Porcupine damage to trees: stripped bark in the crown, as extension services describe it

This page reports what the official source says. It is not legal advice: ask the office named here. The Utah State University note below quotes Utah Division of Wildlife Resources code R657-3 on animals classed as controlled, and the University of Maryland note says the porcupine is a watchlisted species in Maryland. Rules on porcupines differ by place and the state wildlife agency is the office that applies. The page describes what the sources say the damage looks like and the guards they list. It does not say what to do about any tree or animal. For protected species and nests in tree work, see the guide on wildlife and the law.

What the damage looks like

Utah State University Extension Forestry (Utah Forest Facts 038) says porcupines favor young bark, leaves and end twigs, which are mostly up in the crown of a mature tree, though they will strip bark from any part of a trunk or branch. Like beavers, it says, they want the nutritious inner bark, the phloem, so they remove the bark right down to the cambium, where the wood begins. It names grooved tooth marks of about 5 mm as characteristic, and says squirrels and other small mammals also remove bark but leave smaller tooth marks. See the page on tree squirrel damage.

The University of Maryland Extension (Woodland Wildlife Spotlight, updated September 30, 2022) says porcupines eat evergreen needles and the inner bark of trees in winter and may even girdle a tree, causing long-lasting damage or death, then shift in spring and summer to berries, seeds, grasses, leaves, roots and stems. University of New Hampshire Extension (The Porcupine and the Wolf Tree, May 18, 2020) says they climb with large claws to eat bark, buds and foliage from a variety of trees, with a winter diet of bark, needles and buds from mostly hemlock in the northeast, and that they den in hollow trees, rock crevices, hollow logs or other animals' dens, with a large scat pile at the entrance as the most obvious sign.

Which trees and when

Utah State says that in the interior West, cottonwoods, willows, pines, Douglas-firs, spruces and true firs are preferred, especially for their bark, though they eat nearly any vegetation and also damage fruit trees. It says deep snow is hard for them to move through, which adds winter pressure to find food they can reach, and that through the winter they feed mainly in the canopy, chewing needles, bark, twigs and buds off trees. Maryland names the eastern hemlock as one of their favorite trees and notes that the hemlock woolly adelgid is putting that tree under pressure.

Whether the sources call it harmful

Utah State says that if bark is stripped in to the cambium that part of the tree will die, though small wounds may heal from the edges, and that if the bark is removed all the way around a trunk or branch the part above that point is killed. It says this weakens the tree and makes it more open to disease, insects and birds. It also says porcupine presence in forests improves their diversity: damage can suppress some tree growth, opening the canopy and stimulating understory plants, and trees killed or felled provide shelter and nest sites for other wildlife. It reports substantial economic loss to commercial timber, nurseries and orchards.

Guards and rules the sources list

Utah State says fencing is the most effective way to prevent porcupine damage to trees, and lists woven wire fencing around gardens and orchards, with an electric wire added to the top. For individual large trees it lists a band of aluminum flashing around the trunk to block access at ground level, or wire mesh or hardware cloth around the trunk, and warns that such materials must be monitored because they can damage or girdle the tree if left on too long. It says no registered repellent or toxicant has been proven effective for porcupines, and that removal or relocation is nearly impossible because porcupines keep moving through forests in search of food and shelter.

On the rules, Utah State says the Utah Division of Wildlife Resources code requires a certificate of registration before collecting, importing, transporting or possessing animals classed as prohibited or controlled, that the state considers the porcupine controlled for collection, importation and possession, and that it suggests contacting a professional wildlife control officer for a nuisance porcupine. Maryland says the porcupine is not federally endangered but is watchlisted in the state, meaning it needs conservation, and gives slow reproduction, vehicle strikes and loss of hemlock as pressures on it.

The other animals in this group are listed on the wildlife damage to trees page.