250 million years ago, no tree existed that could have withstood temperatures below freezing. Either the tree’s “plumbing” would have frozen, or the leaves would have got frostbite.
So how did they do it? Trees accidentally prepared themselves for cold weather by adapting to drought conditions well before they started to spread beyond tropical climates. When trees work hard to get water from soil, sometimes their “pipes” suck in tiny pockets of air from surrounding tissue. This is bad, because for a tree to move water from its roots to its leaves, it relies on “capillary action” to force the water upward against gravity--basically, the air bubbles would cut into the chain of water molecules, and would shut off the taps. To fix this, trees evolved with skinnier pipes, which develop fewer bubble blockage problems. It’s also interesting to note that “capillary action” has a maximum height it can transport water against the pull of gravity: about 430 feet. This is why we don’t get trees taller than 430 feet!
Anyway, when trees started to spread to cold climates, they were already prepared for frozen pipes--keeping in mind that the ice itself doesn’t cause much harm. Actually, if you’ve ever walked by a tree and heard crackling or a gun-shot sound, that’s the tree’s pipes bursting. But a tree has thousands of these little pipes, so a few busted pipes doesn’t do a lot of damage. What IS harmful is when bubbles of gas that normally dissolve in liquid water end up forming in the ice. When the ice melts, the air bubbles remain, causing that same interruption of water movement.
But there’s still the problem of leaf frostbite. Think of how lettuce wilts and dies when it’s frozen: when the water in the living cells of leaves freezes, it forms sharp-edged ice crystals that puncture the cells. Trees had to learn to manufacture a biological version of anti-freeze, filling living leaf cells with concentrated sugary sap. Evergreens like spruce trees strictly use this technique, which is why they keep their needles year round! Deciduous trees like maples use a less concentrated formula, combined with the practice of losing leaves in the coldest months. As far as scientists know, the production of sugary sap is a tree’s only adaptation specifically for cold climates, which is why you’ve got to go north to tap for maple syrup!