The quills of the porcupine are not thrown or shot but easily detached after contact with a predator's flesh. Porcupines have poor vision but good senses of hearing and smell. The common porcupine is primarily found in coniferous forests but is also frequently found in deciduous or mixed forests. Highly adaptable, Erethizon dorsatum may be found in open tundra, rangeland, and deserts. When away from forests, the common porcupine usually remains in vegetated riparian areas.
Some humans consider the porcupine to be the most important mammalian forestry pest.
Individual animals gnaw woodwork, furniture, tools, saddles, and other objects that have received salt deposits from human perspiration. The common porcupine often causes death of timber and ornamental trees by girdling the bark of the trunk or stripping all of the bark abover the snowline. Their feeding habits also contribute to the injury of orchards and crop damage. The common porcupine has population cycles that range from twelve to twenty years. A period of about ten years separates the end of a decline and the beginning of a growth phase.