The myth of cattle as "replacements" for historic grazers

Plenty of times around here you'll hear justifications for cattle ranching as simple "replacement" for (if not Manifest Destiny-ordained) historic grazers of the Great Plains, particularly bison. While there are certainly some similarities, overall this is a poor argument--particularly when you move into the Great Basin and Intermountain West where there is little if any evidence of any heavy historic grazing pressure (e.g. absence of dung beetles).

I always believed that there were important differences between bison and cattle, but I found it tough to nail down specific factual support. Below is a short paper by ecologist George Wuerthner on this very issue, which makes quite the strong case for why bison and cattle impact range differently. And of course these differences are compounded by the way we ranch cattle--in limited enclosures that tend to amplify and concentrate cattle impacts in specific areas for specific time periods.

Wuerthner further explains (in response to my questions about what we know about how soon/frequently migrating bison would "return" to an area once they (often severely) grazed it):

Your perception that bison are different than cattle is correct. I hear that line all the time that since bison grazed the plains, well cattle are just a natural substitute. That's like saying polar bears and black bears are the same just because both are bears. There are huge evolutionary difference between bison and cattle.

The frequent movement of bison you mention below is one of them. For seemingly unknown reasons, bison move and often far distances. So while they might graze a place severely, they leave it alone for long periods of time. How long probably had more to do with many factors. For instance, some routes were natural corridors for migration and these might have been hit more frequently, but in other cases, they might not regraze a particular area for decades. So fencing in animals like cattle makes things even worse.

Historical accounts tell of big herds moving across the horizon, but you can also find many historical accounts where people did not encounter any bison for long, long distances. For instance, Lewis and Clark are always used to show how abundant bison were on the plains--people look at their outward journey up the Missouri where they did encounter quite a few bison (though the largest herd they saw was about 10,000 not the "millions sometimes quoted). But on Clark's return he traveled from Missoula in western Montana to nearly Billings, Montana before he saw any bision--that's about 400 miles. Not one bison! Though they did see bison trails, etc. showing that bison were occasionally in the area.

Secondly, bison use the plants differently. They can survive on less nutritious forage. They spend less time in riparian areas. etc.

'Speaking of ranching and ecological damage, don't forget Lynn Jacobs' classic Waste of the West. Most of the text is now online, but finding an actual copy is well worth it to see the (often shocking) photo documentation of cattle grazing damage.

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ARE COWS JUST DOMESTIC BISON?

BEHAVIORAL AND HABITAT USE DIFFERENCES BETWEEN CATTLE AND BISON

George Wuerthner

Abstract: Due to gross similarities in size, food preference, and appearance, it is often asserted that bison and domestic cattle are ecological analogues. However, a review of their evolutionary history demonstrates that differences in evolutionary pressures manifest themselves in strikingly different modes of resource exploitation. Compared to domestic cattle, bison wander more, are less apt to regraze a site during a single growing season, will use steeper terrain, select and consume drier, rougher forage, and spend less time in riparian areas and wetlands. Due to a variety of factors, bison were unable to colonize vast portions of the West. Evidence suggests these major rangeland ecosystems evolved in the virtual absence of large herding animals. The introduction of domestic livestock into these areas has had particularly negative impacts upon these landscapes. This paper reviews the differences in habitat utilization and behavior that characterize cattle and bison, and the implications for management of western rangelands and preservation of native biodiversity.

Introduction

Bison (Bison bison) once ranged across much of North America from the eastern seaboard states to southeast Washington, eastern Oregon and northeastern California. They also roamed the high parks of the Colorado Rockies and occurred at higher elevations in the Northern Rockies in Glacier National Park, and the mountains surrounding Yellowstone (Meagher, 1973; McDonald, 1981; Reynolds et al. 1982). The greatest numbers were found on the shortgrass plains east of the Rocky Mountains that stretched from Alberta to Texas (Reynolds et al. 1982)--sometimes referred to as the "bison belt". Many plants in the "bison belt" have adopted flexible growth strategies that enable them to tolerate herbivory by bison, other ungulates, rodents such as prairie dogs and even invertebrates (Delting and Painter 1983, Painter et. al 1989).

Due to hide hunting, sport hunting and perhaps also as a consequence of the introduction of the horse which increased Native American hunting efficiency (Reynolds et al. 1982, Urness, 1989, Geist 1996), bison numbers plummeted nearly to the point of extinction by the late 1800's (Meagher, 1973). Domestic cattle have subsequently been substituted as the major large herbivore grazing most of the West.

As a consequence of gross similarities in shape, size, and foraging habits between bison and cattle, many have argued that cattle are merely filling the vacant niche left by the virtual extinction of bison.. Since bison herbivory was an important ecological influence upon many grassland ecosystems, many people assume that properly managed cattle have no negative impacts upon western rangelands, in part because they are thought to mimic bison herbivory pressures (Savory, 1983, Lauenroth et al. 1994, Goetz, 1994, Thomas, 1991) For example, in an article (Thomas, 1991) which appeared in Rangelands published by the Society for Range Management, the author states, "Long before the American pioneers laid eyes on the mountains and plains of North America, there were 'cattle' on our western ranges. Bison roamed the hills, migrating from winter to summer grazing areas, making seasonal use of these lands much as our domestic livestock do today. The bison and the domestic cow belong to the same family (Bovidae) and are genetically similar. They are also very similar in their grazing habits and preferences".

Some even assert that western rangelands, particularly the most arid landscapes, require disturbance impacts from domestic cattle to replace the impact it is claimed resulted from vast herds of bison, antelope or other wildlife in these areas. Thomas (1991) concludes that extirpation of the bison "would have put thousands of acres of rangeland into a stagnant and very unnatural situation except for one saving grace: we substituted domestic livestock for the buffalo." Others suggest that herding animals are necessary to break up soil crusts, trample seeds, remove "decadent" plant material, and are purported to increase rainwater penetration (Savory, 1983, 1989, USDA, 1989). The argument that cattle are ecological equivalents to bison is frequently used as an justification for continuing domestic livestock grazing on some public lands (Tohill and Dollerschell, 1990). So ingrained is the idea that livestock and grazing are synonymous that some livestock supporters assume removal of domestic cattle and sheep equal "no grazing" (Laycock, 1994) and caution against the presumed deleterious effects upon rangeland "health".

The absence of livestock is not the same as no grazing since most native rangelands experience a wide variety of herbivory pressures, from nematodes in the soil to invertebrates such as grasshoppers, to vertebrates such as prairie dog, antelope, elk and bison (Archer and Smeins, 1991). Under natural conditions, the populations of these native animals fluctuate seasonally and annually due to variation in predation pressure, competitive interactions between and within species, and availability of forage. Some have questioned whether the near constant numbers of cattle can be equated with naturally fluctuating numbers of wildlife (Heitschmidt, 1990). Others caution that plant response to herbivory is merely a defensive mechanism that should not be interpreted as a benefit or promoting rangeland "health", but rather as generalized plant responses to damage ( Belsky 1986, Belsky et al. 1993). Research reported by Geist (1996), Lott (1991), Norland (1984) and Van Vuren (1979) among others, suggest that the behavior and foraging strategies of bison are different than those found in domestic livestock, and as a consequence, it may be erroneous to equate the two with regard to herbivory pressure and other influences.

Evolutionary History

Bison (Bison bison) and cattle (Bos tarus) evolved from a common ancestor in Asia. This animal, Leptobos, appeared in the Pliocene, and became widely distributed throughout Eurasia. Both Bison and Bos branched from Leptobos prior to its extinction in the late Pleistocene. Early in their evolutionary history, bison resembled cattle in many features including horns that pointed forward, a straight back and few secondary sexual characteristics. Early forms of both cattle and bison inhabited woodlands and forested areas. During the Pleistocene, bison gradually adapted to exploit the steppe tundra ecosystem and eventually spread into the available habitat across Asia and Europe (McDonald, 1981, Geist 1996).

Bison colonized North America via the Bering land bridge during the early to middle Pleistocene (Guthrie, 1980). Bison evolutionary history in North America is complex and interpretation of the finer points has been controversial, but the form we now recognize as Bison bison reached maximum range and density approximately 2,500 BP (Guthrie, 1980; McDonald, 1981).

Although bison became an inhabitant of open landscapes such as plains, and grassy savannas, most of the evolutionary precursors of domestic cattle were inhabitants of subtropical lowland regions where they inhabited swampy, humid forests. Bison are the only members of the entire Bovini line that do not have at least a partial tropical distribution (McDonald, 1981). Today, several species of wild cattle are confined to southeast and central Asia where they graze or browse open areas in rainforests and uplands (McDonald, 1981). Their niche is similar to that of whitetail deer in North America, an animal that favors the edges along forest borders and the lush cover of riparian and other shrubby vegetation.

Residual herds of bison are still found in Eurasia where they are restricted to forest and mountain areas. However, these animals are said to resemble cattle in appearance and behavior (Guthrie, 1980). In North America, bison occupy primarily grasslands or parklands and have evolved into an animal adapted to open landscapes, exhibit migratory behavior, and tolerate arid environments and a shifting mosaic of resources (Renyolds et al. 1982, Geist 1996).

During the Pleistocene, vegetation in much of North America changed substantially. Broadleaf evergreen species were replaced with a greater abundance of coniferous species, resulting in a deterioration in herbivore forage opportunities. However, at the same time, there was an expansion of steppe areas with fibrous and abrasive foods (McDonald, 1981, Geist 1996). The adaptive response of bison was to increase body size and expand their ruminant digestive system to process large amounts of low quality forage (McDonald, 1981).

In woodlands where food resources are patchy, small isolated groups of animals are all that can be supported within any parcel of the landscape. Living in small groups or in isolation increases vulnerability to predation. Larger body size can discourage predators, and not surprisingly, early forms of bison that lived in forested landscapes tended to be larger. However, larger size results in a slower maturation process, with animals living longer but producing fewer young. Social behavior is less highly developed (Geist, 1971), as well.

Evolution of Bison bison in a grassland regime, favored an animal with small body size (compared to woodland and earlier glacial versions of bison. A high degree of social behavior that manifests itself in strong herding characteristics, high biotic potential and rapid maturation rates (Geist 1996). The modern day bison evolved to its present form only 5,000 years ago (Hudson and Frank 1987). Guthrie (1980) summarizes the basic characteristics expected of animals evolving under different habitats. Savanna-steppe adaptations include non-lethal fighting apparatus, large groups, class hierarchy, elaborate social organs, migratory-nomadic behavior, less selective feeding and the ability to digest coarse fiber. By contrast, species evolving in woodlands tend to display the following adaptations: lethal fighting apparatus, small groups, linear or modified linear hierarchy, territorial fidelity, selective feeding strategies and reduced seasonal adaptations. A comparison between cattle and bison clearly shows that American bison fit the savanna-steppe adaptations while cattle, despite centuries of domestication and breeding, are defined more by the woodland attributes.

Morphological adaptations of the bison to facilitate existence in a grassland environment include the downward rotation of the head relative to the vertebral column, along with the lateral placement of the eye orbits which permits maintenance of visual contact with the herd as well as predator detection while grazing. Short limbs also permit easier access to short grasses (McDonald, 1981). Cattle lack the well-developed features of bison that are adaptations to short grass plains environments, including the downward rotation of the head relative to the vertebral column. Plus, cattle tend to have longer legs (this varies among breeds), and a straight back which may permit short term burst of speed, but are not useful for long distance movement. Not only are cattle less mobile by nature, domestic breeding programs have resulted in animals that are less fit for long distance movement.

Bison tend to have aggressive encounters that are ritualistic rather than lethal. Bison horns have rotated towards the side of the head where they are less effective as lethal weapons (Guthrie, 1980). Most aggressive encounters involve head shoving, with encounters typically decided by threats (Meagher, 1973, Geist 1996). During the rut, bull bison develop exaggerated hair tuffs on the head and front legs that are used to display size and social rank. They lose these features outside of the rut, taking on the gross features of females. This defuses antagonism between bulls outside of the rutting season and is an adaptation to herding that permits living together in open spaces. (Geist, 1971, 1996; Guthrie, 1980; McDonald, 1981)

Another adaptation to open prairie landscapes is sustained flight from predators (Geist 1996). Adaptations bison possess for sustained running include muscular front quarters and small hind quarters with light boned legs that are energy efficient to lift and move. In addition, the bison's hump acts as a fulcrum that permits the hind legs to be swing forward to maintain sustained speed over long distances (Geist 1996). According to Guthrie (1980) this rotation of forequarters, with the shoulders functioning as a fulcrum permitted a cantering gait--a rolling, energy efficient movement. Guthrie theorizes this was an adaptation to frequent long distance movements, in which wild bison seek areas with adequate forage, attempt to capture phenological peaks in plant growth, or obtain water. Geist (1996 ) attributes predation avoidance as the major influence on development of this running gait. Which ever theory is correct, bison are adapted to cater efficiently and over long distances with relatively little energy cost.

The large size of bison is an effective defense against predation by most carnivores. Recent studies of the relationships between wolves and bison have shown that calves and older adults make up the majority of prey for wolves, while healthy adults are relatively safe from attack (Carbyn, et. al. 1993). Furthermore, where wolves have a choice of alternative smaller prey such as elk or deer, bison are seldom preyed upon.

Bison move frequently, shifting habitat use suddenly. Such sudden movements were noted by many early travelers on the plains. For instance, John Kirk Townsend (1978) traveling along Wyoming's North Platte River in 1834 commented that "buffalo still continue immensely numerous in every direction, and our men kill great numbers...". But the next day he wrote, "When we rose this morning, not a single buffalo, of the many thousands that yesterday strewed the plain, was to be seen. It seemed like magic. Where could they have gone? I asked myself this question again and again, but in vain."

More recently many studies have documented the tendency for bison to move extensive distances compared to cattle. Van Vuren (1979, 1983 noted that bison) in the Henry's Mountains of Utah seldom stayed in one location more than 3 days. Even where habitat variation is low, bison seem to wander widely. Lott and Minta (1983) characterized bison as "highly mobile" animals. According to Lott (1991) free roaming bison introduced to Catalina Island in California had much larger home ranges than nearly all species of African ungulates, except during migration periods. For example, water buffalo which are approximately the same size as American bison, have home ranges about 5% as large as the bison on Catalina Island, even in drought periods (Lott, 1991). Carbyn and his colleagues (Carbyn et al. 1993) commented that wood bison in Canada often moved up to 32 km over a short period of time "for no apparent reason". Norland, (1984) studying bison in Theodore Roosevelt National Park, noted that animals seldom stayed in the same location for more than 48 hours and characterized them as being "highly mobile, moving to new localities and habitats almost daily." Norland concluded that due to the constant movement and random nature of these movements that plants were "potentially grazed only once, if at all, in a 3-4 week period". Meagher (1989) noted that though bison may have a strong fidelity to a home territory, they do make sudden movements of considerable distance.

Not only do bison move more frequently than cattle, but their selection of habitat within the landscape is also different. Van Vuren (1979, 1983) reported that an introduced herd of wild bison in Utah's Henry Mountains differed from cattle using the same ranges in several notable ways. Bison tended to stray further from water sources, used steeper terrain and higher elevations than cattle. In northern Colorado, Peden et.al. (1974) found that bison spent less time near water and only watered once a day. Similarly, Norland (1984) reported that bison would go to water once a day. The length of stay at watering areas was "short duration--one hour or less for even the largest herds". In both studies it was noted that bison appeared to prefer drier forage, spent less time in swales and depressions where soil moisture was higher than might be expected. Peden (1974) also noted that bison selected rougher, less digestible forage, giving them a competitive advantage on native grasslands where forage quality varies seasonally. The ability to utilize lower quality forage also results in better distribution of grazing pressure on rangelands grazed by bison than under livestock usage.

Cattle are less efficient water users than bison, and display a marked preference for moister forage. Pinchak and colleagues (Pinchak et al. 1991) reported that 77% of the observations of cattle grazing foothill ranges in Wyoming were within 366 meters of water and noted that the majority use was on wetlands or subirrigated, level sites. Similarly, Smith (1992) found that cattle selected a higher percentage of floodplain habitat and a lower percentage of upland habitat than these habitat types represented in their study area, as did Goodman (Goodman et. al. 1989). The negative effects of domestic cattle on riparian ecosystems are well documented (GAO, 1988, Kauffman, and Krueger, 1984) as is the ecological value of riparian areas to wildlife (Chaney, et al. 1990; GAO, 1988; Beschta, et al. 1991). Riparian areas make up approximately 1% of the land area of the West, yet 60-80% of the native vertebrate species rely upon this habitat for their continued survival (GAO, 1988; Chaney, et. al. 1990).

Because of their propensity to linger in riparian areas or wetlands, domestic cattle pose a far greater threat to arid land biodiversity than native species like bison. Preventing damage by livestock to riparian areas requires capital investments in upland water development, fencing, salting, and herding--all of which increase the costs per unit of production, quickly exceeding the financial return on investment in many arid western rangelands, unless costs are subsidized (Holechek, 1992).

Furthermore, bison are able to forage in deep snow (Meagher, 1973, Carbyn et.al. 1993) which at least in northern regions is a distinct advantage over domestic livestock which require supplemental feed. Bison also have a hide of higher insulative value than cattle (Peters and Slen, 1964), another adaptation to harsh winters and seasonal food limitations.

One more difference between domestic cattle and bison may be habitat utilization. Bison bulls make up a higher proportion of the herd than bulls in a typical cow-calf operation or other livestock operations. Geist (1996) has pointed out that competition for forage is keen, and differences in bison foraging behavior based upon the sex of the animal results. Bison bull compromise security in favor of food, while cows and calves compromise food in favor of security. Males are more likely to wander further to find isolated patches of high quality forage. As a consequence, a herd of wild bison would likely graze a landscape more uniformly than if the same area were grazed by a herd of domestic cattle. Bison

naturally wander widely, far more than cattle, even under essentially open range conditions (Pinchak et. al. 1991).

Although there are historical accounts sometimes documenting heavy grazing by bison, it would be incorrect to assume that bison carpeted the plains as one great mowing machine. Many early travelers on the plains noted both the abundance and the absence of bison and other large ungulates due to seasonal movements and other factors. For example, in 1806 while returning from the Pacific, Captain Clark (1964) of the Lewis and Clark Expedition traversed nearly 200 miles of Montana from the Continental Divide in the Big Hole Valley near the Idaho border, down to the Missouri headwaters confluence, across the Gallatin Valley and down the Upper Yellowstone to where the town of Big Timber, Montana now sits before they found and killed a single bison. Their Indian guide, Sacajawea, informed Clark that the bison were once numerous in the Upper Missouri headwaters but had been driven away by heavy Indian hunting. Nevertheless, further down the Yellowstone below what is now Billings, Montana, Clark (1964) noted "the entire country is enlivened by herds of buffalo, elk and wolves." And in 1834, John Kirk Townsend (1978) crossing the region near South Pass, Wyoming complained that his party was suffering from a what of food, commenting that "buffalo are rarely seen." Thus the shifting mosaic of grazing pressure resulting from near constant movement, along with periodic population decline due to variability in climatic condition almost ensured that heavily grazed areas would be rested, often for months or even years. Such lengthy rest is seldom emulated by most livestock management schemes which tend to focus on maintaining constant numbers with at most a reprise of a year or two from grazing influences.

Finally, bison interact with other native species in ways not typically observed with domestic livestock, that may result in reciprocal ecological relationships between different native species. For example, it was noted that bison tended to graze areas around prairie dog towns, thus enjoying succulent new regrowth of plants previously cropped by prairie dogs while at the same time reducing the grass cover which benefited the rodents by making it easier to spot predators (Coppock et. al. 1983). The factors listed above explain some of the differences between cattle and bison utilization of the landscape.

Historic Anomalies in Bison Distribution

A large portion of the West, particularly the majority of public rangelands that are located in the Intermountain West and Southwest consist of ecosystems that historically did not support large herds of bison, if at all. These include most of the sagebrush steppe of the Intermountain West, the Southwest desert regions and the palouse grasslands of Washington and eastern Idaho (Miller et al. 1994; Mack and Thompson, 1982).

A number of researchers have commented upon the historic scarcity of bison in the sagebrush-steppe zone west of South Pass, Wyoming and total absence from the Great Basin Sagebrush deserts. When the first Europeans entered the western United States during the fur trade era in the early 1800's, bison were reported in southeast Idaho (Work, 1913, Russell, 1955), northern Utah, and eastern Oregon (Ogden, 1910, Bailey, 1936). However, they were absent from many other portions of the Intermountain West such as the Great Basin Sagebrush deserts of Nevada, the desert grasslands of Arizona and elsewhere west of the Rockies (Reynolds et. al. 1982). Other large ungulates such as elk, deer, antelope, and bighorn sheep were also unevenly distributed over large areas of these semi-desert and desert regions, with bighorn sheep and antelope being the most numerous large animals (Davis, 1982; Ogden, 1910; Simpson, 1983).

There is evidence suggesting that even where bison were found west of the plains, their numbers were small, and distribution was patchy. Periods of favorable climatic and forage conditions probably enabled intermittent recolonization of suitable habitat by herds moving in from the plains. However, deformities among the skulls and teeth of bison remains from eastern Oregon suggest such periodic recolonizations were infrequent and that these animals were isolated, and locally inbred populations (McDonald, 1981). Daubenmire (1985) argued that protein deficiencies of native bunchgrass rangelands, along with occasional deep snow limited bison populations along their western margins--although as seen earlier, bison are more efficient at extracting nutrients from forage than other ruminants (Peden et al. 1974)

Mack and Thompson (1982) suggested that grass phenology may have limited bison productivity compared to the plains. While cool season grasses provide plenty of protein early in the spring, early onset of dormancy in summer, with a consequent loss of nutritive value, may have stressed lactating female bison. On the plains, a mixture of cool season and warm season grasses extends the availability of nutritious forage.

Van Vuren (1987) has postulated that on rangelands in the Intermountain West forage was inadequate to sustain large numbers of bison except in a few locations. Frequent local extinctions due to weather, hunting by humans, combined with the low productivity and slow recolonization rates may have kept bison numbers exceedingly low over this region and may account for the relatively limited distribution.

Further evidence for the absence or limited distribution of bison throughout the Intermountain West comes from the native vegetation itself which is not adapted to persistent, heavy grazing (Mack and Thompson, 1982). Vegetation on the Great Plains was dominated by blue grama (Bueteloua gracilis) and buffalo grass (Buchloe dactyloides) which seem to tolerate grazing. The native vegetation in the Intermountain West is dominated by species such as bluebunch wheatgrass (Agropyron spicatum), Idaho fescue (Festuca idahoensis), and Indian ricegrass (Oryzopsis hymenodies), which are caespitose or bunchgrasses, and thus less tolerant of both grazing and trampling (Mack and Thompson, 1982, Mack, 1986).

Conclusions

Due to their respective evolutionary histories, a variety of behavioral, biological and ecological differences exist between bison and cattle. Cattle are poorly adapted for a semi-arid landscape with rugged terrain, and cattle grazing may lead to degraded rangelands . Wild free-roaming bison, on the other hand, are better adapted to their environment, and were sustained for thousands of years without contributing to serious widespread degradation of rangeland ecosystems.

Since substantial differences in behavior and habitat use and selection exist between bison and cattle, it is inaccurate to suggest that cattle fill the ecological niche left by the extirpation of the bison. Rather, cattle should be viewed as a new ecological force that differs significantly from the native species.

Furthermore, some native ecosystems apparently did not support bison in any numbers or they were completely absent. In particular, much of the Great Basin, Palouse Prairie, Southwest deserts, and California annual grasslands evolved without the presence of bison. These native rangeland ecosystems display limited tolerance to grazing pressure of any kind (Jones et. al 1991; Miller et al, 1994).

The assumption that exotic animals are a replacement for native species should be scrutinized closely. Gross outward similarities often do not translate into similar use of the landscape.

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