January — Cracking trees and other scary winter tales

by Tom Lewanski

Warm days and freezing nights are tough on such thin-barked trees as maples.

Image courtesy of USDA Forest Service

After what has become known as the “winter finch incident”*, I proceed with some trepidation with this month’s installment. However, we intrepid phenologists always move forward, torpedoes be damned...

A couple of years ago, I noticed a portion of the bark on a maple in my yard was peeling off. Over the subsequent years a bare patch has developed and, upon closer examination, I noticed tiny round holes in the exposed wood. After spending many nights on stakeout, trying to observe the druids who have obviously been using this tree for some sort of ritual, I have learned that there is a very simple explanation for this phenomenon (going public with my embarrassments is good for me, according to my therapists). Anyway, getting back to the tree, instead of suffering from some kind of arboreal voodoo doll ritual, this maple is the victim of...wait for it . . . . . . sunscald. Yes, dear and faithful phenologists: sunscald.

On sunny winter days, with the sun’s energy bouncing off the snow onto the bark, the south side of the tree can actually warm into the 50s and 60s. Now, I am pretty certain that the tree does not actually think, but if it could it would be thinking “Woo hoo, get ready sap because spring is here. My butt is still pretty chilly but my front is feeling fine.” However, the sickness of the joke becomes apparent as the sun sets and the tree’s temperature falls back below freezing. This refreezing can be lethal, at least for the part of the tree that has warmed considerably and then refrozen in a short period of time. These conditions can cause the bark to die and/or a frost crack to form.

This dead portion of the tree provides easy access to disease, fungus, insects and other nefarious creepy crawlies. This is what happened to my poor little ‘ol maple. Those little aforementioned holes in my tree were made by wood-boring beetles. Young maples are prone to this kind of injury because they have relatively thin bark (*much like some of my colleagues who did not enjoy last month’s winter finch article, but I will not hold a grudge). To help prevent such injuries, remember always wrap your trunk! Now you know.

There are additional winter injuries that trees of all makes and models suffer through up here in the northland. Lest some of you think that I am once again making stuff up, the University of Minnesota Extension Service has a webpage devoted to winter tree injuries.

Till next month,

Peace Out!