Some bear species eat trees, especially black bears and brown bears, which often scratch and peel at the bark of trees to get to the soft inner flesh of the wood.
One bear can peel the bark from up to 70 trees per day, causing significant damage to the health of trees and the economic value of timber!
After coming out of hibernation, black bears can’t find as much food as they need. So, they resort to trees that produce carbohydrates in early spring.
They peel them off to get to the new wood formed underneath known as sapwood, notes the USDA Forest Service.
These bears also “frill” the trees; they loosen the bark layers at the base and pull it up, away from the tree. Sometimes, the strips may hang from more than five meters, depending on the tree.
Black bears will also rub their shoulders, neck, and crown and may claw and bite trees when leaving their scent. This behavior is usually done by the males in the mating season.
Do Bears Eat Tree Stumps?
Bears often eat tree stumps if they can’t find enough food before hibernation. Black bears sometimes tear logs in late autumn and consume them when they’re trying to gain as much as weight possible prior to hibernation. Insufficient food in the winter is one of the major reasons why bears hibernate.
However, this isn’t the only period during which bears peel and eat trees. After hibernation, their food sources are still unavailable so they reach for trees. Trees produce sugars and carbs during early spring and bears will strip the bark to get to the sapwood underneath.
Bears also eat trees that are low in terpenes.
Oftentimes, a bear may taste a tree early in spring and then come several weeks after and peel the bark, probably when the sugar amount is higher. They strip the bark from trees using their sharp claws and consume the sapwood by scraping it off from the older wood using their teeth.
If there’s bark strewn at the bottom of the tree and vertical marks on trees and tree stumps from teeth, it may indicate bear activity.
Some peeled strips by a bear can hang for more than five meters like on the western red cedar tree. The North American Bear Center notes that broken branches are also a common food source for bears.
Some bears such as black bears are excellent tree climbers and can climb and bite off branches and then eat them when they come down. They will also pull and crash branches to consume the fruit which grows on them.
Here’s how easy it is for a massive grizzly to destroy a spruce tree:
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What Are the Marks that Bears Leave on Trees?
The marks bears leave on trees may be from bears eating the trees or bark, or from rubbing their backs on the trees. Brown and black bears turn their back on the tree and scratch it as if they have an itchy back. The marks they leave are for communication and territory marking.
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Both sexes rub their scent (each bear has a unique scent), but especially the males, before or after the mating season. They claw or bite trees around half a meter to two meters above the ground.
Interestingly, according to a study done by the University of Alberta, brown bears that rub against trees were found to have more offspring and more mating partners. The odors they leave behind reveal information for other bears like what they are, what position they’re in, and whether they’re related or not.
The researchers note that bears that are in good condition rub more vigorously and this may contribute to their reproductive success. The study also discovered that the rubbing helps the female bears with cubs to stay away from big males and prevent infanticide.
This video shows two grizzly bears vigorously rubbing against a tree:
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What Is the Extent of the Tree Damage Caused by Bears?
When entire tree girdling is done by bears, it’s fatal for the overall health of the tree. Partial girdling is also bad: it decreases the tree’s rates of growth and creates breeding grounds for insects and elevates the risk of diseases.
When bears come out of hibernation, they need food sources which are scarce at that period. Trees seem like a suitable option for them because they’re breaking from dormancy and starting to produce carbohydrates.
At this period, bears usually girdle Douglas Fir (Pseudotsuga menziesii) trees and even strip the entire bark to get to the sapwood which they scrape off the heartwood using their teeth.
Considering that a single bear can peel up to 70 trees per day, this behavior has a huge negative impact on tree health and their economic value.
The species of trees damaged by bears depend on the location. Douglas fir and western hemlock are the preferred option for bears in the Pacific and Grays Harbor counties. They also damage and consume Sitka spruce, western red cedar, red alder, and black cottonwood.
From an economic point of view, bears choose the most abundant trees, with the most productivity and the damage often happens prior to implementing preventive measures like thinning and fertilizer application.
This additionally increases the financial losses due to the prolonged period of time (20+ years) needed to restore trees to their pre-damage state.
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Bears often eat sapwood that’s underneath the bark of trees. They use their claws and teeth to peel trees’ bark to get to the sapwood which supplies them with carbs.
Bears do this before hibernation when they need extra calories or after hibernation when their preferred food sources are still unavailable.
They may also damage trees when rubbing vigorously against them to leave their scent. Some bears can cause extensive damage to trees which will result in the tree getting ill and eventually dying.
The trees they usually damage depend on the location, but some of the most common species are douglas-fir, western hemlock, and western red cedar.
Stuart is the editor of Fauna Facts. He edits our writers’ work as well as contributing his own content. Stuart is passionate about sustainable farming and animal welfare and has written extensively on cows and geese for the site.