How Do Deciduous Trees Go Through Winter

First chlorophyll breaks down and gets reabsorbed, allowing the other pigments to lend their colors to the foliage and turn it copper, red, yellow and orange. The tree sends a chemical called abscisic acid to the terminal buds, which shut down the flow of sap to the leaves, signaling them to break off the branches. After the leaves have fallen, the tree enters dormancy, a period during which it ceases growth, slows down its metabolism and lives off the energy stored in its roots as starch.

The starch sweetens the sap and the reduced amount of water increases its density, making it behave like antifreeze to protect cell walls from bursting. The walls also become more pliable to allow water to pass through them and fill the interstitial space, making up for changes in its volume.

The tree's dead cells, which during the warm months are used as vessels for sap circulation, can freeze during winter, when they are nearly empty, without harming the tree, and act like insulation to prevent damage to living cells. The sap changes its chemical composition and turns into a supercooled liquid which will stay viscous instead of creating ice crystals even at temperatures that go far below freezing.

Finally, trees get a lot of help from snow, wrapped like a blanket around their roots, to protect them from bitter chills.