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Cool weather brings early colors

Tom Wiesen
Photo by Tanya WiesenChanged aspen leaves in a mountain stream.
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Walk outside these days and it’s hard not to notice the warm gold, the vibrant yellow, the glowing orange and the brilliant red. Just before the local trees go into winter dormancy, they put on a colorful finale.Autumn is a time of year when the aspen trees stimulate our senses. Suddenly our eyes are attracted to an illuminated stand where we had not noticed aspens in the past. The colors alert our psyche that winter is coming.It is interesting to ponder the nature of aspens – how they always reach for the light and expand their world. Aspens reproduce in a unique fashion. When environmental conditions are just perfect, a seed will fall and, soon after landing, take hold in the soil and up sprouts the first sapling called the mother tree. Aspens are sun-loving, and the mother tree can sense nearby soil that has been warmed by the sun. She sends out underground root runners and then up pops more trees. These trees in turn can sense other nearby sunny spots, send out root runners, and up pops more trees again.

A given aspen stand is connected by a common rootstock, can grow a mile or more across and can contain thousands of trees. It is for this reason that an aspen grove near Crested Butte is considered one of the largest living organisms on earth. Earlier colorsWhen looking at the autumn colors in aspens, notice bright gold leaves next to other trees that are still completely green. This is a time of year when we can detect separate stands. Because each stand is connected by a common rootstock, the leaves within that stand change color simultaneously in the fall.So why do the leaves change color? As we get less sunlight each day the trees go into dormancy as their best way to survive winter. However, this simple answer does not address why it is that the leaves change earlier some years, and later in others. This suggests that there are other environmental factors influencing the growth of the trees, plants and shrubs – such as overall average temperature and moisture.

For instance, with all of the rain we had this summer, I thought that it was going to be a banner wildflower season in the high country. But my personal observation was that it was just an OK wildflower season. What was missing from the equation? It seems to me that there was a lack of typical warm, sunny, cloudless days to promote rampant growth. This summer’s weather was relatively cool and rainy, and it seems to have affected the serviceberry shrubs which turned golden exceptionally early.Staying greenAbout five years ago was the latest fall colors I had ever seen in the Vail Valley and the colors persisted into late October. That summer we steady rain a few times a week, with lots of warm sunny days and a mild autumn. This observation suggests that if environmental conditions favor growth, then the trees hang onto their green leaves longer.The role of the green leaves are to convert energy from the sun by using water and nutrients from the soil and carbon dioxide from the air, and, through photosynthesis, creating carbohydrates and sugars which in turn are fuel for the plant or tree.



As trees sense longer nights – and as growing conditions deteriorate due to colder weather – trees release hormones that cause the draining of chlorophyll and other nutrients from the leaves. When this process is completed, other hormones are released that pinch the nodes where the leaf stems emerge, and causes the leaves to fall with the slightest breeze.It is also interesting to note that there is genetic programming within trees. We often notice the aspens always turn first.There are fascinating mysteries in the natural world. We are especially lucky to be immersed in nature in the Vail Valley. What beauty will tomorrow bring?Tom and Tanya Wiesen are owners of Trailwise Guides; a year-round Vail Valley guide service specializing in private outings for hiking, mountain biking, snowshoeing, cross-county skiing, and wildlife watching. Contact Trailwise at (970) 827-5363.


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