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Southwest-facing Sides of Trees Have Most Stress in Winter

1-19-16 sun scald by Ginny P1000772A tree’s cells are normally dormant in the winter because of the cold temperatures, but the side of a tree trunk that faces the sun on a clear day can warm up enough that the cells become active. Even on a cold day, bark can warm to more than 50 degrees with direct sun on it. Once active, the cells are unable to return to dormancy by the time the sun goes down, which is when the temperature drops and can cause the active cells to die, resulting in what is referred to as sunscald. Dark bark can be a detriment to trees in winter, in that it absorbs rather than reflects the sun’s rays, thereby promoting the freeze-thaw-freeze cycle of cells.  This phenomenon occurs less frequently in forests, where the proximity of other trees offers some protection. (Photo by Virginia Barlow)
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11 responses

  1. Working with trees for over twenty years, I have a solution for this for property owners. As you say woodland trees do not suffer this problem of freeze thaw. You can put a board such as 2×4 (a length determined by the trunk), on the south side of your tree. You simply tie it there with cord or rope. This prevents the sun heating up the trunk to cause the thaw, therefore not causing the freeze which splits the trunk. I suggest here in Canada people put up their boards in November and remove them in April, after that you should have no problems.

    January 19, 2016 at 8:02 am

    • Wonderful! Thank you so much for sharing your expertise!

      January 19, 2016 at 9:20 am

    • Great solution, thanks!

      January 19, 2016 at 5:23 pm

  2. Al

    I wonder if this could be used to indicate direction on a cloudy day. I’ve found the “moss on the north side of the tree” thing to be true in a few areas of open woods down south, but haven’t found it of any use around here.

    January 19, 2016 at 8:29 am

  3. Kathie Fiveash

    Is the white bark of birches an adaptation to avoid sunscald? I know they are one of the most northerly hardwoods.

    January 19, 2016 at 8:52 am

    • I have read that very thing – that there are more light-bark trees in the north for that very reason. I don’t know if this is true, but your suggestion seems to have merit!

      January 19, 2016 at 9:22 am

  4. Great post on the subject of sunscald Mary as I have seen this condition on many trees most my life all around the New England area.
    Ginny provided an excellent example of this & I do hope her hand heals quickly after her wood splitting incident!
    Bill… WGF Studio53

    January 19, 2016 at 8:58 am

  5. I plant more sensitive nut and fruit trees on the north side of shorter evergreens or brush like dogwood so they get some shading during the winter.

    January 20, 2016 at 8:05 am

  6. Sigrin Newell

    When I am hiking in the woods, how do I tell sunscald from lightning damage? I can guess, but would like to know for sure.

    January 25, 2016 at 2:40 pm

    • I cannot answer that question, and will consult my forester/naturalist friend to find out!

      January 25, 2016 at 3:20 pm

      • Hi Sigrin,

        My forester friend said, “Sunscald would only be on parts of the tree exposed to the low sun, probably not up in the branches and only on the south or southwest side of the trunk.
        The lightning strikes i’ve seen do vary but sometimes splinters of wood are shot right off the tree; the damage tends to extend over a longer section of the tree. If damage occurred many years ago, it might be hard to tell.”

        January 25, 2016 at 7:44 pm

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