How Do Conifers Remain “Evergreen” During the Winter?

evergreen tree

Written by: Karlee May, Digital Media Coordinator

As we learned in a previous blog post, deciduous trees drop their leaves to prepare for winter. Why do conifers keep their needles? How are the trees “evergreen” even in the coldest winters? All leaves have stomata: pore-like structures that absorb light and carbon dioxide. The stomata are larger in deciduous leaves for action paced photosynthesis in the sunnier months. A deciduous leaf binges on sunlight at a fast, efficient rate.

Broad leaf trees and conifers share a similar trait: both broad leaves and conifer leaves are covered in stoma. Stomata are pores in leaves that allows the exchange of gases between the internal organism and the outside environment. Stomata inhale and exhale carbon dioxide, oxygen, and water vapour. Leaves in deciduous trees have larger stomata than the thin needle-like leaves of conifers.

Broad leaf trees use abscission to cut off the water supply to the leaves, resulting in the end of chlorophyll production. The leaves then die and fall off. To conserve energy over the winter, the trees store energy from photosynthesis in the roots and within the tree. The leaves of a broad leaf tree must fall off to conserve the water supply. Abscission prevents water from escaping and freezing.

evergreen branches

Unlike broad leaf trees, the leaves on conifers are thin and needle-like, and the stomata are small in contrast to the stomata of a broad leaf. Since the stomata in conifers are tighter and smaller, the rate of photosynthesis is reduced, but photosynthesis continues all year round. Tight and tiny stomata means that water loss is greatly reduced. The leaves do indeed fall off, but it occurs at a continuous rate instead of falling off all at once. The large pores in broad leaves means water can escape and endanger the life of the tree: so, the deciduous trees must drop their leaves to conserve water supplies. Another leaf feature is that conifer leaves have a waxy outer layer that seals water in.

The organic structure of its leaves aren’t the only winter adaptation available to conifers. The structure of the tree, the wood and the branches, are built for winter survival. All conifers are soft woods, so the branches bend when heavy snow sits on top. The branches point downward for this reason, too—so the snow slides onto the forest floor.

Learn more about the flora and fauna in our watershed on our website!

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