Wednesday, October 8, 2008

Ranching Myths: Cattle Have Replaced Bison


Cattle Have Replaced the Bison


Although cattle and bison have a common evolutionary ancestor, so do the polar bear and black bear. Yet we would not suggest that these two bears can inhabit the same type of landscape or that they are ecological analogues of one another. Cattle evolved in moist Eurasian woodlands and are poorly adapted to arid regions. In comparison with bison, cattle use more water, spend more time in riparian areas, and are less mobile. They are poorly adapted to dry western rangelands-one reason why livestock grazing has been so detrimental to these ecosystems.

Bison feed in one place for a few days, then move on, whereas cattle tend to "camp out" in the same location for weeks, overgrazing the landscape in the process. Bison survive on available, native forage. Cattle require extra feed to survive northern winters, which typically means hay production and accompanying dewatering of streams. Cattle are poorly adapted to dealing with predators, being rather slow and unintelligent. Bison retain their wild instincts for avoiding and fending off wolves, grizzlies, and other carnivores.

Wild bison functioned within ecosystems in ways that livestock do not. Their bodies served as food for predators and were scavenged by ravens, coyotes, and magpies. What was left of their carcasses decomposed and was returned to the soil. Bison were a part of, and contributed to, a great diversity of life. Livestock, on the other hand, represent a large net loss of energy and biomass to an ecosystem, as their bodies are removed for human consumption elsewhere.

Despite the simplistic claim that cows merely replace bison, it's not just bison that have been replaced by this exotic, domesticated species. On most rangelands today, cattle are the only major herbivore. Yet in the days before livestock, an entire suite of species fed on the grassland plants, from grasshoppers and sage grouse to prairie dogs and pronghorn. Substituting a single species-with different dietary preferences-for this diverse group of herbivores results in overuse of some plant species and grants competitive advantage to others. These other plants are often invasive and less palatable to many native herbivores.

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