The National Park Service (2015) describes that wildfires, while normally seen as destructive forces, are actually critical to maintaining grasslands. They suppress shrubs and woody plants from proliferating, which ensures that it remains a grassland and not a forest. Fires also enable the re-seeding of native grasses. The main source of fire ignition without human intervention is lightning, but the practice of burning harkens back to Native Americans in pre-colonial times. Even bison prefer grazing from recently burned areas (National Park Service, 2015).

Grasslands are able to withstand fires because of where their apical meristems are, or the point from which they grow. “In grasses, these points are located beneath the soil surface. This unique adaptation protects them from disturbances that destroy or seriously damage other plants” (Ducks Unlimited, n.d.).

According to a paper by VanAuken (2009), forests encroach on grasslands for a variety of reasons. In the case of overgrazing, herbivory is chief among these causes, which decreases the occurrence of fires. However, a more recent study informs that herbivores also increase plant diversity by assisting with seed dispersal, creating space for understory growth, and increasing ground-level light, which prevents competitive exclusion especially in productive grassland systems. (Borer, 2014)

As described by the Wildlife Conservation Society (n.d.), approximately 30 million bison used to populate the Great Plains. They played a central role in shaping the grassland ecosystems: their grazing behavior affected fire occurrences, created a diversity of habitats, and supported the lives of many endemic insects, reptiles, amphibians, birds, and mammal species. Importantly, they helped prevent the spread of invasive trees. Their wallowing behavior created depressions in the ground that held water for use by wolves and grizzly bears. The Wildlife Conservation Society has been instrumental in re-introducing bison back to their native ranges, but cattle grazing has also been proposed as an alternative.

To introduce cattle grazing as a replacement to bison, however, there must be control. Aside from overgrazing, in the past, lack of control has caused boom-and-busts in livestock populations, which has affected this biome. “Livestock rebound following bad winters and large die-offs to again overgraze rangelands, reduce forage supplies, and increase the potential for future disasters.” (Reading et al., 2010). One way ensure sustainable grazing is to alternate grazing land. Allocating land for non-grazing during seasons of growth allows forage plants to rest and encourages seed production among forage species.

References

National Park Service (2015). Grassland Fire Ecology: Resource Brief. U.S. Department of the Interior. Retrieved from: https://www.nps.gov/rlc/crown/upload/Grassland-Fire-Ecology-Brief.pdf

Ducks Unlimited (n.d.) Grazing and Fire. Retrieved from: https://www.ducks.org/conservation/waterfowl-habitat/biodiversity-in-the-grassland-biome/grazing-and-fire?poe=related

Van Auken, O.W. (2009). Causes and Consequences of Woody Plant Encroachment into Western North American Grasslands. Journal of Environmental Management 90.

Borer, E. (2014). Herbivores and nutrients control grassland plant plant diversity via light limitation. Nature Publishing Group. Retrieved from: https://www.nature.com/articles/nature13144

Wildlife Conservation Society (n.d.) Bison. WCS North America. Retrieved from: https://northamerica.wcs.org/Wildlife/Bison.aspx

Reading, R., Bedunah, D., Amgalanbaatar, S. (2010). Conserving Mongolia’s grasslands with challenges, opportunities, and lessons for America’s Great Plains. Great Plains Research. 20. 85-108.

Featured Photo: © Chris Helzer at The Nature Conservancy