Nader et al. survey herbicides, prescribed fire, mechanized treatments, hand cutting, and grazing animals as fire management techniques. Managing vegetation involves “changing the plant community to decrease the flame height when fire occurs,” favoring native species that may be more resilient to fire, and altering the landscape to create fuel breaks, which are patches across which it is hard for fire to jump [Nader 2007: 18].
Focusing their analysis on grazing and the contexts in which it is most useful, the authors note that there are many site and animal specific factors to take into account for successful implementation.
[Grazing] is a complex, dynamic tool with many plant and animal variables, and it requires sufficient knowledge of the critical control points to reach treatment objectives. Those control points involve the species of livestock grazed (cattle, sheep, goats, or a combination); the animals’ previous grazing experience (which can affect their preferences for certain plants); time of year as it relates to plant physiology (animal consumption is directed by the seasonal nutrient content); animal concentration or stocking density during grazing; grazing duration; plant secondary compounds; and animal physiological state [Nader 2007: 19].
Grazing has the advantage of keeping nutrients in the ecosystem, unlike mechanical methods that harvest vegetation to be sold as biomass chips (like wood chips). This means that when animals digest vegetation and excrete on the landscape, they participate in the local nutrient cycle. Animals also trample soil, which can crush fine fuel and mix it into the soil, where it cannot contribute to ignition, which reduces one contributing factor to persistent and destructive blazes. Animals do more than just remove extra vegetation – they can have many beneficial interactions within a given ecosystem.
Any grazing plan designed for fuel reduction needs to consider the grazing impacts on parameters other than just simply reduction. The effects of the grazing management should be studied for their impact on water quality, compaction, riparian vegetation, disease interaction with wildlife (bluetongue, pasturella), and weed transmission. The positive aspects of grazing over other treatments also should be weighed, including recycling of nutrients into the products of food and fiber [Nader 2007: 22].
By introducing grazing animals into a landscape or agricultural system, managers can affect biodiversity in complex ways. The authors mention that “Hadar et al. reported that light grazing increased plant diversity on treated sites. Thus, when proposing a stocking rate for treatment consumption, the environmental impact needs to be considered” [Nader 2007: 22].
Nader et al. conclude that “grazing is best used when addressing vegetation with stems of smaller diameters that make up the 1- and 10-hour fuels. These two fuel classes are important because they can greatly impact the rate of spread of a fire, as well as flame height” [Nader 2007: 19]. While they call for further research to validate anecdotal accounts supporting grazing and understand its best practice, they maintain that “prescribed grazing has the potential to be an ecologically and economically sustainable management tool for reduction of fuel loads” [Nader 2007: 20].
Nader, Glenn et al., 2007, Planned Herbivory in the Management of Wildfire Fuels: Grazing is most effective at treating smaller diameter live fuels that can greatly impact the rate of spread of a fire along with the flame height, Rangelands 29(5), https://doi.org/10.2111/1551-501X(2007)29[18:PHITMO]2.0.CO;2.