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The Carletonian

The Carletonian

Arb Notes: Cows Put the Bite on Invasives

<enowned Northfield fact is that it is also home to a large bovine population. Why should we be so proud of Northfield’s tremendous bovinity? It turns out that cows might provide myriad ecological benefits to native tallgrass prairies – one of the most fragmented and least protected habitat types in the world.

To many skeptics, cattle grazing seems like a counterintuitive solution to the problems that face tallgrass prairie plants: declining seed set, species richness, and genetic integrity. Historically, however, prairies evolved to thrive on ecological disruptions such as frequent fires and bison grazing. One of the main benefits of grazing is the creation of areas of short grass, which increases the structural heterogeneity of the landscape. These patches of short grass provide valuable habitat for animals such as prairie chickens and  ground squirrels.  Observations indicate that dominant tall grasses are highly susceptible to cattle grazing. If this is true, then a reduction in the density of tall grasses would increase total species richness by giving shorter grasses a chance to take root. A study conducted by Carleton students and faculty in the Arboretum found that cattle grazing may increase reproductive success in some plant species, although not all results were positive.

The Minnesota Department of Natural Resources is not yet sold on benefits of bovines in conservation. In a talk given recently at the Minnesota Native Plant Society, Carleton alum Dr. Fred Harris ’80 pointed out that in terms of grazing habits, bison are very different from cattle. One of the main concerns surrounding “conservation grazing” is that cows (unlike bison) tend to congregate in wetter areas. Disruptive hoof-action turns up wet soils, creating denuded zones devoid of plant life. Long-lived rare prairie plants can take up to 10 years to fully recover from disruption by cattle. Thus, while grazing offers a variety of short-term benefits, long-term ecosystem-wide effects are less certain.

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