Editor’s note: a shorter version of this story appeared in the October/November 2024 issue of Arboretum Magazine.
Have you ever experienced a jolt of concern on a visit to the Arboretum after spotting smoke and flames rising from the Bennett-Johnson Prairie? While this sight might be alarming to visitors, it’s actually part of a carefully calculated management plan for the Arboretum’s natural areas.
Prescribed fire, sometimes referred to as a prescribed or controlled burn, is a management strategy commonly used to restore and maintain prairie ecosystems. Prior to European settlement, fire disturbance occurred over thousands of years and prairies evolved under conditions of periodic fire.[1] At the Arboretum, horticulturists focused on natural resources use prescribed fire as a tool to mimic this disturbance to benefit native species while suppressing undesired invasive or non-native species based on the time of year.[3]
Prescribed fire conducted in the fall can encourage the growth of forb species such as prairie clover, blazing stars, asters or coneflower.[6] In contrast, a spring fire can help suppress non-native cool-season grasses such as smooth brome or Kentucky bluegrass and reduce tree and shrub density. Spring fires also encourage the growth of native warm-season grasses including big bluestem, switchgrass and sideoats grama.[5] Last year, more than 25 acres were burned in the Prairie and Spring Peeper Meadow in the fall.
Natural resources horticulture staff Jake Lavigne (left) and Annie Gunness work together as a team, lighting a head fire and then putting out fire along the fire break using a water pump to cool hot areas after fire has passed.
Although prescribed fire can benefit native vegetation and suppress invasive species, the practice may also have unintended consequences for wildlife, including invertebrates, if not conducted properly. When prescribed fire is implemented after May, larvae of invertebrates, including the Minnesota state-threatened regal fritillary butterfly (Speyeria idalia), have high mortality rates in prescribed burn units.[4] Overall, local populations of invertebrates may not survive repeated prescribed burns, particularly if the frequency of the burn is too high (every one to two years), or if sections of the prairie are not left unburned.[8][4]
For butterfly species such as the regal fritillary, as well as other invertebrates, a duff layer is necessary for overwintering. Burning only fractions of the entire prairie at a time is necessary for the survivability of this invertebrate and others, and the cadence of burning matters too.
Averaging three to four years between burns at a minimum will aid in the succession of this species in a tallgrass prairie while still providing benefits to native vegetation and invasive species suppression.[2] Best management practices for prescribed fire include conducting a pre-burn survey for rare bumble bees, butterflies and other target wildlife species; burning no more than one-third of habitat in a given cycle; burning based on project goals; mowing fire breaks to create patches of unburned areas; and mapping the extent of each fire for proper record keeping.[7]
Learn more about the Arboretum’s natural areas, including the Prairie, on the Arboretum’s Natural Areas page.
Annie Gunness works as a Natural Resources Horticulturist at the University of Minnesota Landscape Arboretum and has been with the Natural Lands Team since 2017. She manages restoration efforts within maple-basswood forests, oak savanna, tallgrass prairie and wet prairie habitat including the iconic Bennett-Johnson Prairie. She also manages the display gardens representing these ecosystems such as the Grace B. Dayton Wildflower Garden, Prairie Demonstration Garden and Joanna Frerichs Garden for Wildlife. Annie earned a M.S. degree in Natural Resources Science and Management from the University of Minnesota where her graduate research focused on tradeoffs for birdsfoot trefoil management in tallgrass prairie restoration.
References
1. Anderson, R.C. (2006). Evolution and origin of the Central Grassland of North America: climate, fire, and mammalian grazers. Journal of the Torrey Botanical Society, 133(4), 626–647. https://doi.org/10.3159/1095-5674(2006)133[626:EAOOTC]2.0.CO;2
2. Caven, A. J., King, K. C., Wiese, J. D., & Brinley Buckley, E. M. (2017). A descriptive analysis of Regal Fritillary (Speyeria idalia) habitat utilizing biological monitoring data along the big bend of the Platte River, NE. Journal of Insect Conservation, 21(2), 183–205.https://doi.org/10.1007/s10841-017-9968-0
3. Eisenberg, C., Anderson, C. L., Collingwood, A., Sissons, R., Dunn, C. J., Meigs, G. W., Hibbs, D. E., Murphy, S., Kuiper, S. D., SpearChief-Morris, J., Little Bear, L., Johnston, B., & Edson, C. B. (2019). Out of the Ashes: Ecological Resilience to Extreme Wildfire, Prescribed Burns, and Indigenous Burning in Ecosystems. Frontiers in Ecology and Evolution, 7.https://doi.org/10.3389/fevo.2019.00436
4. Huebschman, J.J., & Bragg, T.B. (1999). Response of regal fritillary (Speyeria idalia Drury) to spring burning in an eastern Nebraska tallgrass prairie, USA. Natural Areas Journal, 20(4), 386–388.
5. Pavlovic, N. B., Leicht-Young, S. A., & Grundel, R. (2010). Short-term effects of burn season on flowering phenology of savanna plants. Plant Ecology, 212(4), 611–625. https://doi.org/10.1007/s11258-010-9851-5
6. Roberton, B., & Rebar, D. (2022). Timing of prescribed burns impacts plant diversity but not investment in pollinator recruitment in a tallgrass prairie. Ecosphere, 13(1). https://doi.org/10.1002/ecs2.3914
7. Shaw, B., Jordan, X. society for I. C. Foltz, & Jokela, X. society for I. C. (2022). Habitat Restoration and Management Strategies: Pollinator and Beneficial Insect Training [Video]. https://bwsr.state.mn.us/Habitat-Enhancement-Landscape-Pilot-%28HELP%29
8. Swengel, A.B. A literature review of insect responses to fire, compared to other conservation managements of open habitat. Biodiversity and Conservation 10, 1141–1169 (2001). https://doi.org/10.1023/A:1016683807033