Can mowing substitute for fire in semiarid grassland

Authors: Vermeire, Lance; Strong, Dustin; GATES, EMILY - Wyoming Department Of Game & Fish; MARLOW, CLAYTON - Montana State University; Waterman, Richard

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/14/2019
Publication Date: 11/6/2019
Citation: Vermeire, L.T., Strong, D.J., Gates, E.A., Marlow, C.B., Waterman, R.C. 2019. Can mowing substitute for fire in semiarid grassland. Rangeland Ecology and Management. 73(1):97-103. https://doi.org/10.1016/j.rama.2019.08.006.
DOI: https://doi.org/10.1016/j.rama.2019.08.006

Interpretive Summary: Data are accumulating that indicate the importance of fire in rangeland systems. Mowing is a common management technique sometimes considered a surrogate for fire and a safer alternative. However, direct comparisons of fire and mowing effects are limited. Our objective was to determine whether mowing can substitute for fire in rangeland by comparing effects on plant biomass, composition, cover, soil nutrients, and forage quality. Three disturbance treatments (spring fire, spring mowing and non-treated control) were randomly assigned to 21 plots (5 x 5-m) each on silty and claypan ecological sites in a completely randomized design, with seven replications per site. Current-year biomass was similar among control, mowed and burned treatments (1003, 974, 1022 ± 64 kg · ha-1). Mowing shifted functional group composition by reducing cool-season perennial grass 12% and increasing forbs 8%. Non-native species were a larger component of mowed (12%) than control (6%) or burned plots (4%). Fire increased bare ground 35%, reduced litter 32% and eliminated old dead the first growing season. Plant-available soil nitrogen and sulfur more than doubled with fire and there was a trend for more phosphorus in burned plots. Mowing effects were limited to a trend for less Fe. Mowing affected 42% of the forage quality variables with a 2% average improvement across all variables. Fire affected 84% of the variables, with a 12% average improvement. Mowing increased forage phosphorus and potassium, whereas fire increased forage concentrations of nitrogen, potassium, phosphorus, sulfur, magnesium, iron, manganese and copper. Total digestible nutrients increased 1.1% with mowing and 2.1% with fire. Digestibility increased 2.2% with mowing and 6.7% with fire. Forage from burned plots had greater fermentation rate than that from controls or mowed plots. Although mowing can be a useful management tool, it is not a substitute for the ecological effects of rangeland fire.

Technical Abstract: Data are accumulating that indicate the importance of fire in rangeland systems. Mowing is a common management technique sometimes considered a surrogate for fire and a safer alternative. However, direct comparisons of fire and mowing effects are limited. Our objective was to determine whether mowing can substitute for fire in rangeland by comparing effects on plant biomass, composition, cover, soil nutrients, and forage quality. Three disturbance treatments (non-treated control, spring mowing and spring fire) were randomly assigned to 21 plots (5 x 5-m) each on silty and claypan ecological sites in a completely randomized design, with seven replications per site. Current-year biomass was similar among control, mowed and burned treatments (1003, 974, 1022 ± 64 kg · ha-1). Mowing shifted functional group composition by reducing C3 perennial grass 12% and increasing forbs 8%. Non-native species were a larger component of mowed (12%) than control (6%) or burned plots (4%). Fire increased bare ground 35%, reduced litter 32% and eliminated old dead the first growing season. Plant-available soil N and S more than doubled with fire and there was a trend for more P in burned plots. Mowing effects were limited to a trend for less Fe. Mowing affected 42% of the forage quality variables with a 2% average improvement across all variables. Fire affected 84% of the variables, with a 12% average improvement. Mowing increased forage P and K, whereas fire increased forage concentrations of N, K, P, S, Mg, Fe, Mn and Cu. Total digestible nutrients increased 1.1% with mowing and 2.1% with fire. In vitro dry matter disappearance increased 2.2% with mowing and 6.7% with fire. Burned plots had greater in vitro fermentation than controls or mowed plots. Although mowing can be a useful management tool, it is not a substitute for the ecological effects of rangeland fire.