The Beauty of Winter Trees: Tree Following, February 2016
I did not post about my red maple (Acer rubrum) tree in December or January. The busyness of the holiday season explains December, but in January I just couldn’t figure out what I wanted to say about the tree.
Like all deciduous trees in cold climates, my red maple goes into winter dormancy after it drops its leaves in the autumn. It’s tempting to think there is nothing going on with the tree during the winter months, but that is not true. The dormant tree is still an important presence in my life, and the first thing that strikes me about trees in winter is their stark beauty, especially when their limbs are limned in snow. The contrast of white snow on dark bark is striking and emphasizes the tree’s vertical shape.
We often talk about the visible winter form of a deciduous tree as its “skeleton,” but dormancy should not be confused with death. We can think of the winter dormancy of plants as more like sleep than like death, a restorative process that protects health. Part of the beauty of deciduous trees in winter is that they have a hidden life pointing us toward spring.
An attempt to learn more about the winter dormancy of trees led me to a Virginia Tech website on tree science. Here I learned that dormancy is a survival strategy that helps protect trees from the harsh environmental conditions of winter, enabling them to live long lives (hundreds of years long in some species). I also learned that there are stages of dormancy and that these stages are triggered by length of night and day and by environmental conditions like temperature.
As the nights got longer in fall, my tree entered the stage of “pre-dormancy,” when growth slows dramatically. This is when the tree’s leaves stop producing chlorophyll and the brilliant colors of fall foliage appear. By the time the tree enters true dormancy, it has dropped its leaves and stopped the growth of new shoots. Dormant shoots have “resting buds” that are covered in protective scales. Once the tree is in true dormancy, it won’t emerge from that dormancy until it has experienced a “period of prolonged chilling” (500-2000 accumulated hours of chilling, depending on the tree species and how far north it grows). As the days get longer in late winter, the tree enters the “post-dormancy” stage, when the resting bud is capable of growing but will not do so unless temperatures get warm enough. It is warm spring temperatures that will lead the tree to “break bud,” with flowers and new leaves.
Soon, I will be aware of subtle changes in the bare shoots of my maple tree that signal the transition to post-dormancy. In late February and early March, all the little shoots in the tree’s canopy will begin to swell with new life and the promise of spring.
Tree following is graciously hosted each month by Pat English at The Squirrel Basket. In her Cardiff, Wales location, trees have already broken dormancy and begun to bloom!
Jean's Garden 
as yours hibernate, ours aestivate. But our leafless stage is brief. Almost as if the fresh leaves push off the old ones. Missed my window to prune the fiddlewood while it was between leaves.
Diana, I had to look up the meaning of aestivate; thanks for improving my wood power! 🙂
The leafless stage here is definitely not brief; it is more than half the year. My tree lost its leaves in October and won’t grow new ones until May.
Interesting – and an elegant tree in the snow.
I am thinking our trees here don’t go truly dormant, as in recent winters we have hardly any icy weather at all. It’s scary to think a tree won’t wake up again unless it’s chilled for long enough first.
All the best 🙂
Pat, I think the need for a certain number of hours of chilling before a tree can come out of dormancy is an evolved protection against being tricked by unseasonably warm weather in winter. Here, for example, we usually have a warm spell in late January (called “the January thaw”) which is then followed by the coldest weather of the year. Trees that broke dormancy during that warm spell would probably be killed by the subsequent cold and therefore not reproduce, ensuring the survival of those that had a chilling threshold appropriate to their climate. (As I’m writing this in the late evening, the thermometer on my deck reads -15F, -26C.)
We have remarkably few dormant trees but perhaps that’s to be expected in our mild climate, where winter poses few hazards. We struggle to grow certain fruit trees (cherries, plums) precisely because they don’t get the chilling they need to enter dormancy and prepare for flowering. However, the few trees that do go dormant, even if briefly, always add some excitement to the garden when they emerge, as our ornamental pear tree (Pyrus calleryana) did this week, springing into bloom as if by magic!
Kris, The blooming of those fruit trees in early spring can be a magical moment. During the many years that I divided my time between Maine and Gettysburg, PA (on the Mason-Dixon line), I would often fly home to Maine for our “spring break” in March. I would leave Maine in the snow to go back and finish the semester; and often when I landed in the Baltimore-Washington area a few hours later, it would be to the sight of flowering pear trees.
Writing is hard work, we all have times when it is hard to find what we want to say…I’m glad you referenced the Virginia Tech site which I use as well as, if you are not using the University of British Columbia, and the University of Missouri sites you might find them useful as well..
Charlie, This was the first time I had stumbled upon the Virginia Tech site, which I will go to again. Thanks for the tip to check out the UBC and University of Missouri sites.
Hello Jean, I can’t figure out what combination of day-length, average temperatures, hours chilling and number of frosts trigger early spring plants to start flowering. Everything is almost a month early here. Daffodils are out in full force, the Camellias are open and even the Magnolias are beginning to emerge. It’s all very risky as we can still have hard frosts into early April.
Sunil, From what I read, I got the impression that these were very specific to local conditions. I am imagining that this is an evolutionary process in which plants that emerge from dormancy too soon (or too late?) don’t survive to reproduce. We are about to have our coldest night of the winter tonight, so I’m happy that my plants are in dormancy and that perennials are protected by several inches of insulating snow (although not the feet of insulation we had at this time last year).
I love dormant trees, they have such presence, even without the added beauty of snow. And I also love knowing that they are not, in fact, dead, but will soon spring in to life. I look forward to seeing the leaves unfurl on your maple in due course.
Janet, I love the stately presence of the dormant trees, too. Since I began following this tree when it was in bloom and about to get new leaves last May, I will probably be on to a new tree before this one gets leaves again. Although our latitude is south of yours, the cold temperatures mean that spring comes very late here.
The schedule for dormancy in Savannah is quite interesting. The live oaks have not yet lost their summer leaves. It is so peculiar.
Jayne, I wish I understood this whole process better. I wonder if trees as far south as Savannah don’t go into true dormancy but only a period of quietude of pre-dormancy that they can emerge from as soon as temperatures get warm enough to support new growth.
Interesting post! I love trees throughout the year, in all stages. Your acer with its snowy accent has a lovely form. I am not sure how many hours of dormancy our deciduous trees require. I doubt we get much more than 500 hours of chill hours, if that.
Deb, I found an interesting fact sheet from the Alabama Cooperative Extension Service (here) on chilling requirements for fruit trees in Alabama. They note that the chilling requirement is for hours at or below 45F, not at or below freezing.
Fascinating tree science. I love the dormancy of trees.
Donna, It’s a fascinating (if somewhat confusing) subject.
I thoroughly enjoy how you delve into a topic so you, and your readers, will better understand. An educator to the core. Thank you.
Joene, It’s true. 40+ years of teaching habits can’t be undone by a year or two of retirement. 🙂
Dormancy is more like sleep than death – very well put. The trees take their annual sleep through the months of winter unlike the nightly slumber of people.
*I hate WordPress. It wants me to log in. I don’t want to log in (I am admin for someone else’s website). So I changed my email and it ate my comment. Which was to say: I don’t love winter, so I have challenged myself to embrace it with my camera. I love trees at all times of year, but hardwoods in winter charm me especially. Leafless, they appear vulnerable, their limbs lifted in supplication to the sun to please come back to us!