Targeted Cattle Grazing to Alter Fuels and Reduce Fire Behavior Metrics in Shrub-Grasslands

Abstract

Wildfire is an increasing concern throughout the world, with wildfires increasing in size, frequency, suppression cost, and loss of lives and resources. Targeted grazing has been suggested as a tool to establish and maintain strategic fuel breaks by reducing the fine herbaceous fuel load and subsequently fire behavior metrics. In a full factorial replicated experimental design, we evaluated the effect of domestic cattle grazing at two seasons (summer and fall) and two utilization levels (low and moderate) on fuel characteristics and fire behavior metrics in two big sagebrush (Artemisia tridentata Nutt.) communities. Shrub cover and herbaceous biomass before and after grazing were estimated in 2014 and 2015. Grazed and control plots were burned in late September 2015 under low fuel moisture conditions; flame height and fire rate of spread were measured. Cattle grazing reduced the herbaceous fuel load and grass height and increased herbaceous litter cover on the soil surface following the short-term grazing treatments. The more intensely plots were grazed also resulted in lower fuel loads than less intensely grazed plots. The season of grazing did not affect herbaceous fuel loads at the time of prescribed fire because utilization of grasses and forbs varied by season resulting in similar herbaceous biomass among both seasons of grazing at the time of the prescribed fire. Grazing was found to be an effective tool at altering herbaceous wildland fuels, which reduced fire behavior metrics when shrub cover was below 18%. Flame height was positively correlated with the amount of herbaceous vegetation, grass height, and annual grasses in the plant community at low shrub cover. However, at higher shrub canopy cover (>18%), cattle grazing for fuel reduction and alteration was limited due to low herbaceous biomass and the wildfire's potential to carry through the shrub canopy.