The North American porcupine (Erethizon dorsatum) is a large rodent and specialized herbivore found across diverse habitats. Porcupines definitively eat trees, as tree material is a significant part of their diet. They primarily target the living inner bark and the cambium layer, which is the thin, growth-producing layer beneath the outer bark. This feeding habit is a natural part of their ecology, but it can cause substantial damage to individual trees.
The Porcupine’s Winter Diet: Why They Target Trees
Porcupines are active throughout the year and do not hibernate, necessitating a continuous food supply even when temperatures drop. During warmer months, their diet consists of ground vegetation, including leaves, forbs, and buds from deciduous trees. This protein-rich food source disappears as winter sets in.
Winter forces the porcupine to transition to a diet of evergreen needles, twigs, and bark. They seek the inner layer of the bark, known as the phloem, because it is the most nutrient-dense part of the tree. Although this winter diet is low in nutritional quality, it is the most dependable source of calories and fiber available in the cold season.
This behavior is driven by the need to maintain energy, making winter a nutritional bottleneck for the species. Porcupines possess a specialized digestive system that allows them to process this high-fiber, low-quality food source efficiently. They prefer species like hemlock, white spruce, ponderosa pine, sugar maple, and apple trees, often feeding high in the canopy where the most tender parts are found.
Identifying Signs of Porcupine Feeding Damage
Identifying porcupine damage relies on recognizing the characteristic signs left by their large incisor teeth. The most apparent evidence is the removal of bark in irregular, deep patches, often revealing the lighter-colored wood underneath. These gnaw marks are typically grooved and about 5 millimeters wide, differentiating them from the smaller marks left by squirrels or other rodents.
Porcupines target the main trunk, upper limbs, or feed high in the canopy. The most serious damage is girdling, which occurs when the animal removes the bark completely around the circumference of a branch or the main trunk. Removing the phloem and cambium layers severs the transport of water and nutrients, essentially starving the tree or branch above the damaged section.
Girdling is often fatal to the tree or limb because the severed vascular system leads to eventual death from the point of damage outward. Secondary signs of porcupine presence include clipped twigs that have fallen below the feeding site. Property owners may also find large, oval-shaped droppings or shed quills at the base of a damaged tree.
Methods for Protecting Trees
Protecting individual, high-value trees from porcupine damage often involves physical exclusion methods. One effective technique is to install a metal band or aluminum flashing at least 30 inches wide around the trunk. This barrier must be secured tightly to prevent the porcupine from climbing the trunk to reach the canopy.
For smaller trees or orchards, a wire mesh fence or hardware cloth can enclose the area entirely. Since porcupines are skilled climbers, fencing should be a minimum of 18 to 24 inches high with the top edge bent outward at a 65-degree angle. Burying the bottom of the wire a few inches below ground level prevents them from digging underneath.
Chemical repellents applied to trees have shown limited and inconsistent effectiveness against porcupines. Habitat modification, such as removing potential den sites like rock piles or brush, can discourage them from staying in a particular area. Providing an alternate source of salt, which porcupines seek, may also redirect their attention away from wooden structures and trees.