By Boak Wiesner
Fall is arriving rapidly. We’ll see some 80’s for highs this week as well as some 30’s for lows. Are these wild fluctuations typical or the norm? Thus, patterns and perturbations were on my mind.
Even as I arrived, a perfect example of my theme set itself before me. The colors of leaves are beginning to stand out. Sugar maples, given the fact that they produce an abundance of sucrose in their leaves, hence their name, show some of the most vivid red coloration of tree leaves in the fall. Notice how the color is mostly on the sunny south side; the amount of sugar produced is determined by how intense the sunlight is. Since it is out of sugars that the pigment anthocyanin is produced, the more sugar, the more color. Fruits, since they contain a lot of sugar, as plants evolved to get their seeds dispersed by wrapping them in delicious sugary fruits, show a lot of red or purple anthocyanins. Think of a plum.
So the overall pattern is that leaves show colors other than green in the fall, but on each individual tree, where the sunlight strikes it perturbs this into a spectrum of coloration.
The sun itself shows patterns and perturbations. The face of the sun these days shows just one measly sunspot, even though the historical record of 11- and 22-year cycles indicates that they should be peaking in number around this year. What happens when there’s a lull in the solar cycle? Colder temperatures. So if that relationship is maintained, we could see a colder winter than what we might have. Maybe the sun is just a year or two late; maybe there’s a major calming of the sun’s interior. The last big one occurred in the late 1600’s and is called the Maunder Minimum after the British astronomer. It coincided with the “Little Ice Age”, the effects of which are well-depicted in art of that period.
Back to the trees. Ashes tend to show the yellow xanthophyll as they produce much less sugar than the maples, and the birches also show intense yellow colors. Still, though, there’s more vivid color in the areas where the sun shines on them more intensely, whether they’re exposed on a hillside, or have a patch of sun come through where the road passes by.
The stalks of Big Bluestem show vivid colors. Sometimes I wonder if Louis Gerard, whose name is referred to in the species epithet for Big Bluestem, was somehow colorblind, as that stem is most certainly not blue. But would “Big Magenta-stem” fall as trippingly off the tongue?
Boak Wiesner is a Minnesota Naturalist volunteer.