Pinyon-juniper woodland encroachment threatens ecosystem function and diversity on sagebrush steppe. Decreased fire frequency likely favors proliferation of pinyon-juniper woodlands and subsequent decline in desirable understory species. Increased tree cover produces hazardous canopy fuel loads that contribute to severe crown fires and threaten life and property at the wildland-urban-interface. Mechanical mastication converts large canopy fuels into small woody debris, altering wildfire dynamics from a potential crown fire to a more controllable surface fire. We measured fuel loading and cover on untreated, masticated, and masticated + burned treatments on 30-m transects within 30 X 33-m subplots, representing 45 different sites throughout Utah. All variables were analyzed using mixed-model analysis of covariance with untreated or pretreatment tree cover as the covariate. Shredding trees reduced large-diameter fuels to primarily 10-hour fuels (6.4-25.4 mm diameter). Reduced fuel sizes, fuel redistribution, and fuelbed compactness resulting from mastication treatments can aid wildfire suppression. Masticated + burned treatments effectively reduced woody surface fuel loading to that of pretreatment conditions. Prescribed burning could be used outside the growing season in cool-weather, high-moisture conditions to remove surface fuels, mitigating lethal soil heating and plant mortality. Shrub loading was not adversely affected by mastication treatments, but was significantly reduced with masticated + burned treatments. Masticated and masticated + burned treatments significantly increased herbaceous fuel loading. Treating at lower tree cover values reduced fuel buildup, and provided more opportunity for a positive herbaceous response. Fuel loading estimates measured in this study were provided to populate fire behavior models for mastication treatments on our study sites when such models become available.



College and Department

Life Sciences; Plant and Wildlife Sciences



Date Submitted


Document Type





Mechanical mastication, pinyon-juniper woodlands, fuel loading, fire, decomposition