I am snowshoeing slowly through the deep snow of a forested hilltop in Enfield outside Ithaca, New York, following a circuitous path behind my dog and my husband, pondering the nature of trees and my understanding of them. Puffs of snow drift down occasionally, a woodpecker drills, and beech leaves tremble in a breeze that I cannot feel.
My daughter asked me a few weeks ago over lunch why trees don’t freeze in winter. She was thinking about cold hardiness. A special herb from the West Coast had arrived blackened, nearly dead, after transit through airports during the Polar Vortex. A grown woman now, Charlotte still asks questions with the same intensity she had as a child. Now, since becoming interested in mind-body therapies, herbalism, and shamanism, she has taken a great interest in all the life forms around her, educating me about some aspects of plant life of which I have been ignorant. I should have been able to answer her question in a snap.
Yes, back in 1979 I took Water Relations with Professor Roger Spanswick at Cornell as part of my PhD studies. I received an A in the course, which I was very proud about, because I had to shepherd two of us through the class. On January 9th I had delivered my first child and on January 20th or so I sat at 9 am MWF in a classroom in the basement of the Plant Science Building in the front row with Jack in a Snugli. Dr. Spanswick, always entirely gracious about Jack’s presence, often told me he would be happy if I took Jack out of the Snugli, implying that he was worried that Jack might be getting smothered. I dared not do so because Jack was a very active infant, except in the Snugli. I could feel his heart beating so I was not worried. (Jack and I successfully TAed Phycology, the study of algae, together that semester as well.) I want to make clear that Dr. Spanswick made Water Relations fascinating, his lectures were brilliant and comprehensive, and it is just the passage of time that has made retrieval of the pertinent information difficult.
The cold hardiness of trees in winter. The question lurked in my mind. Although I found one of my water relations textbooks, it dwelled solely on Plant and Soil Water Relationships (the title of the text), and did not include cold hardiness. Not surprisingly, one of my favorite magazines, Northern Woodlands, gave me good information. An article in the December 2013 issue, which I unaccountably missed, titled “ How Do Trees Survive Winter Cold” by Michael Snyder, forester and Commissioner of the Vermont Department of Forests, Parks, and Recreation, provides answers.
The basic facts are these. Trees are about 50% water so the danger of freezing in winter is great. Although many cells in a tree are dead, forming important structural elements, like bark, and these do freeze, there are important “tissues” of living cells that must not be allowed to freeze. A threefold system for minimizing the formation of ice crystals is in place: (1) the composition of the cellular membrane changes in order to force more water out of the cell; (2) the contents of the living cells become sweeter as starch is turned to sugar (“sweet antifreeze”); and (3) as a result of the first two changes, the remaining contents of the living cells go into a supercooled or “glass phase” (“suspended animation”) that disallows the formation of ice crystals in the interior of the cell, though ice crystals may form outside the cell.
Snyder says that not all the details of these processes are understood. Mystery and magic remain. The “magic” is that a tree survives winter as a community of living (nonfrozen) and dead (frozen) cells living side by side at the same temperature. Snyder cites research plant physiologist Paul Schaberg of the USDA Forest Service’s Aiken Forestry Sciences Laboratory in Burlington, Vermont, as a source of ongoing research.
I love trees in winter. I see their structure, the strength of the main trunks tapering to ever greater points of delicacy. I see their wounds. Almost every tree bears a sign of mutilation. The forest is a place of constant turmoil, losses and gains as trees must outgrow heavy grape vines, survive bark blights, deer antlers rubbing great gashes, and crashes caused by lightning. It’s only in winter when I see them “naked” that I understand so much more about their lives.
Trees in winter have become friends that I miss in summer when leafiness distracts my eye from the “inner” lives I have come to know during the cold. Our woods, about 10 acres on a hilltop on a piece of land we call Seven Fields, is a sugar maple-beech climax forest that includes white ash, black cherry, and red oaks in the upperstory, and hophornbeam, spice bush, and carpinus in the lower story. As I snowshoe through the forest in the deep cold, I think about disturbance and suspended animation, how the forest is a lesson in the splendid survival of life forms that cannot run away. I am thinking also of the questions we ask and how and why we ask them, and the answers we find and how and when we find them.
* I realize that encomium is a strange word in this context, but I wasn’t satisfied with “tribute” or “appreciation.” Encomium, a Latin word derived from a Greek one meaning “laudatory ode,” carries the sense of a eulogy. A few years ago the New York Times carried a headline on the front page, something like “Forests Dying Around the World.” A forest remnant of 10 acres deserves a big word.