Maple trees lose bark for reasons ranging from perfectly normal growth to serious disease, and figuring out which one you’re dealing with usually comes down to where the bark is coming off, what the exposed wood looks like, and what time of year you notice it. Some maples naturally shed outer bark as they grow, while others lose bark because of frost damage, fungal infection, boring insects, or hungry squirrels. The good news is that most bark loss on a mature maple is not an emergency, but some patterns do signal trouble worth addressing.
Normal Bark Shedding as a Maple Grows
Before assuming something is wrong, consider that many maple species shed bark as part of their normal aging process. Young maples tend to have smooth, tight bark. As the tree grows and the trunk expands, the outer bark can’t stretch to keep up. It cracks, flakes, and peels away to make room for new bark forming underneath. This process, called exfoliation, is especially visible on silver maples, red maples, and certain ornamental varieties bred specifically for their peeling bark. If you see thin strips or plates of bark coming off and the wood underneath looks healthy, smooth, and greenish or light-colored, you’re probably just watching your tree grow.
The telltale sign that bark shedding is normal is consistency. If bark is flaking or curling off in roughly even patches around the trunk and major limbs, and the tree otherwise looks vigorous with a full canopy, there’s nothing to fix. Trees that are growing quickly, particularly after a rainy season or a heavy fertilizer application, sometimes shed bark more dramatically than usual because the trunk is expanding faster. This can look alarming, but it’s the botanical equivalent of outgrowing your clothes.
Frost Cracks and Winter Sun Damage
If you notice vertical splits in the bark, often on the south or southwest side of the trunk, winter weather is a likely culprit. During cold, sunny days, direct sunlight warms the bark on one side of the tree enough to thaw the tissue underneath. When the sun drops or a cloud passes, the temperature plunges rapidly, and the thawed cells refreeze and burst. This cycle creates long vertical cracks that can open up bark and expose the wood beneath. The damage is sometimes called sunscald or southwest injury, and it’s one of the most common reasons homeowners notice bark peeling on younger maples in late winter or early spring.
Frost cracks tend to recur in the same spot year after year, widening slightly each time. Research on Norway maples planted in Michigan found that trees growing in low-lying or poorly drained areas developed frost cracks more frequently than trees on better-drained ground, and wrapping the trunks with Kraft paper in autumn did not reduce the cracking.1Arboriculture & Urban Forestry. Effect Of Tree Wrap On The Incidence Of Frost Crack In Norway Maple That finding surprised a lot of arborists at the time, since tree wraps had been a standard recommendation. Wraps may still help very young transplants get through their first couple of winters, but they’re not a reliable fix for frost cracking on established trees.
The bark along a frost crack often loosens and eventually falls off, leaving a visible scar. The tree will attempt to roll new bark over the wound, forming raised ridges called callus tissue along the crack’s edges. If the crack stays dry and the tree is otherwise healthy, it can wall off the damage over several years. The bigger concern is that open frost cracks create entry points for fungal pathogens and boring insects, which can cause more significant problems down the line.
Fungal Cankers
When bark loss is concentrated around a sunken, discolored, or oozing area on the trunk or a major branch, a fungal canker is worth suspecting. Cankers are localized infections where a pathogen kills the bark and the cambium layer underneath, causing the dead tissue to crack, peel, or fall away. Several fungi target maples specifically, and they tend to get in through wounds: a pruning cut, a lawnmower nick, or one of those frost cracks mentioned above.
One of the more destructive canker diseases in sugar maples is caused by the fungus Eutypella parasitica. When researchers dissected sugar maple trees bearing these cankers, they found significant internal decay extending well beyond what the surface damage suggested.2The Forestry Chronicle. Defect Associated with Eutypella Canker of Maple The cankers themselves look like elongated, slightly sunken patches where the bark has died and started falling off, sometimes with a target-like pattern of annual growth ridges around the wound as the tree tries and fails to close over the infection. The hidden rot inside the trunk is what makes Eutypella cankers particularly dangerous: a tree can look like it has a manageable surface wound while its structural integrity is compromised.
Other fungal cankers show up differently. Some produce dark, wet-looking stains on the bark that eventually crack open. Others cause the bark to blister and peel in sheets. What they have in common is that the bark loss isn’t uniform around the trunk. It’s concentrated around a visibly sick area, the exposed wood often looks discolored or wet rather than clean and light, and the tree may show dieback in the branches above the canker where water and nutrient flow has been cut off.
There’s no spray-on cure for most canker diseases once they’re established. The standard approach is to prune out infected branches well below the canker margin if the infection is on a limb. Trunk cankers on large trees are harder to manage and sometimes the best option is monitoring the tree’s overall health and planning for removal if it becomes structurally unsafe.
Boring Insects
Several insects tunnel into maple bark and the wood beneath it, leaving behind wounds that cause bark to crack, bulge, or slough off. The sugar maple borer is one of the more studied culprits. Its larvae chew a horizontal gallery under the bark during their first year, creating a horizontal scar. In the second year, the larva extends the gallery vertically, producing a more prominent vertical scar. The difference matters: research found that about one in five horizontal scars showed associated decay, while nearly three-quarters of vertical scars did.3Journal of Forestry. Decay Risk for Sugar Maple Borer Scars Vertical scars mean the insect stayed longer and did more damage, giving decay fungi a bigger foothold.
You can often spot borer activity before bark actually falls off. Look for small round exit holes, sawdust-like frass pushed out of the bark, or slightly raised or spongy areas where the bark over a gallery has loosened. On stressed or weakened trees, borer infestations can be severe enough to kill large patches of bark on the trunk. Healthy, vigorous maples are better at fighting off borers by flooding tunnels with sap, which is why maintaining overall tree health through proper watering and avoiding root damage is one of the better preventive strategies.
The Asian longhorned beetle is another borer that targets maples, though it’s an invasive species found in limited areas of the northeastern United States and parts of Canada. Its damage is more dramatic: large exit holes roughly the size of a pencil eraser and visible bark loss on upper branches and the trunk. If you suspect this pest, report it to your state’s agricultural department, because active eradication programs depend on early detection.
Squirrels and Other Animals
Sometimes the bark thief is a mammal, not a microbe. Gray squirrels strip bark from maple trees, particularly sugar maples, and they can do it aggressively. A long-running study of sugar maple bark stripping in a Minnesota forest found that in some winters, roughly 15 to 19 percent of the sugar maples had some bark removed by gray squirrels. Most of the damage occurred in the upper third of the tree, and branch wounds rarely affected more than a quarter of the leaf-bearing branches. Stem wounds were usually short, under about a foot long, though in one winter as many as 15 percent of injured trees had their stems completely girdled.4Journal of Forestry. A Six-Year Record of Sugar Maple Bark Stripping by Gray Squirrels in a Minnesota Oak-Maple Stand
Squirrels strip bark to get at the sweet, sap-rich cambium layer underneath, especially in late winter and early spring when other food is scarce. The damage tends to look ragged and torn rather than the clean splits you see from frost cracks, and you’ll sometimes find small tooth marks or bark shreds at the base of the tree. Deer can also rub bark off maples, especially young trees, when bucks scrape their antlers against trunks in autumn. Deer rubs are usually limited to a strip on one side of the trunk, a few feet off the ground.
Complete girdling, where bark is removed all the way around the trunk or a major branch, cuts off the flow of sugars from the canopy to the roots and will eventually kill the affected part of the tree. Partial girdling is something most healthy maples can survive, though the wound may take years to close over and leaves the tree vulnerable to secondary infection.
How to Read the Damage
With so many possible causes, it helps to have a mental checklist when you walk up to a maple that’s losing bark. The location, pattern, and appearance of the exposed wood all point you in different directions.
- Uniform flaking: Bark peeling in thin strips or plates evenly around the trunk, with healthy-looking wood underneath, is almost always normal growth.
- Vertical splits: Long cracks running up the trunk, especially on the south or southwest face, suggest frost cracking. Look for callus ridges along the edges of older cracks.
- Sunken patches: A depressed area where the bark is dead, sometimes with concentric ridges or discolored wood, points toward a canker infection.
- Small holes and sawdust: Round exit holes or frass on the bark surface indicate boring insects. Check whether the bark above and below the holes has loosened.
- Ragged tears high up: Shredded bark in the canopy with tooth marks at the edges is characteristic of squirrel activity, especially if it appears in late winter.
- One-sided scraping: A rubbed patch on one side of the trunk, two to four feet above the ground, is often deer antler damage.
The exposed wood itself tells you a lot. Bright, clean, greenish or cream-colored wood under peeling bark is a good sign. Dark, wet, soft, or foul-smelling wood under the bark means decay is already underway and the problem has been going on longer than the visible damage suggests.
When Bark Loss Threatens the Tree’s Survival
A maple can tolerate losing bark over a portion of its trunk without serious long-term consequences, as long as the remaining bark and cambium can still transport water and nutrients around the wound. The rough threshold most arborists use is that if more than about half the trunk’s circumference has lost bark at any single height, the tree’s ability to sustain itself is in jeopardy. Below that, the tree can often compartmentalize the damage and grow new tissue over the wound over several growing seasons.
What accelerates problems is layered stress. A tree with a frost crack that gets colonized by a canker fungus, which then attracts boring insects, is in a much worse position than a tree with just one of those issues. Drought stress, root compaction from nearby construction, and excessive pruning all weaken a maple’s ability to fight off bark-related problems. The single most effective thing you can do to protect a maple that’s losing bark is ensure it isn’t also dealing with water stress or root zone damage.
Practical Steps After You Spot Bark Loss
Resist the temptation to clean up a bark wound aggressively. The old advice to paint tree wounds with sealant or tar has been largely abandoned; research over the past few decades consistently showed that wound dressings don’t speed healing and can sometimes trap moisture against exposed wood, encouraging the very decay they were meant to prevent. A clean wound exposed to air will dry out and develop its own protective boundary faster than one sealed under a layer of paint.
If bark is hanging loosely, you can carefully trim back the dead bark to where it’s still firmly attached. Use a clean, sharp knife and cut along the living bark edge without digging into the green cambium layer. This tidies the wound margin and helps the tree form callus tissue more evenly. Don’t peel back bark that’s still partially attached and alive; you’ll enlarge the wound.
For canker-affected branches, prune well below the visible margin of dead bark, ideally at least a foot into healthy wood. Sterilize your tools between cuts to avoid spreading the pathogen. Trunk cankers on large trees generally can’t be pruned out without killing the tree, so the practical question becomes whether the tree is safe to keep standing. A certified arborist can assess internal decay with tools like a resistance drill or a mallet tap test and give you a realistic timeline for the tree’s structural safety.
Young maples that suffer frost cracks or sunscald in their first few years after planting may benefit from a light-colored tree guard on the south and west sides of the trunk during winter. This reflects sunlight and reduces the temperature swings that cause the damage. Remove the guard each spring, since leaving it on year-round traps moisture and can cause its own bark problems.
Bark Loss on Specific Maple Species
Not all maples handle bark loss the same way. Silver maples are notorious for shedding large flakes and strips of bark as they age, to the point where concerned homeowners call arborists every spring only to be told the tree is fine. Red maples shed bark less dramatically but still peel noticeably on older trunks. Japanese maples, by contrast, have thin bark that doesn’t shed much but is easily damaged by sunscald, and a small patch of bark loss on a Japanese maple trunk can be proportionally more serious because the trunk is so narrow.
Sugar maples are particularly susceptible to the combination of borer damage and canker disease described earlier. Their sap-rich cambium also makes them an attractive target for squirrels. Norway maples, widely planted as street trees across the northern United States, handle frost cracking and urban stress reasonably well but are prone to girdling roots at the base of the trunk, a condition where roots wrap around the trunk and slowly strangle the bark from below. If bark at the base of a Norway maple seems to be dying in a band that runs in a circle, dig gently around the root flare and look for a root pressing into the trunk. Cutting the offending root early can save years of decline.
Freeman maples, a hybrid between red and silver maples, combine traits of both parents. They grow quickly and can shed bark aggressively during growth spurts while also inheriting the silver maple’s tendency toward included bark in branch crotches. Included bark is where bark gets trapped between a branch and the trunk as both grow outward, creating a weak attachment. Eventually the branch may split away, ripping off a large section of trunk bark with it. Proper pruning of competing leaders while the tree is young is the best way to prevent this particular brand of bark loss.