Targeted Grazing in Southern Arizona: Using Cattle to Reduce Fine Fuel Loads

Abstract

Managing the risk of wildfires is a growing concern in the western United States. Targeted grazing, or managing livestock grazing to achieve specific vegetation goals, is one possible tool to treat fuels, but few studies have evaluated its efficacy. The goal of this study was to test the effect of targeted grazing on herbaceous fuel loads and fire behavior by 1) implementing targeted grazing in a field experiment and 2) using a fire model (BehavePlus) to evaluate changes in fire behavior resulting from treatments. We applied targeted cattle grazing using low-stress herding and strategic placement of low-moisture block supplement on rugged rangelands in southwestern Arizona using a herd of 58 Red Angus cows and two bulls. Six of the cows were initially fitted with global positioning system collars. We tested two grazing treatments: 1) herding and supplement versus 2) no herding and no supplement on two pairs of study sites and replicated this for 2 years. Herding and supplement affected both the distribution of cattle and herbaceous fuel loads. Despite light utilization (26%) in treated sites, the BehavePlus fire model predicted that herding and supplement reduced fire rate of spread by more than 60% in grass communities and by more than 50% in grass/shrub communities. Fuel treatments dropped flame lengths below a 1.2-m critical threshold under the moderate fuel moisture scenario in grass communities and below a 2.4-m critical threshold in grass/shrub communities under both moderate and extreme fuel moisture scenarios. These results suggest that targeted grazing could reduce the potential cost of fighting fires in conditions similar to this study site. However, implementing this type of treatment on other sites will require careful calibration of animal numbers, supplement amounts, and length of herding periods relative to the specific context and goals.