Effects of Grazing versus Fire for Prairie Management

Minnesota’s tallgrass prairies depend on disturbance (e.g., fire, grazing, drought), without which they would rapidly transition to woodland and forest. Land managers often use prescribed fire and “conservation grazing” (the use of grazing by domestic animals to achieve conservation goals) to preserve prairie plant communities and the many pollinators, birds, and mammals that depend on them. Effects of fire on northern tallgrass prairies are well documented. Prescribed burns can have unintended consequences for insect communities. Prairie dependent butterfly species that overwinter above ground in a life stage with little to no mobility may be particularly vulnerable to fire (Panzer 2002; Thom et al. 2015), especially if there are few local refugia from which insects may recolonize a burned site (Swengel 1998; Driscoll et al. 2010). Stemnesting bees are similarly likely to be negatively impacted by fire (Tooker and Hanks 2004). For these reasons, and because prescribed fires are expensive, require significant personnel numbers and time, and can only be completed during specific windows of time, many managers have turned to conservation grazing as an attractive alternative. We know far less about the effects of grazing on prairie dependent bees and butterflies in Minnesota tallgrass prairies.

The goal of our study is to address this knowledge gap by examining the direct and indirect effects of fire vs. grazing management on vegetation and pollinator diversity and abundance in Minnesota tallgrass remnant prairie.

For more information on this project, please contact the researchers directly. Diane Larson: dlarson@usgs.gov; Jen Larson: jllarson@umn.edu; Julia Leone: leone050@umn.edu; Patrick Pennarola: penna041@umn.edu.

Project funded by the Environment and Natural Resources Trust Fund.


(Above) Patrick Pennarola, a MS student in the Entomology Department at the University of Minnesota, leads a group of workshop participants to collect pan traps as part of a bee monitoring methods exercise at Overby WPA (USFWS, Pope County, MN). Photo by Diane Larson.

Julia Leone, a PhD student in the Conservation Sciences Department at the University of Minnesota, leads a group of workshop participants in a butterfly monitoring methods demonstration at Overby WPA (USFWS, Pope County). Photo credit Jen Larson, UMN.

The remaining remnant prairies are home to many conservative species, such as this white lady’s slipper (Cypripedium candidum) at Rothsay WMA (Wilkin County, MN). Conservative species are those that most require native prairie habitat to survive. Rothsay WMA contained a prairie remnant managed by burning only. Photo credit Jen Larson, UMN.

A pair of mating Arctic skipper (Carterocephalus palaemon) butterflies on orchardgrass (Dactylis glomerata) at Ben Wade WPA in Pope County, MN. While Arctic skippers are not a rare species, several members of the same subfamily of butterflies are listed as threatened or endangered, including the Dakota skipper (Hesperia dacotae) and Poweshiek skipperling (Oarisma poweshiek). These and other members of the subfamily Hesperiinae of butterflies require prairie to exist. Photo credit Julia Leone.

At Overby WPA (USFWS, Pope County, MN), local cattle owners contract with USFWS to graze federal lands. This grazing provides necessary disturbance to prevent woody encroachment from trees and shrubs, and maintain prairie habitat. Photo credit: Jen Larson, UMN.

Project Photos

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