Cambium Munchers – techniques for protecting trees from rodents

It’s been a steep learning curve the past few years as I’ve discovered just how much rodents love to chew the bark of young fruit trees. I’ve had to cut down, re-graft, bridge-graft (trunk bypass surgery), or give up on trees altogether due to winter rodent damage. I hope to spare you the same experience by sharing my own.

What ate my tree!?

Trees take the energy they collect through photosynthesis in the growing season, and store it as carbohydrates in their roots, trunk, and branches over winter. Just under the bark of your trees is the cambium, a thin layer of the tree’s trunk that is packed full of nutrients, minerals, and sugars. Think of how delicious maple syrup is. That’s how I imagine voles, mice, and rabbits feel about the trunks of young fruit trees.

Apple tree, chewed 3/4 of the way around by mice. Hopefully the remaining cambium is enough to support the tree and keep it alive.

Under the snow during winter, or in the protection of tall grass during the growing season, rodents will tunnel between trees and chew the cambium at the bottom of the trunk. If you live somewhere with snowshoe hares, rabbits, beavers, or porcupines, they will often walk on top of the snow and chew the bark above snowline. If they chew the full circumference of your trunk it is known as girdling, and the odds are the top portion of your tree will die. Often trees will re-sprout from below the girdle, but sometimes this will kill your tree altogether, especially if it happens repeatedly. Cambium is the actively growing vascular system of the tree, pumping essential fluid nutrients between the branches and roots. Keeping that cambium intact and protected is vital for producing a healthy tree.

Physical Barriers

Plastic coils: easy and convenient, but have some downsides

I have been and am still experimenting with different ways to protect young trunks from the teeth of rodents. There are lots of types of trunk protection tubes you can purchase, some better than others. Plastic trunk collars are easy to use, but are costly if you have a lot of trees to do. A determined rodent can also chew through plastic. Many models, such as the white coils pictured, need to be removed as the tree grows to prevent the tube from girdling the tree. They also provide a sheltered space for trunk borers and other insects in the summer, so if your trees are susceptible to this, you’ll need to take them off seasonally to visually monitor trunk for pests. Keeping these issues in mind, if you need something quick and easy, if a bit costly, plastic guards are a decent option.

Wire mesh trunk tubes are a cheap, simple, effective DIY alternative to plastic or purchased collars. In trials last winter, they were more effective than manufactured tubes as they could be left on during the growing season and mice did not chew through them. All new trees in our orchard are getting these this fall. Here’s how to make them:

  • Using 1/4″ hardware cloth or steel window screening, cut a piece that is at least 2-3 times the circumference of the trunk wide, by the height of your average snowpack. For my 2-5 year old trees and location, that is usually 8-12″ wide by 18″ tall.
  • Window screening is easier to work with, so I use it on dense beds of young trees. But hardware cloth is more durable, and the way to go for long-term orchard plantings.
  • If you have rabbits, hares, beavers, or porcupines, you’ll want to go at least 18″ HIGHER than the top of your snowpack to give full protection. You can reduce this height if you regularly snowshoe around your trees (more on this below)
  • Wrap your mesh around a piece of wood of similar size to your tree trunk – tool handles work great
  • Uncoil mesh and re-wrap around your tree. Tighten coil so that it wraps 1.5x or more all the way around. Check to ensure sharp edges of wire won’t impale or scratch the trunk.
  • Make sure bottom of coil is 1″ or more below the soil line. Mound mulch around outside of tube to prevent diggers.
  • Fasten with wire to hold in place.

The great thing about this system is that you can leave it in place year round, as it provides decent air circulation and you are able to see through it to monitor the trunk for pests. Just make sure grasses and weeds don’t invade that area. As the tree grows you can unfasten and expand the coil, and get many years of trunk protection.

I have many beds of young nursery trees that I will be experimenting with perimeter rodent fencing this winter, rather than individual trunk wrapping. I will hopefully find some systems that are less work to install for dense plantings and applicable to rows of berries. I’ll share those results when I have them!

Environmental Controls

Knowing what cambium munchers like to call home is one step towards reducing their damage. Like all animals, food and shelter are key.

HABITAT – Reducing shelter by cutting back tall grass, removing brush and preventing nesting areas such as wood piles will help keep rodents away from your trees. Avoid mulching trees with loose materials such as straw, cut grasses, or airy piles of leaves, as those make for great bedding and easy burrowing. Go for wood chip mulch around trees over winter whenever possible. I’ve heard of one orchard having success with planting garlic around the trunks of their trees and that really helping deter voles. I’ll be trying this in future years!

Snowshoes – an essential tool for vole tunnel management

REMOVE WINTER SHELTER – After heavy snowfall or when temperatures are just above freezing, I snowshoe around each tree in the orchard to collapse underground vole tunnels and create a hardpan of snow that is harder to burrow through. This also helps reduce height of snowpack so rabbits, beavers, and porcupines won’t chew as high and your trunk guards don’t need to be as tall. I do this around overwintering root crops as well, to reduce under-snow traffic. It’s a pretty fun winter chore and makes some wacky patterns in the snow.

Our stealth cat, Misty, makes a huge difference in keeping rodent populations under control

PREDATORS – Get a cat, make piles of rocks throughout your orchard to encourage snakes, put tall posts throughout young plantings as place for owls and hawks to survey and hunt, welcome coyotes, or get a trained rodent-hunting dog (it’s on my to-do list). Create an environment that encourages higher trophic levels to move in.

REDUCE FOOD ATTRACTANTS – If you have chickens or livestock near your orchard, make sure their feed is secured and not creating an attractant. Tall grasses going to seed in late summer also boost their numbers, so reducing food sources earlier in the season helps keep winter population down.

Willows and dogwoods are easy to coppice in the fall to provide a winter food decoy. Their bark is often stripped clean by spring, taking the pressure off your berries and trees.

PROVIDE ALTERNATE FOOD SOURCES – Collect small-diametre branches and prunings and pile them in the pathways so rodents chew on those rather than your trees. Fresh fruit tree prunings, willows and dogwood boughs are especially good decoys as their soft, sweet bark is appealing to rodents. I often do this between rows of berries, as it’s harder to protect their numerous trunks and low branches. You can then snowshoe the very edges of the pathways to make the rodents stay away from the beds. This principle can be applied to plantings as well – plant more trees than you need, or plant a sacrificial woody crop such as coppiced hazelnut, mulberry, or willow in between the trees you want to protect.

Prevention now = more fruit later

This Asian Pear was girdled two winters in a row, and had to be cut back to the ground each time. Luckily this was above the graft union, so it didn’t need to be regrafted. It miraculously has survived and is now eight feet tall. It’s getting permanent mesh tubes this fall, and hopefully will live a long productive life with no more vole damage.

Rodents, rabbits, and small grazers are a part of healthy ecosystems. Having a biodiverse, ecological orchard often leads to some amount of them. They play many services in the system and don’t need to be an enemy. Creating physical barriers around plants you want to protect, and working to keep rodent populations in balance will help reduce the loss of valuable trees. I know how heartbreaking it is to assess your trees after snow melt and discover girdled trees. I hope you don’t have to experience that. Like most things, prevention is everything.

Best of luck this fall with protecting your young plantings!

One comment

  1. What a gift Kim. The comprehensive and complex aspects you share are really “permaculture” at its best. You must come over for a cuppa and maybe with kids and a toboggan when the fall rush slows down. Your Linnae farm and other background has served you really well. I’m really glad you’ve moved here!

    Like

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