Dozens of animal species strip bark from trees, ranging from black bears and red deer to grey squirrels, elephants, primates, woodpeckers, and various insects. The behavior is far more widespread than most people assume, and the reasons behind it are just as varied: some animals are after the sugary, nutrient-rich tissue beneath the outer bark, while others strip bark as a byproduct of territorial marking, tooth maintenance, or nest building. Which animal is responsible in a given case depends heavily on geography, the tree species involved, and the telltale pattern of damage left behind.
Bears
Bears are among the most dramatic bark strippers in temperate forests. In the Russian Far East, Asiatic black bears peel bark from fir trees to reach the cambium, the thin layer of actively growing tissue just beneath the bark surface. They bite into the trunk, sometimes standing on their hind legs, and pull strips of bark downward (or occasionally upward), then lick the flowing sap and scrape off the cambium layer with their teeth, leaving long vertical grooves on the exposed trunk. Research on Manchurian fir in Russia’s Primorsky region found that this feeding peaks between June and mid-July, when the cambium is most active and easiest to peel away.1PubMed Central. Biochemical Content of Cambium of Abies nephrolepis Eaten by Bears on the Far East of Russia On Sakhalin Island, the same behavior extends through July and into early August on hardwood trees.
In North America, black bears strip the bark of Douglas fir, western red cedar, and other commercially valuable conifers in the Pacific Northwest. The damage tends to concentrate on fast-growing trees in the spring, when the sapwood beneath the bark is highest in sugar content. A single bear can damage dozens of trees in a season, leaving behind claw marks and tooth scrapes that are usually unmistakable. The grooves carved into exposed wood are typically around 10 to 30 centimeters long and a few millimeters deep, and the stripped patches often spiral partway around the trunk.
Deer and Elk
Red deer and elk are responsible for widespread bark damage across European and North American forests. Unlike bears, deer do not have upper front teeth, so they grip the bark with their lower incisors and pull upward, creating ragged vertical strips. This behavior is most common in winter and early spring, when other food sources are scarce and the inner bark provides calories. Antler rubbing in autumn is a separate issue and tends to shred bark in shorter, more localized patches on young trees.
A large-scale study of Norway spruce stands found that about three-quarters of all surveyed tree stands showed some bark-stripping damage from red deer. On average, roughly 16% of trees in a given stand were affected, though in about one in nine stands more than half of the trees had been stripped. The strongest predictor of damage was simply how many deer lived in the area; the probability of stripping rose sharply once deer density passed a certain threshold. Stands near farmland and in productive growing sites were hit harder, while stands closer to roads saw less damage, likely because deer avoid human activity.2Wildlife Biology. Risk factors for bark stripping damage on Norway spruce by red deer
Elephants
African elephants are perhaps the most consequential bark strippers on the planet. In savannas and woodlands, elephants strip bark using their tusks and trunks, sometimes peeling off massive sheets that expose the trunk all the way around. A five-year study in Tanzania’s Serengeti found that chronic, repeated bark stripping by elephants was the dominant driver of overstorey tree mortality, outweighing fire and drought as causes of death. Trees that were stripped repeatedly over time fared worse than those that suffered a single severe episode, meaning the cumulative toll of low-intensity damage mattered more than any single dramatic event.3Journal of Ecology. Elephant damage, not fire or rainfall, explains mortality of overstorey trees in Serengeti
Elephants are also selective about which species they target. In the Serengeti study, certain acacia species were stripped far more often than their abundance would predict, while other species were largely left alone. One particularly vulnerable species experienced a mortality rate above 70% over the five-year study period when elephants targeted it. This selectivity means elephant bark stripping can reshape the composition of an entire woodland over decades, favoring species that elephants ignore and driving out those they prefer.
Squirrels and Other Rodents
Grey squirrels are a well-documented cause of bark stripping in the United Kingdom and parts of continental Europe, where they damage young broadleaf trees, particularly beech and sycamore. Research in British woodlands found that the amount of bark each squirrel stripped from a tree was strongly related to the thickness of the phloem, the tissue that transports sugars through the tree. Trees with wider phloem lost more bark, while sugar concentration in the phloem did not predict damage. Fast-growing plantations tend to have thicker phloem, which helps explain why managed woodlands suffer disproportionately. The same study noted that bark stripping correlated with the density of juvenile squirrels, suggesting that young animals may initiate the behavior through exploratory gnawing or social conflict, with older squirrels continuing the habit once learned.4Journal of Zoology. Bark‐stripping by Grey squirrels (Sciurus carolinensis)
Porcupines are another significant bark stripper, especially in North America. North American porcupines feed heavily on the inner bark of pines, hemlocks, and other conifers during winter months when foliage and ground vegetation are unavailable. Their incisor marks leave distinctive parallel grooves, and their feeding often concentrates high in the canopy, where they may girdle individual branches or even the main stem. In southern Europe, crested porcupines have also been documented stripping bark from various tree species.
Rodent gnawing in general may be partly self-reinforcing. Research into the neural circuitry of rodent gnawing has identified a brainstem pathway that links the physical sensation of biting with reward signals in the brain, meaning that the act of gnawing itself can be pleasurable and motivating for rodents, independent of the nutritional value of what they are chewing.5PubMed Central. The rewarding crunch: A brainstem circuit links incisor mechanosensation to motivated gnawing This helps explain why squirrels and porcupines sometimes strip bark from trees they do not appear to eat.
Beavers
Beavers are the most conspicuous tree-harvesters among rodents, though their relationship with bark is more complex than simple stripping. Beavers fell entire trees to build dams and lodges, and they eat the inner bark of branches as a major food source. They also stockpile branches underwater in autumn to create food caches for winter. Interestingly, beavers appear to process some species of wood by leaving branches submerged for days before eating them. Research at a biological field station in New York found that beavers consumed quaking aspen almost immediately but left witch hazel branches in the water for two to four days before eating them, unlike any other tree species tested.6PubMed. Food processing by animals: do beavers leach tree bark to improve palatability? The soaking period may leach out unpalatable compounds, making the bark more pleasant to eat.
Beaver damage is easy to distinguish from other animals: the classic hourglass-shaped gnawing pattern on a trunk near ground level, with large wood chips scattered around the base, is unmistakable. Beavers also leave smooth, chisel-like tooth marks rather than the ragged tears typical of deer or the claw marks of bears.
Primates in Commercial Forests
A less widely known group of bark strippers is non-human primates. A review of the global literature found that at least thirteen primate species have been recorded stripping bark from commercially valuable trees. Three species account for the bulk of reported plantation damage: chacma baboons in southern Africa, black capuchin monkeys in South America, and Sykes’ monkeys in East Africa. Most of the damage occurs in pine plantations across five African and two South American countries.7US EPA HERO. Primates bark-stripping trees in forest plantations – A review
The most widely cited explanation is that primates turn to bark when their natural food supply runs short, treating the soft inner bark as an emergency calorie source. The review noted that eucalyptus bark may attract primates specifically because of its high sodium content, a nutrient that is often scarce in tropical and subtropical diets. Pine bark, by contrast, appears to be targeted for its sugary phloem, and primates tend to strip pines during the growing season when the bark peels away more easily. This seasonal pattern mirrors what has been observed in squirrels and bears, suggesting that the accessibility of the inner bark matters as much as its nutritional content.
Birds That Drill and Strip Bark
Several bird species damage bark, though their impact is usually more localized than that of mammals. Sapsuckers, a group of North American woodpeckers, drill neat rows of small holes through the bark to feed on the sap that wells up. The holes are typically arranged in horizontal or slightly spiraling lines around the trunk, and sapsuckers return repeatedly to the same tree to reopen wells and feed on both the sap and the insects it attracts. Ponderosa pine and birch are among the most frequently targeted species.
Three-toed woodpeckers in Scandinavia and boreal forests also exploit phloem sap, though their approach is somewhat different. These birds flake off scales of bark to access sap, mostly in springtime. Research in Sweden documented a pair of three-toed woodpeckers that immediately shifted their foraging to Scots pine trees that had been damaged by a prescribed burn. The fire apparently triggered a wound response in the pines that flooded the phloem with nutrients, and the birds exploited this within days.8Ornis Svecica. Phloem sap in fire-damaged Scots pine provides instant foraging opportunities for Three-toed Woodpeckers Picoides tridactylus The rapid behavioral switch suggests that woodpeckers are highly attuned to changes in tree chemistry and can detect freshly injured trees quickly.
Insects Under the Bark
When people think of animals stripping bark, they usually picture mammals or birds, but bark beetles and other wood-boring insects cause some of the most catastrophic bark damage on Earth. Bark beetles bore through the outer bark to reach the nutrient-rich cambium and phloem, where they lay eggs and feed. The larvae carve distinctive gallery patterns between the bark and the wood, and heavy infestations can loosen and kill large sheets of bark across an entire trunk. In temperate conifer forests, bark beetle outbreaks have killed millions of hectares of trees in recent decades, and a review of debarking insects noted that their populations have grown substantially, driven in part by warmer temperatures and drought stress that weaken trees’ chemical defenses.9Sustainable Forestry. Bark stripping insects (coleoptera: curculionidae) and climate change: Current issues and prospects in temperate forests
The relationship between bark beetles and trees is fundamentally different from that of mammals. A healthy conifer can often “pitch out” a small number of attacking beetles by flooding their entry holes with resin, but drought-stressed trees cannot mount this defense effectively. Once a tree’s resistance collapses, beetle populations explode, and the insects move to neighboring trees in a chain reaction. The result can be visible from satellite imagery: vast swaths of forest turning from green to red to grey over just two or three years.
How to Identify the Culprit
If you find stripped bark on a tree in your yard or woodlot, the pattern of damage usually points to the responsible animal. Here are the most reliable clues:
- Vertical strips with claw marks: Bear. The exposed wood often shows long, parallel scrape marks from teeth, and claw gouges may be visible on the bark above or beside the stripped area.
- Ragged upward-pulled strips: Deer or elk. The torn edges look fibrous, and the damage usually starts at a height the animal can reach while standing, typically below about 1.5 meters.
- Scattered tooth marks on branches or small trunks: Squirrels or porcupines. Squirrel damage tends to be patchy and concentrated on smooth-barked young trees, while porcupine damage often appears higher up and may fully encircle a branch.
- Hourglass gnaw pattern near the base: Beaver. Large wood chips on the ground confirm it.
- Neat rows of small holes: Sapsucker. The holes are roughly the diameter of a pencil and arranged in tidy horizontal lines.
- Bark flaking with sawdust underneath: Bark beetles. Peeling off a loose section reveals the winding galleries carved by larvae.
Location matters, too. Beaver damage occurs within a short distance of water. Bear damage in North America is concentrated in the Pacific Northwest and mountain forests. Elephant damage, of course, occurs only in African and Asian ranges. In the UK, grey squirrels are the first suspects for bark stripping on young hardwoods.
What Bark Loss Does to a Tree
Bark is not just an outer shell. It contains the phloem, which transports sugars produced in the leaves down to the roots, and it protects the cambium, the thin layer of dividing cells that produces new wood and new bark each year. When bark is stripped in a narrow vertical line, the tree can often heal by growing new bark over the wound from the edges. But when bark is removed in a ring around the entire trunk, a condition called girdling, the tree is in serious trouble.
Girdling severs the phloem, cutting off sugar transport to the roots. Research on citrus trees showed that girdling caused sugars and starch to accumulate above the wound while concentrations in the roots dropped sharply.10PubMed Central. Girdling affects carbohydrate-related gene expression in leaves, bark and roots of alternate-bearing citrus trees Starved of energy, roots begin to die. A study of girdled Scots pine found that cambial activity ceased below the wound after treatment. The following growing season, the cambium reactivated above the girdle but remained dormant below it, and the girdled trees eventually died.11Silva Fennica. The effect of stem girdling on xylem and phloem formation in Scots pine
Even partial bark removal invites secondary damage. Exposed sapwood dries out quickly and becomes a point of entry for fungal pathogens and wood-boring insects. In conifer plantations, bark-stripped trees frequently develop stain and decay fungi that degrade the timber, reducing the tree’s commercial value even if it survives. The Serengeti elephant study mentioned earlier found that repeated low-level bark damage was more lethal than a single severe stripping event, in part because each new wound reopened pathways for infection before the previous one had healed.3Journal of Ecology. Elephant damage, not fire or rainfall, explains mortality of overstorey trees in Serengeti
Why Bark Is Worth Eating
Bark stripping is overwhelmingly driven by nutrition. The phloem and cambium that lie just beneath the outer bark are among the most energy-dense tissues in a tree during the growing season. Phloem transports dissolved sugars, and cambium cells are packed with starches and proteins as they actively divide. For animals that can access these layers, bark represents a reliable, immobile food source that is available year-round in at least some form.
Seasonality matters a great deal. Bears, squirrels, and primates all concentrate their bark feeding during the months when the cambium is most active and the bark peels away most readily. In temperate forests, that window runs roughly from late spring through midsummer. Deer, by contrast, tend to strip bark in winter, when alternative forage is scarce and bark serves as a survival food rather than a preferred one. The difference in timing reflects different strategies: spring bark feeders are choosing bark because it is nutritionally rich at that moment, while winter bark feeders are resorting to it because almost everything else is gone.
Mineral content plays a role for some species. The primate research noted that eucalyptus bark may be sought specifically for its sodium, a mineral that can be hard to find in plant-based diets.7US EPA HERO. Primates bark-stripping trees in forest plantations – A review Porcupines in North America are also thought to target certain trees partly for their mineral content. And the three-toed woodpeckers in Sweden demonstrated that injury-induced chemical changes in bark can create sudden foraging opportunities, drawing animals to trees they previously ignored.8Ornis Svecica. Phloem sap in fire-damaged Scots pine provides instant foraging opportunities for Three-toed Woodpeckers Picoides tridactylus
Warming Temperatures and Shifting Damage Patterns
Climate change is reshaping bark-stripping dynamics from multiple angles. The most visible effect involves insects. Warmer winters allow bark beetle larvae to survive in areas that were previously too cold, while drought-weakened trees are less able to defend themselves with resin. The result has been massive conifer die-offs in the northern hemisphere, with bark beetles acting as the proximate cause of death in forests already stressed by heat and water shortage.9Sustainable Forestry. Bark stripping insects (coleoptera: curculionidae) and climate change: Current issues and prospects in temperate forests
Mammalian bark stripping may shift as well, though the pathways are less direct. Milder winters with less snow can reduce deer reliance on bark as emergency forage, but milder winters also support higher deer populations, which may increase total bark damage even if each individual animal strips less. Changes in tree growth rates affect phloem thickness, which in turn influences how attractive a tree is to squirrels and other phloem feeders. Plantation forestry may amplify these pressures: fast-growing monocultures produce exactly the thick, sugar-rich phloem that bark-stripping animals prefer, concentrated across thousands of hectares with no natural food alternatives nearby.
For forest managers and landowners, the practical upshot is that bark-stripping pressure is unlikely to diminish in the coming decades. Managing deer density, protecting high-value trees with physical guards, and maintaining diverse forest stands that give animals alternative food sources all reduce the risk. But the fundamental equation remains the same as it has always been: animals strip bark because the tissue beneath it is nutritious, accessible, and abundant, and wherever trees grow, something will eventually come along to exploit that resource.