Deer and Elk Damage to Trees in Western Montana

How do you know deer did it?

Browsing leaves a ragged edge. MSU Extension explains that mule deer and white-tailed deer lack upper incisors, so they cannot clip a twig. They twist and tear it, leaving a jagged or torn surface. Rabbits and rodents, by contrast, typically leave a clean cut at a 45-degree angle. Height is the other clue. MSU's MontGuide on deer damage notes that deer browse can occur up to six feet above the ground, and that line rises with the snowpack.

Rubbing looks different and is hard to mistake. MSU describes bark scraping and shredded bark as the evidence of antler rubbing: strips of bark hanging from a young trunk with bare wood showing underneath.

When does browsing and rubbing happen?

Rubbing has a season. According to MSU Extension, male deer rub on trees in the fall and early winter to remove velvet and to mark trees. Protection that goes on after the first snow is often too late.

Feeding is year-round, though MSU notes it is lighter in summer. Its MontGuide describes deer eating flowers and foliage during the growing season and feeding on tender buds and young plants in the fall and winter. University of Minnesota Extension gives the reason winter is hardest on trees: food shortages push deer and rodents onto bark, twigs and buds.

Which trees get hit hardest?

For rubbing, MSU is specific: deer prefer immature trees with smooth bark and no limbs, and it singles out aspen as a favorite. A newly planted shade tree with a clean, straight trunk fits that description exactly, which is why so many are damaged in their first few autumns.

For browsing, age matters more than species. MSU's MontGuide says younger, more tender and newly transplanted plants are damaged more significantly than larger, well-established ones, which can often withstand some feeding and fully recover. It also notes that well-fertilized trees and shrubs are more attractive to deer than unfertilized ones. The same publication ranks plants by resistance and is candid about the limits: deer-resistant does not mean deer-proof, and no plant is safe from a hungry deer. For species that suit this area, see the best trees to plant in western Montana.

Is elk damage different?

It is the same kind of injury on a larger scale. A U.S. Geological Survey study of three aspen stands in southwestern Montana found that stems from about 20 to 250 centimeters tall were browsed, and that stems 2 to 13 centimeters in diameter were preferentially selected for rubbing and gnawing. The researchers concluded that elk were primarily responsible. Dead saplings had twice the area of bark removed as live stems of similar size, which suggested that bark removal played a major role in killing them.

The study's recommendation is useful for anyone growing aspen in elk country: protect young stems until they reach about 13 centimeters in diameter, roughly five inches, and have grown out of the browse zone. That is a longer commitment than most people expect when they plant. Our guide to quaking aspen problems covers the rest of what goes wrong with that tree.

What protection actually works?

Physical barriers, sized to the job. For individual trees, MSU Extension's first recommendation is to install trunk guards or tree protectors on susceptible trees. An MSU Extension wildlife publication lists plastic tree wrap, mesh tubes and woven-wire cylinders for protecting young trees from browse and scrape damage, and says a four-foot-high woven-wire cylinder will usually keep deer from rubbing a trunk with their antlers.

For a garden or a group of trees, the same publication reports that research at Montana State University showed a six-foot fence is sufficient to keep deer out of a garden, and the MontGuide calls a permanent fence at least six feet high potentially cost-effective for backyard gardens with constant pressure. Other states go higher; University of Minnesota Extension recommends eight feet. MSU's advice is to concentrate fencing around the critical areas, such as high-value trees, so it encloses as small an area as possible. These figures are for deer. We did not find a Montana source giving a fence or cage height for elk, so for elk pressure ask your county MSU Extension office what has held up locally.

What about orchards and fruit trees?

Fruit trees have everything deer like: smooth young bark, tender shoots, buds at head height and fruit on the ground. MSU's MontGuide suggests electric fencing as a possible solution in orchards and around ornamentals, and describes vertical electric fences as effective under moderate to high deer pressure. It also notes they need weekly inspection and voltage checks, so they suit someone who is on the property regularly.

For a handful of backyard apples or pears, the woven-wire cylinders MSU describes can be made wide enough to keep the branches out of reach until the canopy grows above the browse line. Deer-torn shoots and broken branches can be cleaned up during fruit tree pruning in the dormant season.

Do repellents work?

Partly, and for a short time. MSU's MontGuide states that repellents typically only reduce damage, that even the most effective ones reduced browsing by about 60 percent, and that they work over short periods of one to two weeks before reapplication is needed. They are less effective on highly palatable plants and where deer have no alternative food. In the research MSU reviewed, the most effective products used putrescent whole egg solids, ammonium soaps of higher fatty acids, or capsaicin.

Two points from the same source are easy to miss. Repellents are legally classified as pesticides, so the product label is the law, and products used in Montana must be registered with the Montana Department of Agriculture. And repellents address feeding. MSU's guidance for antler rubbing is a physical guard.

Will a rubbed tree recover?

It depends on how much of the trunk's circumference lost its bark. The tissue just under the bark moves sugars from the leaves down to the roots. A rub that leaves a continuous strip of intact bark up the trunk keeps that connection alive, and the tree can grow new bark in from the edges over several years. A rub that removes bark all the way around girdles the tree. University of Minnesota Extension notes that animals can girdle and kill trees and shrubs this way, and the Montana elk study points the same direction.

For a partial wound, MSU Extension Forestry's advice on torn bark applies: trim loose bark back to where it is firmly attached and remove protruding splinters, taking care not to enlarge the wound, because a smooth surface lets new bark close over faster. The same fact sheet says pruning paint has not been shown to affect healing. Then water the tree through the next summers and put a guard on it before fall.

If a valued tree has been rubbed or heavily browsed, a tree health and risk assessment will tell you whether it is worth protecting or better replaced. We can also prune out the broken wood as part of our tree services. For related seasonal damage, the Montana Tree Guide includes a spring tree care checklist that covers voles and winter injury.

Call HJ Property Care & Tree Service at (406) 215-7319 or request a tree assessment and an ISA Certified Arborist will look at the tree with you.

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