Porcupines eat herbaceous plants, inner tree bark, twigs, and leaves, with an apparent preference for ponderosa pine, aspen, willow, and cottonwood. Trees with thin, smooth bark are preferred over those with thick, rough bark. Porcupine feeding is frequently evident and has considerable impact on the cottonwood stands of western river bottoms. They will also gnaw on the wooden handles of tools to get the salt left by perspiration.
Resources: (online)
Porcupine Control
