Winter Bark Damage: Voles, Rabbits, and the Snow Line

Some of the worst damage a young Calgary tree suffers happens in February, under the snow, where nobody can see it. Voles tunnel along the ground beneath the snowpack and gnaw bark off the base of trunks, and rabbits stand on the crust and clip bark and branches at a height that looks oddly high once the snow melts.

By the time you find it in April, the damage is done. Protection is cheap, takes ten minutes per tree, and has to go on before the snow arrives.

Telling Vole Damage From Rabbit Damage

Voles work at ground level and below the snow line. Their damage is a band of gnawed, stripped bark right at the base, often hidden under grass or mulch, with fine parallel tooth marks a couple of millimetres wide and an irregular ragged edge.

Rabbits leave a much cleaner cut. They clip twigs and small branches at a distinct 45-degree angle, as if snipped with pruners, and they strip bark in patches higher up the trunk, up to the height they could reach standing on snow, which in a deep winter can be surprisingly high.

Why It Can Kill a Tree

The living tissue that moves sugars from the leaves to the roots sits just under the bark. Strip a patch and the tree can usually work around it. Strip a complete ring around the trunk and the tree is girdled, with no path left between canopy and roots.

A fully girdled young tree will often leaf out in spring on stored energy and then die that summer or the next, which is why the cause gets missed. Partial damage, up to about half the circumference, is usually survivable with good care.

Protecting the Trunk

For rabbits, a cylinder of hardware cloth or plastic mesh around the trunk works well, held a few centimetres away from the bark and tall enough to clear the expected snow depth. Remember that the effective height rises with the snowpack, so measure generously.

For voles, a spiral plastic guard or mesh pushed down to soil level closes the gap at the base. Pull mulch back from the trunk before winter, because deep mulch piled against bark is exactly the sheltered runway voles want.

Managing the Habitat

Voles need cover. Long grass left over winter, deep mulch against trunks, brush piles, and dense groundcover near young trees all create the protected runways they travel in. Mowing the grass short in late fall around young trees makes the area much less attractive.

Clean up fallen fruit and remove brush piles from near the orchard or the young plantings. Reducing shelter does more over a winter than any repellent.

Checking and Removing Guards

Guards need to come off, or at least be inspected, each spring. Left on year-round, they trap moisture against bark, hide insects, and eventually constrict a trunk that is growing.

Make it part of spring cleanup: walk the yard, pull the guards, look at the bark underneath, and note anything that needs attention before the growing season gets going.

If You Find Damage in Spring

Do not paint, seal, or wrap the wound. Clean cuts of loose bark are unnecessary. What the tree needs is support: deep watering through the season, mulch over the root zone, and no fertilizer pushing growth it cannot supply.

If the damage rings more than half the trunk, plan for the possibility of losing the tree and consider a replacement. Aardvark Tree Care can assess winter bark damage across Calgary and tell you whether a young tree is worth nursing along or better replaced now.

Rabbits cut at a clean 45 degrees; voles leave a ragged stripped band right at the snow line.