Timing of prescribed fire
Impacts on rangeland composition and cattle performance
By Jason M. Warner
Prescribed burning has long been practiced during spring in the Kansas Flint Hills as a means to not only improve forage production from native warm-season grasses but also allow for increased stocker cattle performance. Likewise, control of invasive species on native tall-grass pastures is key benefit of strategic fire. While burning in the spring has traditionally been done, unpredictable wind and low-humidity that time of year can make fires difficult to manage and time periods of concentrated burning can also present issues with air quality.
Regarding mitigation of invasive species, sericea lespedeza is an aggressive perennial legume and infestations throughout the Flint Hills have been widespread in recent years. Late-summer or fall prescribed fire has been shown to hinder the proliferation of sericea lespedeza, yet the impact on stocker cattle performance and plant composition in subsequent years has not been well documented.
To better understand these dynamic relationships, a multi-year study was recently completed by researchers in the Department of Animal Sciences and Industry at Kansas State University (Duncan et al., 2024). This six-year trial was done at the Kansas State University Beef Stocker Unit near Manhattan, Kansas from June 2018 to August 2023 utilizing 18 pastures assigned to one of three prescribed-fire treatments (n = 6 pastures per treatment): April, August or October burning. All burn treatments were applied prior to grazing, and soil cover, plant species composition, and standing forage biomass was also determined. Yearling cattle (n = 1,939; initial body weight approximately 620 lb; heifers yr 1; steers yr 2-5) across five consecutive years, beginning in 2019, grazed treatment pastures for 90 days at a targeted density of 250 lb of live-weight per acre.
After five consecutive grazing seasons, both average daily gains and total weight gains (Table 1.) were improved for calves grazing spring-burned pastures compared with those that grazed either summer- or fall-burned pastures. While the response in cattle performance between spring and the later-season burning treatments was likely attributed to differences in grazed diet quality, interestingly cattle performed similarly when grazing either August or October burned pastures.
Regarding rangeland productivity, standing forage biomass was similar among prescribed-fire treatments while the proportion of bare soil was greater for spring than either summer or fall-burned pastures (Table 2.). Concurrently, litter cover as a % of total area was significantly greater for pastures burned in the summer relative to other times, which was due to soil cover being measured annually in June. Thus, as the length of time between fire application and sampling increased, proportions of bare soil decreased while proportions of litter on the soil surface increased. However, total basal vegetation cover (as a % of the total area) was not impacted by time of prescribed fire.
Pertaining to basal vegetation cover, both cover (as a % of total vegetation cover) of total grasses and native grasses were not influenced by timing of prescribed-fire. The time at which burning was applied tended to impact the proportion of C3 and C4 grasses in experiment pastures. There was a tendency for increased cover of C3 grasses in both summer and fall-burned pastures.
An opposite impact was observed for C4 grasses, with the greatest in spring-burned and the least in fall-burned pastures suggesting that when fire is applied can ultimately influence grass growth patterns and species present. The proportion of basal cover comprised of total forbs and native forbs did not appear to be impacted by timing of prescribed fire. When analyzing forage composition data regarding the presence of shrubs, total shrubs tended to be more frequent in pastures burned later in the year compared with pastures burned earlier in the spring.
Overall, data from this large multi-year study suggest that the timing of prescribed burning may impact stocker cattle performance during a 90-day grazing season typical of the Kansas Flint Hills in addition to relatively minor changes in rangeland plant composition. Therefore, if producers look to implement late-season prescribed fire as a method to manage sericea lespedeza infestations, costs of burning relative to chemical control must be weighed in relation to potential changes in revenue due to cattle performance. This gives producers flexibility with planning and implementing prescribed fire to not only conduct burns at times of the year when conditions are ideal, but also apply strategic burning to targeted rangelands to which long-term shifts in species presence are desired while still meeting cattle performance goals.
References:[1] Duncan, Zachary M.; Tajchman, Alan J.; Lemmon, Jack; Hollenbeck, William R.; Blasi, Dale A.; and Olson, K. C. (2024) "Long-Term Effects of April, August, or October Prescribed Fire on Yearling Stocker Cattle Performance and Native Rangeland Plant Composition in the Kansas Flint Hills," Kansas Agricultural Experiment Station Research Reports: Vol. 10: Iss. 1.
Warner is an Extension cow-calf specialist in the Department of Animal Sciences and Industry at Kansas State University.
