Thursday, February 4, 2010

Winter Cedars

It’s been a rather cold, windy winter so far and the Eastern Red Cedars are beginning to show some signs of stress. Although they are considered evergreens, they do display annual color shifts as a result of local environmental conditions. Air temperature, wind, precipitation, soil moisture and soil type all influence how an individual cedar is going to react. Since some of these factors can vary considerably over short distances, the visual signs of stress might differ drastically between one tree and the next.

The green color in leaves is chlorophyll, a necessary component for photosynthesis. Chlorophyll is constantly being lost and replaced as long as conditions remain favorable. Cold temperatures and shorter day length in winter will slow photosynthesis, but the balance between chlorophyll loss and replacement can still be maintained. The factor that seems most likely to break the cycle, is desiccation of the needles. Without a suitable amount of water, chlorophyll production stops and the needles gradually show less green color as the existing chlorophyll is lost and not replaced.

Small cedars typically show these effects each year. The tree stops taking in moisture when the ground freezes around the small, shallow root system. For the tree, this is the equivalent to experiencing a drought, but the cedar is extremely drought tolerant and can normally survive this type of punishment.

Larger trees take longer to show drought effects. Large trees are still shallow rooted, but it takes longer for the ground to freeze to a deep enough level to stop water intake. If you add the drying effects of the wind, the tree loses water faster than it can be replaced. Trees that stand in the open will show a change of color much sooner than those in more protected areas.

Here’s the color difference between a protected branch on the left and an exposed branch. The protected branch is as green as it was during the summer. The exposed branch has lost a large amount of chlorophyll, but it is still perfectly healthy and will green up again once conditions improve in the spring.

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