Tales from the Field: The Fall Phenomenon

October 22, 2015

Fall leaf
Fall leaf at White Pines Nature Preserve, photo by Sonke Johnsen

Every year a natural phenomenon occurs across the country. This phenomenon brings great beauty throughout the landscape and clogs the roads of Hendersonville and other mountain towns every year as thousands travel to witness it. When the leaves begin to turn colors in the fall, life seems to slow down as folks enjoy the natural splendor that unfolds.

As a native of the mountains of Western NC, I consider myself a “closet leaf-looker.” What do I mean by that? Well, I mean that as a local, I enjoyed the beautiful colors every fall without traveling 15 miles an hour below the speed limit like most seasonal tourists. Joking aside, fall brings the most epic beauty to the landscape, a splendor that I didn’t fully appreciate until I moved away from the mountains, and returned for a weekend about this time a few years back. I write this blog a week after returning to the mountains again during the peak of the colors at Blowing Rock, NC. These dazzling colors were an amazing backdrop during a fantastic trip to Tweetsie Railroad.

Tweetsie Railroad
Tweetsie Railroad in the Fall, photo by Kyle Obermiller

Growing up, the fall colors were just one of the weird things nature does. Some years were amazing, some years were wiped out by hurricanes, or most of the time a huge rain would take the leaves away and traffic and life would return to normal again. Until curiosity finally led me to seek answers to my questions, I figured leaves died and the wind blew them off; and that’s just what nature does. As usual, I was wrong in my simple assumptions.

The correct reason is a lesson in survival, and you might say it’s something “cool” to learn.  As it normally does, science becomes amazing when you look at questions on a microscopic level. In deciduous trees (trees that drop their leaves seasonally), cool weather signals a chemical reaction to stop photosynthesis and reduce production of carbs and sugars (plant food). The signal also begins the breakdown of chlorophyll, allowing other pigments like xanthophylls (yellow), carotenoids (orange), and anthocyanins (purple) in the leaves to become more prominent – hence, fall colors! At the same time, the place where the leaves connect to the stem begins producing abscission cells, a thin, bumpy line of cells. These cells seal off the connection between the leaf and the stem and begin to push the leaf away from the stem. Essentially, the tree is forcing the leaves to drop.

Abcission cells
The scissor cells are stained red and mark the boundary between the branch (left) and the leaf stalk.
University of Wisconsin Plant Image Teaching Collection

In my mind, the tree forcing its leaves to drop is like a restaurant firing all their staff at once. At first thought, it doesn’t make sense, but further investigation gives you an answer. Leaves contain water to enable photosynthesis, and during winter freezes, the water would expand and rupture the cells rendering the leaf useless. Rather than growing new leaves after every freeze, deciduous trees lose their leaves when colder temperatures rise to avoid wasting valuable energy that would otherwise be spent on many cycles of leaf production annually.

I think it’s pretty cool, and in a few weeks it will be a great reason to get out locally and enjoy tour area’s colors. I suggest heading out to the Peak’s Loop at Horton Grove Nature Preserve, or strolling along the high bluffs at Swift Creek Bluffs Nature Preserve in Cary. There are plenty of opportunities to relax and enjoy the beauty and views open space has to offer here in the Triangle. With the current weather sunny and cool, there’s no better time to get out and enjoy nature! This is The Dirt – Tales from the Field asking you to get outside and enjoy fall! Feel free to send your stories, questions, or comments my way: [email protected].


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