In the early days of the cattle range, before sound land management of the plains was understood, cattlemen were perplexed to witness mushrooming populations of prairie dogs. Formerly lush grassland often became a dog town “wasteland” following the introduction of cattle. Believing that the prairie dog, and not the cattle, was responsible for this sudden transformation, ranchers rapidly came to despise prairie dogs. A massive war of extermination began against these “varmits” that “ate the grass down to nothing.” In reality, the appearance of prairie dogs merely indicated that the land was being overgrazed. As the bison had done before them, cattle now began to open up to the prairie dogs new territories that they could not otherwise colonize. Prairie dogs were never found on the eastern prairies simply because they could not contend with the taller growth of the more humid grasslands.
On their own, prairie dogs cannot easily invade unbroken areas of established grassland. The grass cover simply rejuvenates faster than the animals can work. But if the land has been disturbed by overgrazing, prairie dogs can quickly spread. Once established in an area, the animals wage a constant struggle against the vegetation. Since tall-growing plants offer concealment to a predator, the plants are routinely clipped off even if they are not to be eaten.
The feeding, clearing, and burrowing activities of the dog town tend to retard the grasses while encouraging the persistence of forbs—the broadleaf plants that quickly invade disturbed ground but are eventually crowded out by the returning grasses. By arresting the normal process of plant succession, an active dog town delays the return of the site to its climax vegetation of grasses. In so doing, it inadvertently perpetuates a wider variety of plants than would otherwise be found on the site.
Selective feeders, prairie dogs put pressure on a particular plant species when it becomes most abundant, then ignore it almost entirely in favor of another, and so on. This cyclic feeding allows each species to recover, preventing it from being eliminated.
Dry years help the prairie dog maintain control over the vegetation, and thus favor town expansion, while wet years speed recovery of the grasses and work against the town. Towns that had spread into lush grassland during the favorable conditions of drought may be severely reduced or even eliminated with the return of adequate precipitation.
In some cases, the clearing activities of prairie dogs may actually speed plant succession. As a direct result of overgrazing by domestic stock, much of the grassland of the semi-arid West was invaded by sagebrush, a tough, drought-resistant plant that tends to perpetuate itself indefinitely once introduced. By cutting down the sage, prairie dogs eliminate it from the plant community and open the land to grasses.
In its struggle for control of territory, the prairie dog was aided by the bison. The vast herds that moved across the landscape like a black plague of giant locusts left choice tracts of the grasslands devastated in their wake. The effects of such a physical force are difficult for us to comprehend today. Migrating northward in huge columns that sometimes measured 80 kilometers (50 miles) across, the bison cropped and trampled the greening spring grasses. Surely when the bison and the prairie dog were finally replaced by cattle, the grasslands, free at last from such punishment, would flourish. But no, instead the grasses languished. How could this be so?
Nature is always more complex than our perception of it. For countless centuries the Great Plains had survived its many moods of drought, dust storm, and wildfire, its scattered plagues of bison and grasshopper. Nature knows no “varmits,” and change is not catastrophe, but opportunity. But to the settler who shot hawks, owls, and eagles to protect his calves, poultry, and children, the lesson was a long time dawning.
Ironically, the grasslands needed the periodic despoilment of bison and burrow. When the bison herd moved on, it left behind tons of fertilizer, key to the area’s future rejuvenation. But the millions of hoofs also left the ground compacted. Were it not for the ceaseless activities of countless burrowing animals, including the industrious prairie dogs, loosening the soil and undoing the damage, the bison would have eventually destroyed much of their range.
For an animal so successfully adapted to life on the unrelieved expanses of the open plains, it is ironic that today prairie dogs survive in isolated colonies at the very margins of its desirable habitat.