common disturbance prior to European settlement. As a result, most grasslands exhibit a number of characteristics that are well suited to a fire-prone landscape. Grazing, particularly by bison (Bos bison), also contributed to shaping the grassland ecosystem diversity of the Great Plains.

A framework for addressing ecosystem diversity for grasslands across the Great Plains should include a classification of all ecosystems that occurred historically within each Major Land Resource Area (MLRA)⁴ in the U.S. or Soil Correlation Areas (SCA)³ in Canada. An analysis of soils maps can be used to quantify the amounts of each ecological site within each MLRA or SCA. Additional mapping analysis can determine the amount of land in each ecological site that has been converted to cropland, urban development, exurbia or other human uses. Information on the existing conditions of plant communities within the Great Plains does not exist nor have data on its untilled grasslands been documented on a consistent enough basis. This information is, however, critical for grassland conservation, without which the existing levels of representation of historically occurring ecosystems cannot be quantified.

Through the use of such a classification system and accompanying analyses, the ecosystem-diversity approach can be used to identify conservation objectives. The goal of such an approach would not be to return grassland landscapes in the Great Plains to historical conditions. Instead, the historical reference would help set specific objectives to restore and maintain healthy grasslands, including the native biodiversity of grassland-dependent flora and fauna. An initial goal for ecosystem representation in the Great Plains might be to restore and maintain at least 10, 15 or 20 percent of the historical conditions for all ecosystems in each of the 46 MLRAs in the United States and nine SCAs in Canada. The restoration and maintenance goals of 10, 15 or 20 percent are dependent on the desired status of grassland-dependent wildlife species, with higher levels occurring in areas where a richer diversity of wildlife is desired. The minimum 10 percent level of native grassland representation within an area often has been used as a conservation goal under various national and international ecosystem restoration programs. The assumption is to put the greatest focus on those areas where functional grassland ecosystems still occur, as well as maintain the quality of these areas. Although 10, 15 or 20 percent are identified as minimum levels of grassland representation, maintaining levels greater than these amounts often is preferred. As better information is obtained on the historical ecosystems and status of existing conditions, ecosystem representation goals and their prioritization for restoration can be revised and updated to reflect this improved knowledge.

Nearly 80 percent of the historic grasslands occurring in the Great Plains have been converted to other uses. These changes have resulted in a loss of functional habitats for a broad range of native grassland species. Restoring and maintaining grassland ecosystem diversity within the Great Plains are critically important in order to avoid the consequences of many threatened and endangered native wildlife and plant species. The long-term conservation of Great Plains grasslands requires the integration and implementation of conservation efforts at local, state, provincial and range-wide levels. A grassland conservation plan is needed to identify threats, issues and strategies and to provide a comprehensive framework that facilitates the restoration and maintenance of grassland ecosystem diversity within the Great Plains.

Notes

1. Noss, R. F., E. T. La Roe, III, J. M. Scott, “Endangered Ecosystems of the United States: A Preliminary Assessment of Loss and Degradation,” “USDI, National Biological Service, Biological Report 28” (1995)

2. F. B. Samson and F. L. Knopf, “Prairie Conservation: Preserving North America’s Most Endangered Ecosystem” (Washington, D.C.: Island Press, 1996)

3. W. L. Vodehnal and J. B. Haufler, Compilers, “A Grassland Conservation Plan for Prairie Grouse,” (Fruita, Colo.: North American Grouse Partnership, 2007)

4. United States Department of Agriculture (USDA), “Land Resource Regions and Major Land Resource Areas of the United States, the Caribbean, and the Pacific Basin,” “U.S. Department of Agriculture Handbook” 296 (2006)

Additional literature

United States Government Account­ability Office (GAO), “Agricultural Conservation: Farm Program Payments Are an Important Factor in Landowners’ Decisions to Convert Grassland to Cropland,” (GAO-07-1054, a report to congressional requesters, 2007)

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