We often associate winter with the lack of color. The leaves have fallen, with only their decaying remnants to remind us of their former glory. Now all we can do is await the new growth of spring, with the emergence of fresh buds and the unfurling of leaves.
But even in the dead of winter, life endures. A walk through the woods behind my house reveals not only an abundance of mosses and ferns, but also ivy, holly and laurel as well as massive firs and cedar trees. Many plants have adapted means to defy the conventional ways, and provide green leaves throughout the year.
Deciduous plants cut off their connections to the leaves when it turns cold. They stop the process of photosynthesis in order to save energy for the winter. These plants retain stored food, usually in their root systems. During the winter, deciduous plants go dormant and most cellular activity stops.
But there are plants that have chosen a different path. They have learned ways to deal with the cold temperatures and reduced light, and still continue to produce energy.
Several simple but elegant adaptations set the evergreens apart from the leaf losers.
For example, the pines and firs resort to a change in leaf shape to aid their objective. With hair-like needles, snow tends to slide off without sticking. This does two things. First it prevents the modified leaves from freezing. It also keeps the surface of the needles free to receive the suns rays. The waxy coating on the needles also has a duel purpose. It gives the needles a slippery surface to allow the snow to slip off them, and it locks in the precious moisture the tree needs to survive.
Many evergreen plants including holly and laurel have waxy leaves. Holly also comes equipped with spiny leaf margins to keep winter grazers away. Many year round photosynthesizers have come up with ways to deal with the appetites of the local fauna that would otherwise decimated these plants once their regular food sources have disappeared.
Chlorophyll molecules, which give leaves their green color, absorb sunlight and use it to convert carbon dioxide and water to simple sugars. This is the essence of photosynthesis.
In evergreen plants, photosynthesis and respiration slow down during the winter, but do not stop completely.
As the days grow shorter, and the sun hangs lower in the sky, temperatures drop. During this time, photosynthesizing requires extra energy. Molecules just can’t move as fast in this frigid climate. A reduction of photosynthesis can also mean a smaller amount of chlorophyll, which in turn can lead to less green in the leaves, and this allows us the see the other colors that were hidden in the leaves the whole time.
This was bared out the other day when I took a stroll through the woods. I happened across a single Western Sword Fern (Polystichum munitum) that was shockingly different than the rest. And, although the area I walked was filled with sword ferns, none of the others even had a hint of the coloration that this one displayed. I didn’t ask myself why this fern was arrayed in such color, but I did wonder why only this one had made the change.
Not to be outdone, a nearby ivy leaf had to show its colors as well.