The Great Plains As a Natural Region: the Basics

Proceedings of the South Dakota Academy of Science,Vol. 80 (2001) 259

THE GREAT PLAINS AS A NATURAL REGION: THE BASICS

Richard A. Peterson Wewela, SD 57578

ABSTRACT

The need for this paper became apparent during a review of articles in the Prairie Naturalist(1986-1995), where the term, Great Plains, was used to de- scribe many different areas/regions, most of which were outside of established natural boundaries. The Rocky Mountains have long been the agreed upon western boundary of the Great Plains and the primary factor in the development of the Great Plains; indeed, without the uplift of the Rocky Mountains there would not be a Great Plains region. Consistent natural boundaries for the Great Plains, were in general use after 1931, when Nevin M. Fenneman described the region in Physiography of the Western United States, and reafﬁrmed the eastern boundary as originally ﬁxed by John Wesley Powell in 1895. Typ- ical Great Plains landforms (plains and buttes) have resulted from the mountain uplift and subsequent sediment deposits that increased the elevation of the Great Plains relative to the Central Lowlands. The Great Plains, in the rain shadow of the Rocky Mountains, have been characterized by a dry subhumid to semiarid climate. The potential natural vegetation of the Great Plains has been, since the last retreat of the continental glaciers 8,000-10,000 years ago, grass/forb vegetation - mostly a mix of mid and short grasses. True Prairie has been limited to the moist side of the dry/moist boundary. These differences between the grasslands of the Great Plains and the grasslands of the Central Lowlands have resulted in differences in occurrence and abundance of grassland animal species, such as black-tailed prairie dog, black-footed ferret, swift fox, pronghorn, ferruginous hawk, prairie falcon and lark bunting. The eastern limits of these species more or less coincides with the eastern boundary of the Great Plains physiographic region and the dry/moist boundary. Given the differences described here it would be more accurate and appropriate to limit the use of the term, Great Plains, to the western Interior Plains and divide the Midcontinent grasslands into eastern (True Prairie) and western (Great Plains) sections.

Keywords

Great Plains, natural, boundary

INTRODUCTION

The Great Plains! As part of an article title the term is a real eye catcher. Is the Great Plains a real place with distinctive characteristics and limits, or is 260 Proceedings of the South Dakota Academy of Science,Vol. 80 (2001) it just a handy term useful to authors to convey an image? If it is a specific region, what are the characteristics and where are the boundaries? If it is just an image, of what? Observant westbound travelers upon approaching the Great Plains may notice an abrupt rise in elevation as they encounter the escarpment of the Coteau du Missouri. Elsewhere, travelers may note the gradual change from landscapes of rolling surfaces, and hazy views of rounded hills, to landscapes of broad flat plateaus and flat surface remnants, where the skyline is distant and clear—welcome to the wide open spaces—welcome to images of cowboys and Indians, wagon trains, immense buffalo herds, homesteaders, drought and hardship. The term Great Plains was not much used as a regional designation until 1857, when it was used in promotional articles and speeches synonymously with “pastoral region” by William Gilpin, who was appointed, in 1861, first gov- ernor of Colorado Territory. His purpose was to create a more positive image to promote settlement in the Great American Desert, as the area was generally known at the time (Lewis 1966). Since Gilpin, the Great Plains of North America have been recognized as both a natural and a cultural region by schol- ars in various disciplines (e.g. geology, biology, geography and history); how- ever, consistent boundaries for the area, and its name, Great Plains, were not in general use until after 1931, when Nevin M. Fenneman described the region in Physiography of the Western United States, and reaffirmed the eastern boundary as originally fixed by John Wesley Powell in 1895. Prior to this the region had most often been referred to as the High Plains to distinguish it from the lower Prairie Plains of the Midwest (Brown 1948). More recently it has become common to find the term, Great Plains, used by many natural science authors to refer to many different regions - both natural and artificial, as was found from a review of articles in The Prairie Natu- ralist (1986-1995). As well, the Great Plains Research journal does not limit it- self to the Great Plains, but includes in its sphere most of central North Amer- ica: grasslands, savannahs, and some forest. Books, such as Flora of the Great Plains and Birds of the Great Plains, include portions of other natural regions and exclude portions of the Great Plains natural region. The term, Great Plains, is also used to designate artificial regions with no apparent natural pa- rameters, as in “Great Plains states.” Is it appropriate in natural science writing to use the term, Great Plains, that has been previously recognized as the name of a specific natural region and apply it to artifical regions? It would be simpler if the so-called Great Plains states were entirely within the Great Plains natural region, unfortunately no state is entirely within the Great Plains. Many of these Great Plains states could just as easily be called Central Lowland states, or True Prairie states, and others could be included as Rocky Mountain states. The problem (in my opinion) that has developed by applying the term, Great Plains, to many different areas, is that now when it is used without ex- planation or a map, no one can be certain as to what area or region the au- thor is referring. The following presentation describes the Great Plains as a natural region with unifying characteristics: physiographic, climatic, and veg- etative. Proceedings of the South Dakota Academy of Science,Vol. 80 (2001) 261

GREAT PLAINS PHYSIOGRAPHIC CHARACTERISTICS

The Great Plains physiographic province is located in the western portion of the Interior Plains Physical Division of North America (see Fig. 1). It is different from the eastern portion of the Interior Plains (the Central Lowlands) mostly because of the development and continued presence of the Rocky Mountains which are the western boundary of the Great Plains. The marine sediments of the upper Cretaceous strata underlying the Great Plains were tilted by the uplift of the Rocky Mountains and then covered by sediments (Ter- tiary strata) that eroded from the mountains. Subsequent uplifts caused the streams that had been depositing sediment on the plains for more than 60 mil- lion years to cut down into these sediments, more or less beginning the cre- ation of the current land- scape with its streams, buttes, badlands, breaks and occasional broad plateaus (e.g., Staked Plains) left between the streams, according to Trim- ble (1980). More recently in geologic time an area unique to the northern Great Plains was created by a dead-ice moraine that covers a high- land area called the Coteau du Missouri. This coteau is the eastern limit of the sediments brought by rivers Figure 1. North American Interior Plains physio- from the Rocky Mountains. graphic region divided into the Great Plains and An escarpment, several the Central Lowlands, adapted from Trimble hundred feet high separates (1980). the Coteau du Missouri from the lower, nearly ﬂat, drift-covered plains of the Central Lowland physiographic province to the east. This glaciated portion of the Great Plains includes the area north and east of the Missouri River. Continental ice sheets did cover some areas south and west of the current Missouri River, but only scattered boulders remain to indicate the glaciers former presence, and current conditions there are more simi- lar to the unglaciated portions of the Great Plains than to the glaciated areas east of the river. The areas of the Great Plains regions covered by glaciers and other nontypical conditions are shown in Figure 1.

Summary of Great Plains physiographic characteristics: 1. The mountain uplift tilted the upper Cretaceous strata and this, along with sediment deposits from the mountains increased the elevation of the Great Plains relative to the Central Lowlands. 262 Proceedings of the South Dakota Academy of Science,Vol. 80 (2001)

2. Most of the Great Plains were not glaciated. 3. Typical landforms include: large ﬂat surfaced remnants (plains) and small ﬂat surfaced remnants (buttes).

GREAT PLAINS CLIMATE CHARACTERISTICS

The distinguishing climatic characteristic of the Great Plains environment is a deficiency of water. “This deficiency accounts for many of the ways of life in the West. In this deficiency is found the key to what may be called the plains civilization. It is the feature that makes the whole aspect of life west of the 98th meridian such a contrast to life east of that line (Webb 1931: 17).” And again: The Great Plains has a climate which distinguishes it from neighboring regions, and according to Borchert (1971) the most distinctive characteristics are the great droughts that have temporarily extended the arid climate of the Southwest into the Great Plains, and pushed the semiarid climate of the Great Plains eastward into the Prairie region. Average annual precipitation in the Great Plains decreases from east to west, being least, approx. 12 inches (30cm), at the base of the Rocky Moun- tains. This is the result of the rain shadow effect of the mountains and in- creasing distance from the main moisture source, the Gulf of Mexico. The location of the moisture deficit line, the division between the moist subhumid and the dry subhumid of Thornthwaite’s (1948) moisture regions (Fig. 2) can vary depending on what time period is used for the calculation as described by Borchert (1971). The annual variability of the moisture makes any short term dry/moist boundary somewhat tentative, but the long term average location of the moisture deficit line coincides well with the eastern boundary of the Great Plains physiographic province indicated in Figure 1, and even better with the mixed grass/tallgrass boundary of Figure 3. Temperature plays an im- portant role in determining if a particular place has a moisture deficit. In the Great Plains, as would be expected, the annual tem- peratures are coolest in the north and warmest in the south; therefore, it takes less rainfall in the north for a location to be in the moist region.

Figure 2. Moisture regions of the Interior Plains, adapted from Thornwaite (1948),Trewartha (1957), and Bailey (1979). Proceedings of the South Dakota Academy of Science,Vol. 80 (2001) 263

Summary of Great Plains climate characteristics: 1. A moisture deﬁcit caused primarily by the rain shadow effect of the mountains—dry subhumid to semiarid climate. 2. The lower humidities increases clarity of the air—much less haze than the Central Lowlands.

GREAT PLAINS GRASSLANDS VEGETATION CHARACTERISTICS

The fact, that the Great Plains, was for all practical purposes—treeless, was in part responsible for its original image of infertility. “Scarcity of wood and water: two of the three legs of civilization,” was generally considered to make settlement by an agricultural people impossible and the area suited only for pasturage (Webb 1931: 9). The Great Plains are part of the Grassland Biome of North America and have been so since the retreat of the continental glaciers and the warming of the climate some 8,000-10,000 years ago (Kaul 1986). Most descriptions of the “Mid-continent prairie” (Costello 1969: 38) distinguish between the “true prairie” in the east and the “mixed prairie” in the west (Eyre 1968: 107, and Costello 1969: 38) or true prairie (tall) and Great Plains grasslands, mid and short (Weaver 1968); some add a short grass zone in the drier western section adjacent to the Rocky Mountains (Brown 1985), and a separate category for the unique sandhills grasslands (Kaul 1986). The distribution of potential plant community types depicted in Figure 3 is adapted primarily from ( Kuchler 1964). A distinction is made by most authorities between the tall grass (true prairie) and the western portion of the Midcontinent grasslands characterized as mixed and short in Figure 3. Some ecologists consider the mixed grass prairie to be a broad transition zone in which the tall grasses of the true prairie mingle with the shorter grasses of the Great Plains (Borchert 1971 and others) in decreasing proportions to the west. This seems to be the most realistic view of the Great Plains grasslands given the dynamic nature of the plant environment with variable annual rainfall combining with variable grazing intensities to create a complex mix- ture. Eastern Nebraska contains the only large area of tall grass prairie within the Great Plains physiographic province; it is also the only area where the dry/moist boundary is within the Great Plains physiographic province. Figure 3. Potential natural vegetation of the mid- This is an area with a deep continent grasslands, adapted from Kuchler covering of loess which (1964), and others in Lauenroth et al (1999). 264 Proceedings of the South Dakota Academy of Science,Vol. 80 (2001) merges with the sandhills to the west. Some authorities include the sandhills with the tall grass area to the east, but it is well west of the dry/moist boundary and better left as a unique area within the Great Plains natural region. It should also be noted; that although, trees are not a part of the typical Great Plains potential natural upland vegetation, tree growth does indicate an- other difference between the True Prairie regions and the Great Plains. In the Great Plains a considerable effort; including planting, cultivation and irri- gation, is needed just to get trees started, let alone growing well. While in the true prairie, trees are natural invaders of the grasslands and prior to settlement were kept out by frequent ﬁres, both natural and manmade.

Summary of Great Plains grasslands potential natural vegetation characteristics: 1. Grass/forb vegetation dominant: mostly a mix of mid and short grasses; although, tall grass species may be found in scattered favorable (moist) locations. True (tallgrass) Prairie is limited to the moist side of the dry/moist boundary (e.g., the Flint Hills are not within the Great Plains natural region). 2. Upland shrub communities do occur: sandsage/yucca on sandy soils in the central plains, silver sage in the northern plains, desert shrubs en- croach from the southwest, and big sagebrush encroaches from the in- termountain west into the northern plains.

DISCUSSION

None of the information presented above is new, and it is probably well known by most people writing about the Midcontinent grasslands: So why aren’t the natural regions more widely used in the literature? Maybe too much attention has been paid to the vegetation: “hey, its all grasslands, whats the big deal.” Well, it is apparently a big deal to the species whose eastern range limits more or less coincide with the eastern boundary of the Great Plains physiographic province and the dry/moist boundary, such as black-tailed prairie dog, black-footed ferret, swift fox, pronghorn, ferruginous hawk, prairie falcon. Other species, like the bison, formerly reached their greatest abundance in the Great Plains. One of the best indicator species of Great Plains conditions is the lark bunting whose normal breeding range boundaries nearly coincide with the boundaries of the natural region (National Geographic Field Guide 3rd edi- tion). The lark bunting is found in significant numbers east of the region only during dry periods. The range of these animals is more likely to extend west from the Great Plains than into the more moist conditions to the east. As well, it is only with great effort that shelterbelt trees can be started in semiarid grasslands, while east of the dry/moist boundary the concensus seems to be that trees and shrubs were kept from taking over the original tallgrass prairies only because of the effects of fire. In addition to moisture and vegetation, landforms are a significant factor in determining the distribution many animal species (e.g. prairie falcons nesting on buttes). Proceedings of the South Dakota Academy of Science,Vol. 80 (2001) 265

There are some well established and long recognized natural divisions within North America, such as the Great Plains. It is unfortunate that this term long associated with a speciﬁc natural region has been used inappropriately in so much of the current scientiﬁc literature relating to wildlife, with many different areas being referred to as the Great Plains. The confusion that can develop with the current practice of inappropriately, and with great frequency, dropping geographic terms willy - nilly into articles could be eliminated if ex- isting precedents, as outlined in this article, are considered before publishing.

CONCLUSION

The purpose of this presentation is to remind natural scientists of the ex- isting precedents about the location of the Great Plains natural region and to encourage them to be careful when using the term, Great Plains, in the future. In my opinion it is most accurately and appropriately used for referring to the Great Plains natural region which can be deﬁned by the following 3 conditions:

1. Within the Great Plains Physiograpic province as shown in Figure 1. 2. West of the dry/moist climate boundary shown in Figure 2. 3. Its dominant potential natural vegetation consists of mixed grasses (mostly mid and short) or short grasses as indicated in Figure 3: exceptions are made for special conditions like the Nebraska sandhills.

Separating the Midcontinent grasslands into eastern (moist—True Prairie) and western (dry—Great Plains) sections, and using these subdivisions when generalizing about tree coverage, species occurrence, species abundance, habitat associations, etc., would seem to be more accurate and appropriate than the current situation.

LITERATURE CITED

Bailey, H.P. 1979. Semi-arid climates: Their deﬁnition and distribution. In Agri- culture in Semi-Arid Environments, ed. A. E. Hall, G. H. Cannell and H. W. Lawtion, 73-97. Berlin: Springer-Verlag. Borchert, J. R. 1971. The dust bowl in the 1970’s. Annals of the Assoc. of Am. Geog. 61: 1-22. Brown, R. H. 1948. Historical geography of the United States. Harcourt, Brace & World Inc. New York. Brown, L. 1985. The Audubon Society nature guides: grasslands. Alfred A. Knopf, Inc., New York. Bystrak, D. 1981. The North American breeding bird survey. Studies in Avian Biology. 6:34-41. Costello, D. F. 1969. The prairie world. Thomas Y. Crowell Co., New York. Eyre, S. R. 1968. Vegetation and soils, 2nd ed. Aldine Publishing Company, Chicago. 266 Proceedings of the South Dakota Academy of Science,Vol. 80 (2001)

Fenneman, N. M. 1931. Physiography of the western United States. McGraw- Hill Book Co. Inc., New York and London. Kaul, R. B. 1986. Flora of the Great Plains. Great Plains Flora Assoc. Univ. Press of Kansas, Lawrence Kuchler, A.W. 1964. Potential natural vegetation of the conterminous United States. Am. Geog. Soc. Sp. Publ. 36. Lauenroth, W.K., I.C. Burke, and M.P. Gutmann. 1999. The structure and func- tion of ecosystems in the central North American grassland region. Great Plains Research. 9: 223-259. Lewis, M. G. 1966. William Gilpin and the concept of the Great Plains region. Annals of Am. Assoc. of Geog. 56: 33-51. Thornthwaite, C. W. 1948. An approach toward a rational classiﬁcation of climate. Geographical Review. 38: 55- 94. Trewartha, Glenn T. 1957. Elements of Physical Geography. McGraw- Hill Book Company, Inc., NY,NY. Trimble, D. E. 1980. The geologic story of the Great Plains. US Geol. Survey Bull. 1493. USGS, Washington, DC. U.S. Dept. of Agric. Soil Conservation Service. 1981. Land resource regions and major land resource areas of the United States. Agric. Handb. 296. Wash- ington, DC: U.S. Dept. of Agric. Weaver, J. E. 1968. Prairie plants and their environment. Univ. of Nebraska Press, Lincoln. Webb, W. P. 1931. The Great Plains. Ginn and Company, New York.