Get reliable rangeland science

The role of livestock grazing on fuel loads and fire behavior is important to land managers, land owners, and the general public across rangelands. Livestock grazing affects the amount and spatial distribution of herbaceous biomass, e.g. fine fuels, affecting the potential for fire spread, intensity, and fuel consumption. Grazing can be targeted at spatial scales varying from the feeding station to the pasture scale. In addition, environmental variables such as fuel moisture, topography, and wind influences fire behavior. To better understand these complex interactions we conducted a modeling experiment using the physics based model Wildland Urban Interface Fire Dynamics Simulator (WFDS). The model is applicable to heterogeneous fuel beds and has been validated with field experiments in grasslands. In this model experiment we reduced herbaceous fuels by 10%, 25%, and 50%, wind speed was held at 7.2, 18.0, and 36.0 km/h, and fuel moisture was simulated at 6%, 10%, and 17%. Fuel reduction was applied at spatial scales varying from 1.5 to 20 m. Under these conditions the fire rate of spread varied between 1.8 and 7.2 km/h, increasing with higher winds and lower fuel moistures as expected. The fire did not spread in simulations with 17% fuel moisture or in simulations with 50% biomass removal, except at low fuel moisture and high wind. The fire was less likely to spread when the biomass removal was patchy compared to homogeneously applied across the grassland and the spatial scale of the grazing treatment influenced fire spread.