Can Mowing Substitute for Fire in Semiarid Grassland?☆
Introduction
Land managers are becoming more aware of the benefits of prescribed fire. However, people are commonly hesitant to begin a burning program because they lack experience applying prescribed fire. Among the mechanisms believed to cause fire effects are nonselective biomass removal and increased light availability near the soil surface. Therefore, it is occasionally suggested that some fire effects can be mimicked with high-intensity, short-term grazing or mowing.
Land managers in rangeland ecosystems recognize the restoration of certain ecological processes (e.g., fire, livestock grazing) as an efficient strategy for improving and maintaining rangeland plant community structure and function (Wright and Bailey, 1982, Milchunas et al., 1988). The effect of fire and grazing on rangelands varies by ecosystem, as some rangeland plant communities are more resilient to fire or grazing (Wright and Bailey, 1982). Prescribed fire and grazing have been used in tandem in tallgrass prairie to enhance forage quality, improve livestock weight gain, reduce woody encroachment, improve wildlife habitat, and increase plant diversity (Hobbs et al., 1991, Collins et al., 1998, Fuhlendorf and Engle, 2004, Joern, 2005, Scasta et al., 2016). Relative to tallgrass prairie, sagebrush steppe rangeland is more susceptible to damage from fire and grazing (Mack and Thompson, 1982, Wright and Bailey, 1982, Chambers et al., 2014). However, prescribed fire and grazing may still be used in the sagebrush steppe ecosystem to maintain productive native plant communities (Davies et al., 2010, Davies et al., 2016). Whether used individually or in combination, fire and grazing are valuable land management tools that can be used to fulfill various ecosystem management objectives (Pöyry et al., 2004, Fuhlendorf et al., 2009, Pyke et al., 2010).
Fire and grazing share certain ecological characteristics; both processes remove plant biomass, convert plant material to biotic and abiotic materials, and have the potential to alter ecosystem properties, including nutrient dynamics, plant production, and diversity (Howe, 1995, Collins et al., 1998, Hart and Ashby, 1998, Wan et al., 2001, Koerner and Collins, 2014). Fire has the potential to produce direct plant mortality in certain species, particularly annuals, and improve overall forage quality of a plant community (Vermeire and Rinella, 2009, Strong et al., 2013, Dufek et al., 2014). Furthermore, fire differs from grazing in that fire does not choose what plants to “consume,” does not have nutrient requirements, removes plant biomass at a relatively uniform utilization level (Bond and Keeley, 2005), and can have direct effects on the animal community (Branson and Vermeire, 2016). In contrast, grazing may cause direct fluctuations in plant community composition and indirectly alter forage quality (Taylor et al., 1993, Vermeire et al., 2008). Hulburt (1988) suggested clipping and fire largely had similar effects in tallgrass prairie in that both increase soil temperature and increase light intensity at the soil surface. However, biomass and reproductive culm density were positively related to nitrogen addition, which is associated with fire. Therefore, while fire and grazing share similar physiognomy, both have the proclivity to set plant communities on distinct ecological trajectories.
Mechanical removal (mowing) of vegetation shares characteristics with fire and grazing (uniform utilization and incomplete vegetation removal) and has been used to test for differences between defoliation mechanisms (Cox, 1988, Moog et al., 2002, Fidelis et al., 2012). Mowing requires less planning than livestock grazing and prescribed fire and may reduce risk compared with fire. Another benefit is the relative ease of mowing applications, which makes it an attractive vegetation management alternative to livestock grazing or prescribed fire. However, as outlined previously, fire and grazing are unique ecological processes and mowing may not reasonably mimic or have the magnitude of effects that the restoration of fire or grazing could have on a rangeland ecosystem (Lodge, 1960, Prober et al., 2008, Kitchen et al., 2009, Pyke et al., 2014).
The objectives of this study were to 1) describe spring mowing and spring prescribed fire effects on plant biomass, composition, cover, soil nutrients, and forage quality; and 2) to contrast the two treatments to each other and nontreated control plots and determine whether mowing is a suitable substitute for fire in rangeland. We hypothesized that spring fire 1) reduces annual grasses and forbs, 2) reduces litter and increases bare ground, 3) increases soil nutrient availability, and 4) increases forage quality to a greater extent than spring mowing.
Section snippets
Study Area
Research was conducted on the Fort Keogh Livestock and Range Research Laboratory (46o23′32′′N, 105o57′09′′W; 809 m above sea level), near Miles City, Montana. The vegetation type is northern mixed prairie. The climate is semiarid, with 341 mm average annual precipitation, 110- to 135-d freeze-free period, and temperatures ranging from − 40oC to 38oC. About 90% of annual net primary production occurs by 1 July (Vermeire et al., 2009) and is most affected by April and May precipitation (Vermeire
Biomass and Cover
Current-yr biomass was similar among control, mowed, and burned treatments (1 003, 974, 1 022 ± 64 kg ● ha− 1, respectively; P = 0.7538). Despite the similarity in production, mowing shifted functional group composition relative to control and burned plots by reducing C3 perennial grass (P = 0.0029) and increasing forbs (P < 0.0001; Fig. 1). No differences were detected among treatments for C4 perennial grass (P = 0.7802) or annual grass (P = 0.3725). Across functional groups, non-native species
Discussion
Early spring mowing caused changes in functional group composition and diversity and improved some measures of forage quality, whereas spring fire did not alter functional group composition or diversity. However, fire increased bare ground through litter reduction, increased plant-available soil nutrients, and improved forage quality of current-yr growth. The hypothesis that spring fire reduces annual grasses and forbs was not supported by the data, but results supported the hypotheses that
Implications
Many rangelands evolved with recurrent fire, grazing, and variable weather. Two of the three, fire and defoliation, can be manipulated through management and both, operating in tandem, are likely required to maintain rangeland integrity. Defoliation can mimic fire in reducing standing biomass and has been successfully employed for species-specific management. However, fire effects are more complex than simply reducing standing biomass. Mowing-induced changes in functional group composition and
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Cited by (12)
Clipping Height and Frequency Effects on Japanese Brome Seed Production and Viability
2023, Rangeland Ecology and ManagementFire and Nitrogen Effects on Aristida purpurea Mineral Concentrations
2023, Rangeland Ecology and ManagementGrazing and defoliation timing effects in Great Plains ponderosa pine woodland following a large summer wildfire
2022, Forest Ecology and ManagementCitation Excerpt :Early grazing may be preferable considering there were no negative effects on productivity, reduction of non-native composition and increased diversity. Early grazing is further supported by the tendency for fire induced increases in forage quality to be greatest during the early growing season (Augustine and Milchunas, 2009; Waterman and Vermeire, 2011; Dufek et al., 2014; Vermeire et al., 2020). Our observations in Great Plains ponderosa pine woodland were similar to previous research indicating post-fire defoliation has no negative effect on herbaceous production in northern mixed-grass prairie (Vermeire et al., 2014; Gates et al., 2017a; 2017b; Vermeire et al., 2018; Powell et al., 2018).
Annual bromes decrease with increasing fall defoliation intensity
2021, Global Ecology and ConservationCitation Excerpt :Despite the potential advantage of additional seed removal with spring defoliation, the period for maximizing this effect and minimizing effects on perennials is brief (Haferkamp and Karl, 1999; Harmoney, 2007). Although mowing to 7.3 cm during spring did not affect non-brome grass biomass (Reinhart et al., 2020), mowing to 6 cm during May reduced C3 perennial grass composition and increased forbs (Vermeire et al., 2020). Fall grazing reduced cheatgrass seedbank to about half of that in non-grazed sites (Perryman et al., 2020).
Individual and combined effects of fall fire and growth-regulator herbicide on annual bromes
2021, Rangeland Ecology and ManagementCitation Excerpt :Japanese brome seeds are readily killed by fire, even with light fuel loads (Vermeire and Rinella 2009) and cheatgrass seeds likely are as well. This would direct interest to fire effects on postfire seed production when increased nutrient availability (Reinhart et al. 2016; Vermeire et al. 2020) or lower brome density and reduced intraspecific competition could result in greater seed quantity or quality (Young and Evans 1978; Whisenant 1990; Rice and Mack 1991; Beckstead et al. 2011). Interestingly, individual annual brome plants were visibly larger in burned than nonburned plots during 2018.
Effects of mowing regimes on above- and belowground biota in semi-arid grassland of northern China
2021, Journal of Environmental ManagementCitation Excerpt :However, grazing is a selective disturbance that reduces the abundance of grazing-sensitive plant species (e.g., palatable or tall) (Wang et al., 2020). Fire is often described as having positive effects on subordinate and early-successional plant species, and could increase the plant N availability, mainly via ash deposition and root death and by enhancing the N mineralization rate (Vermeire et al., 2020). Fire, however, has negative effects on vegetation because fire tends to suppress annual grass biomass, which commonly causes declines in plant species richness and total annual productivity (Yang et al., 2020).
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This work was partially supported by the US Forest Service (13-IA-11011800-012). Mention of any trade name or proprietary product does not constitute a guarantee or warranty by the authors or US Dept of Agriculture − Agriculture Research Service (USDA-ARS), nor does it imply the approval of these products to the exclusion of others. The USDA-ARS, Plains Area, is an equal opportunity/affirmative action employer, and all agency services are available without discrimination.