Arboreal Rx: From beaver bites to boring beetles, our experts diagnose what ails your cottage trees

by Jo Currie

No doubt about it, cottagers love their trees – and no wonder. Their shade is refuge from the sun. Their trunks and limbs are home to hosts of our favourite fellow creatures. Their distinctive silhouettes welcome us back to the cottage when we’ve been away. And in the fall, their brilliant colours blaze along the shoreline. Because we love them, we hate to see them stressed or sick. After getting so many questions from cottagers worried about the health of their trees, we assigned a few “tree doctors” to the case. The result is this special Q&A feature, with the answers to your cottage tree questions. 

 

Originally published in the June 2005 issue of Cottage Life.

Question:

Some animal has stripped the bark off several birches along our shoreline. The damage starts about 30 cm above the waterline and is about 20–45 cm wide. These trees are at least 20 cm in diameter, and we thought they were large enough to be safe from beaver. Has some other animal, such as a porcupine, done this? Will the trees recover?

—Jennifer Wiber, Pickering, Ont.

From the location of these injuries, our experts are placing their bets on beaver. While porcupines can, and do, climb into trees to stay safe from predators while feeding off the bark and twigs, beavers remain grounded. Typically, their gnaw marks are 25– 45 cm high.

Your 20-cm trees aren’t big enough to be safe from beavers. They’ll tackle trees of almost any size, for a few reasons: to topple them and get at the more succulent twigs and bark of the upper branches; to help build their dams; and (last but not least) because their large, sharp incisors – which grow continuously – can overgrow their jaws if they’re not constantly wearing them down.

As for recovery, any wound leaves a tree vulnerable to attack by insects and disease. These trees will already have begun the process of sealing off their injuries. Their success depends on their overall health and vigour.

Question:

Most of the tamaracks at my Hills Lake cottage appear sick. I noticed it to a lesser degree last summer and assumed the problem was lack of rain. My young 60-cm saplings are suffering as badly as the mature trees. Is there a disease or insect that may be causing this?

—Mark Summers, Plevna, Ont.

There are several possible culprits, and the odds are they are working in combination to produce the browned foliage and tip dieback your photo shows. For a start, notes Alan Watson, director of The Arboretum at the University of Guelph, in a very dry period such as you experienced last summer, it’s likely many of the trees’ small rootlets would die. Much of the effect on the tree would be delayed until the following year when (no matter how generous the rainfall) the trees, with their reduced root capacity, would have difficulty taking up enough water and nutrients to thrive.

Additionally, for the past six years or so, Ontario has been experiencing outbreaks of larch casebearer (Coleophora laricella). Most of the damage occurs in late April and early May when the larvae feed on the needles, causing defoliation that, if extensive, can seriously weaken the tree. In turn, the tree becomes vulnerable to attack by another pest of tamarack,the larch beetle (Dendroctonus simplex).

If you’re feeling that nature is ganging up unfairly on your tamaracks, take heart – the trees normally recover from a casebearer attack by putting out a fresh set of leaves. And after examining the photo you sent, Dan Rowlinson, a forest health technician with the Forest Research Institute in Sault Ste. Marie, speculated that this tree, at least, looks likely to survive.

Question:

Last summer at our island on Lake Temagami, we discovered a 1.5-metre-long crack in one of our very tall red pines, starting from the ground up. Sap is coming out near the top, and there are large black ants in the split around the base. Is there anything we can do to extend its life?

—Judy Lee, Lake Temagami, Ont.

If it’s very tall, your pine is already a senior citizen. It has a natural lifespan and becomes more vulnerable as it ages. The split, or stress crack, could have happened in a big windstorm. But long before that, internal attacks from a variety of busy wood-decay fungi will have been gradually hollowing out the lower trunk, or butt, and weakening its structure. Your ants sound like carpenter ants, attracted to the moist, soft decayed wood inside, which is easy for them to excavate. The sap and the ants are just symptoms, though. An arborist might decide to drill through the trunk and insert a bracing rod, with washers at either end, to help hold it together. But with internal rot and a big split, this is really just a temporary solution. The tree is past its prime and our experts agreed that probably your best option is to leave it alone. Since the most vital part of the tree is its sapwood – the wood nearest the bark – it could live for a while yet, perhaps as long as 30 years. Or it could blow down in the next big windstorm. Only you can decide whether it’s a danger to buildings, power lines, or people. If it’s not, let it stand. Dead or alive, upright or on the ground, a large old tree is food and habitat for a wide variety of desirable critters, and you’ll have the pleasure of seeing them go about their business. And consider some advice from forestry consultant King Wright of King’s Forestry Service: If most of your pines are mature, plant some shade-tolerant young ones to replace them – the sooner the better. >>

Question:

There’s a rusty hook embedded in the trunk of our maple that looks like it once held a hammock. The tree has almost grown over it. Should we try to remove it? Can I use the tree to hang my own hammock?

—Vanessa Wade, Tichborne, Ont.

Leave it alone, say the experts. The maple has long since dealt with the small puncture that was made when the hook was inserted, by sealing off the area from the rest of the tree. To get the hook out, you’d have to make a bigger wound, doing more damage and potentially exposing the tree to infection before it can seal the site off again. Arborist Steven Mann, with Bartlett Tree Experts in Bracebridge, Ont., has often found sugar maples with forgotten embedded spigots. Such minor wounds are not usually a problem for a healthy tree to handle.Mann adds that you could attach your hammock the same way, with a single hook or ring. (Stainless- or galvanized-steel hooks make a cleaner puncture for the tree to deal with, and last longer.) Unless you can remember to remove it at summer’s end, never encircle the trunk with a rope or cable. As the tree grows in diameter such restricting bands will girdle and kill it. That said, some experts would suggest you avoid hanging a hammock there at all, as the healthiest tree is the one left alone. Consider buying a hammock on a stand, so you can move it around and enjoy your summer naps guilt free.

Question:

After a spring storm, we found that a large limb had broken off one of our big old oak trees. The tree seems to be fine except for that ragged piece sticking out from the trunk. Should we trim it off? Is there anything we should do to help the wound heal?

—Rebecca Egan, Sand Lake, Ont.

If the limb was alive when it broke, you’ll see fresh, moist wood at the wound site, and sap may be leaking out. You should trim off this ragged part in order to create a clean wound that’s harder for disease vectors to enter. Prune it back to the parent trunk, to the outside of the “branch collar,” or shoulder, where the branch thickens just before it joins the main trunk. Here, the cells divide rapidly, explains Bartlett’s Steven Mann, allowing the tree to begin sealing off the wound. A wounded tree doesn’t need a painted-on sealing product, which may even interfere with the tree’s natural process.

Whereas our bodies normally deal with a broken limb by repairing the damage – eventually allowing the wounded part to function normally – trees deal with wounds by sealing off the damage. Cells surrounding the wound change chemically and physically, isolating the injury from the rest of the tree. A vigorous tree is thus capable of overcoming very serious damage, but the isolated part – whether it’s a section of root, part of the main trunk, or a big limb – is no longer of any use to the tree.

If, on the other hand, the limb was long dead, the tree will have sealed off the wound already, so trimming the stump is mostly a matter of aesthetics. Just trim it up neatly, removing only the dead part and cutting no closer than the collar, about 7–10 cm from the trunk.

Question:

Our young white pine, which had seemed healthy and vigorous, died quickly last summer. There were no outward signs of damage. When we cut it down, I noticed this black discoloration in the trunk. Is this the cause of the tree’s demise? Do we have to worry about all the other white pines on our property?

—Peter Helston, Loon Lake, Ont.

The blackish discoloration is almost certainly one of the so-called stain fungi, probably introduced into the wood by a bark or ambrosia beetle. The beetles (and their larvae) cause damage by feeding on the inner bark, or cambium layer, of the tree. The stain fungus contributes to the damage by plugging up the phloem, the system of conduits that convey sugars and starches (made in the leaves) back to the rest of the tree.

That said, forest pathologist John McLaughlin, with the Ontario Forest Research Institute in Sault Ste. Marie, doubts these pests are the primary problem. These beetles are consummate opportunists, able to identify stressed trees and single them out for attack. He can’t tell from the picture (below) what would have caused this tree’s initial decline and left it vulnerable – but if the rest of your white pines remain uninjured and growing in a suitable environment, there’s no reason to suppose that they will suffer the same fate. 

 

Published in the June 2005 issue of Cottage Life magazine.

Copyright © 2005 by Cottage Life. All rights reserved. Reproduction of any article, photograph, or artwork, for other than personal use, in whole or in part, without the written permission of the publisher is strictly forbidden.