Mechanical mastication (shredding) is an increasingly popular method of removing piñon and juniper trees in Utah. We compared vegetation cover on shredded or shredded/seeded and adjacent unshredded areas on 44 sites. The objective of this study was to evaluate how ecological site (sagebrush-encroached or tree sites), treatment, and pretreatment tree cover affected the response of the functional groups (shrubs, perennial herbaceous understory, and cheatgrass) of interest. Mixed model analysis of covariance and the Tukey test were used to determine significant differences among ecological site type and treatment combinations for each 5% increment of pretreatment tree cover. Shrub cover was unaffected by treatment.  Generally, shredding increased perennial herbaceous understory cover on both ecological site types, even at high pretreatment tree cover. This was especially true for the shredded/seeded treatment. Cheatgrass also increased in cover with tree shredding although to a lesser extent on shredded/seeded treatments, indicating some suppression of cheatgrass by seeding. Tree shredding not only reduces canopy fuels and facilitates fire suppression, but also maintains shrub cover and stimulates growth of desirable perennial herbaceous species. Appropriate management of PJ forests based on ecological site and tree cover can better create and maintain a productive understory.
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