JoAnne Skelly: Amazing evergreen trees

My friend Meri recently sent me a copy of the California Native Plant Society, Tahoe and Sierra Valley Chapter, February and March 2024 newsletter. In it was an informative article by Gale Rankin: The Green Leaves of Winter - Masters of Survival.

The article asked the question: How can evergreen trees (conifers) such as pines, firs, and others stay green all year even in harsh winter areas?

Conifers do not go dormant in winter. Although conifers don’t look like they have leaves, they do. They can be needles as in pines or scales as in junipers and incense cedars. Because nature is so amazing, these plants have developed adaptations to keep their leaves alive in the winter.

Rankin points out that “Drought is one of the major issues (conifer) leaves must deal with in winter.” While there may be snow, the ground is often frozen, limiting water availability. Also, water doesn’t move easily through a plant when it’s cold.

Needles are narrow and scales are compact. These adaptations lower the water demands that otherwise large flat leaves would have. They also shed snow more readily, which helps reduce freeze damage. Conifer leaves usually have a thick waxy coating that also helps reduce water loss.

The pores through which a leaf exchanges gases and water “are sunken deep inside the underside of the needles where they are protected from drying sun, heat and wind.” This means water vapor is less likely to be lost.

But water availability or loss aren’t the only winter challenges for conifers. What happens when ice forms inside the leaf cells? It doesn’t form easily in these plants because evergreen plants’ cells supercool so that the freezing point is much lower than 32 degrees Fahrenheit. They create a kind of antifreeze solution of sugars and proteins within the cells.

An additional adaptation is the plant’s ability to save its chlorophyll from destruction when winter sun provides more energy than the plant can use. Rankin writes, “But plant pigments to the rescue! … [they] intercept the excess light energy, dissipating it as harmless heat.”

You can find more information from Rankin and other California Native Plant Society authors at https://www.cnps.org/chapters/tahoe-sierra-valley.

You might want to consider joining the California Native Plant Society to participate in their wildflower hikes and lectures. The Nevada Native Plant Society can be found at https://www.nvnps.org/. They too are worth joining for great plant hikes and talks.

JoAnne Skelly is Associate Professor & Extension Educator Emerita at University of Nevada Cooperative Extension.