The interaction of two disturbances—bison grazing patterns and fire—increases biodiversity by creating a heterogeneous patchwork of plant communities in grasslands.

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The Great Plains are a huge expanse of grassland located west of the Mississippi River and east of the Rocky Mountains in the United States and Canada. Millions of bison used to roam the tallgrass prairies that once covered the Great Plains, grazing in patches as they went. Fires caused by lightning or set intentionally by native peoples to renew the grasslands were also common. The relationship between fire and grazing patterns had a big impact on how plant communities developed in the tallgrass prairie.

Fires are important to biodiversity, because bison prefer to graze patches of grassland that have been burned recently. Bison grazing patterns also influence the size and intensity of fires. The interactions between these two different types of disturbances— fires and grazing patterns—helps create a heterogenous, or mixed, patchwork of plant communities. For example, these interactions lead to different plant heights, density, and mixtures of species. This helps support more biodiversity in tallgrass prairie ecosystems.

Scientists think of biodiversity on three levels—genetic diversity (different genes and combinations within a species), species diversity (the number of different species within an ecosystem), and ecosystem diversity (how many different ecosystems are found in a region). Biodiversity helps organisms adapt to environmental changes, maintain food webs, and provide services that life depends on, such as water retention and waste decomposition.

Today, most of the land that made up the Great Plains is managed as rangeland for cattle production. Land managers usually only manage the number of cattle and where and when they are grazing on the land. Fire is rarely used anymore as a way to manage cattle grazing. Instead, intensive rotational grazing approaches, where animals are moved rapidly between heavily grazed plots, have become more popular as a management approach. This style of grazing allows the plants that the cattle most like to eat to recover between grazing sessions. However, it does not produce the patchwork of plants that leads to greater biodiversity. 

The Nature Conservancy has successfully used fires and continual cattle grazing to manage its Tallgrass Prairie Preserve in Oklahoma. This approach helps to promote biological diversity and increases agricultural productivity, and can help  support native plant and animal species. There is even some evidence that this approach, where appropriate, could reduce the need for protein supplements in cattle during winter months. This would lead to lower management costs.

This Oklahoma State University video takes viewers on a tour of TNC’s Tallgrass Prairie Preserve and talks about the impact of fire, grazing, and drought on the ecosystem:

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“The interaction of grazing and fire is an important influence on diversity and spatial patterns of vegetation in mesic Great Plains grasslands (Biondini et al. 1989, Vinton et al. 1993, Steuter et al. 1995, Hartnett et al. 1996). Fire influences bison grazing patterns, and bison grazing determines the extent and intensity of fires. Bison prefer recently burned areas because of the high-quality regrowth after a fire (Coppedge and Shaw 1998). When only a portion of the area available to bison is burned, intense grazing of burned patches postpones grazing on unburned patches (Figure 4), which results in an accumulation of fuel and an increased probability of fire in unburned patches (Steuter 1986, Hobbs et al. 1991). This interactive model is complicated by the season in which a burn occurs, which influences the effects of fire (Ewing and Engle 1988, Biondini et al. 1989, Howe 1994a) and bison preferences for certain patches (Shaw and Carter 1990, Coppedge and Shaw 1998). Thus, the interaction of these two disturbances—fire and bison grazing patterns—is capable of producing a dynamic patch mosaic of plant communities within grazed grasslands (Steuter et al. 1995, Hamilton 1996).” (Fuhlendorf and Engle 2001:628)

Journal article
Restoring heterogeneity on rangelands: ecosystem management based on evolutionary grazing patternsBioScience, Vol 51, Issue 8Fuhlendorf, SD; Engle, DM

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