Like little tails of little lambs, On leaf-less twigs my catkins swing;
They dingle-dangle merrily, Before the awakening of Spring.
While yet the woods lie grey and still I give my tidings: “Spring is near!”
One day the land will leap to life, With fairies calling: “Spring is HERE!”
The Song of the Hazel-Catkin Fairy – Cicely Mary Barker
To ward off the cold of winter, us humans bundle up with warm coats and hats, the birds puff out their feathers for thicker insulation and the animals grow a thick extra layer of downy fur.
I learned of an old homesteader woman in Armstrong years ago, who could always tell how bad the upcoming winter was going to be by just observing how fuzzy the caterpillars got in the fall, and apparently she was never wrong. So how do trees take on the terrible temperatures of winter?
A fun, animated YouTube video called, “How Do Trees Survive Winter,” explains how trees have adapted to cold climates since they rose up from the ground millions of years ago to a warm and tropical environment.
About 250 million years ago, there wasn’t a tree on earth designed to survive temperatures below freezing because they were all built for life in the frost-free tropics. If you took either an ancient or modern tropical tree and transported it to Siberia in winter, its water would freeze into sharp-edged ice crystals, fatally puncturing its living cells in all its leaves, which is the same thing that happens to lettuce and spinach when it freezes.
Cold weather also means that water in the tree’s plumbing system also freezes, and dangerous bubbles form in the ice from gases that were previously dissolved in the liquid water. The ice itself doesn’t cause much harm, but when it thaws, the bubbles remain, which is a problem because the whole plumbing system relies on the inter-molecular attraction of water molecules pulling each other upwards against gravity.
Air bubbles break the chain of molecules, essentially shutting off the flow of water.
So trees need to avoid two things – bubbles in their pipes and direct damage to living cells due to ice crystals.
The first problem is solved before ever leaving hot climates, because air bubbles are also a problem during drought. When plants work harder in drought to get water from the soil, their water-conducting pipes can accidentally suck in tiny pockets of air from the surrounding tissue. To combat this, trees in the dry tropics develop skinnier pipes, which – thanks to the counter-intuitive physics in water – develop fewer bubble blockages than the wide, high-capacity pipes of their wet tropical cousins.
So the plumbing of ancestral drought-adapted trees was accidentally pre-adapted to the cold, well before they began to spread from the tropics.
Upon arriving in cold places, trees had evolved two techniques to avoid frozen leaves. One is to fill living leaf cells with concentrated sugary sap – a biological version of antifreeze. Some trees, mostly conifers such as pines, fir and spruce, use solely this technique, leaving their needle-like leaves unfrozen year round with a super-strong antifreeze. Other species like maple, birch and larch, combine a less extreme level of sugar in their leaves, with the practice of going leafless during the winter to avoid foliar frostbite.
As far as we know, sugary sap remains the only adaptation that’s only useful in cold places, which is why you have to come to the north if you want to tap into the sweet antifreeze that might help you too to survive the winter.
We call that maple syrup, and it’s delicious!