Piñon and juniper encroachment and infilling can alter ecosystem processes and decrease resilience and resistance in sagebrush grasslands. Land managers employ a variety of techniques to eliminate these trees and mitigate their negative effects. Mechanical mastication or shredding is an increasingly popular method of removing these trees in Utah. It is a versatile treatment that can reduce canopy fuels, increase infiltration, and reduced sediment loss. We compared vegetation cover for annual and perennial vegetation functional groups on shredded and adjacent unshredded areas across a range of sites. Our approach was to categorize sites by ecological site type (encroachment or tree) and subplots by treatment (untreated, shredded, and shredded-seeded) and initial tree cover. Mixed model analysis of covariance and the Tukey-Kramer test were used to determine significant differences among ecological site type and treatment combinations for each 5% increment of untreated or initial tree cover. Shrub cover was unaffected by treatment and decreased with increasing tree cover. In general, perennial herbaceous understory cover increased after shredding to equal or exceed initial encroachment and infilling levels. This held true for both ecological site types and treatments, even at high pretreatment tree cover percentages. Cheatgrass also increased in cover after tree shredding although this trend was dampened in the seeded treatments indicating some suppression of cheatgrass by seeding. Shredding when there is high cover of perennial herbaceous plants and shrubs or seeding in conjunction with shredding where initial tree cover exceeds 35-40% will help discourage dominance by weeds.



College and Department

Life Sciences; Plant and Wildlife Sciences



Date Submitted


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mechanical mastication, encroachment, infilling, sagebrush