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Porcupines (Erethizon dorsatum) rely on trees and shrubs for winter food and can cause serious, localized damage to conifers. Twenty-two percent of ponderosa trees (Pinus ponderosa) examined in southeastern Washington were damaged by porcupines. Most damage involved complete girdling of the mid- to upper boles of the larger trees (12 to 30 cm dbh) in the stand. Preliminary repellent trials with captive porcupines suggested that several materials might reduce tree damage, especially predator-associated odors. Field trials are needed to assess efficacy and duration of protection under ambient winter conditions.