Winter can be a tough time for trees, and many varieties must shed their leaves for the cold months between fall and spring. Evergreens, on the other hand, have leaves on their branches during every season. Evergreens do lose their leaves, but not all at once like many trees that become bare; they gradually replace their leaves year round.
Trees that lose their leaves during the months of winter are called deciduous. Deciduous trees drop their leaves through a process called abscission. When it is time to shed the leaves, the trees produce a chemical called ABA, or abscisic acid, at the spot where the stem meets the leaf. The tree removes nitrogen and carbon from the leaves before they are released and stores them in the roots and inner bark. The nitrogen and carbon are stored as proteins, which will assist in the growth of new leaves the following spring. Shedding leaves helps the deciduous trees save water and energy, which would otherwise go to maintaining the leaves.
Similar to animals, trees also go into a hibernation-like state called dormancy. All of the trees natural processes slow down, including energy consumption, metabolism, and growth. Stalling growth saves lots of energy for the tree. Since the trees are not producing any food during the winter, they don’t need their leaves.
Evergreens also naturally promote the growth of other evergreens. Evergreen leafs and needles have a high carbon-nitrogen ratio, which makes the surrounding soil highly acidic. Evergreens have adapted to surviving in soil that has low nutrient levels, and low nutrient soil favors the growth of evergreens over that of deciduous trees. Additionally, the shade and shelter that evergreens create give younger evergreens a better chance to survive adversity, such as cold weather or drought.
Another danger to trees comes from snow and ice weighing down branches. Trees can receive damaged from having their branches pulled down from long periods of time. Certain evergreens, such as firs and spruces, have more flexible wood than other deciduous trees. This allows those trees to bend further with less of a risk of breaking.