Maple leaf early stages of color change.
How beautifully leaves grow old. How full of light and color are their last days.
-George Burns
We’re in the midst of an Indian summer with highs of 80℉! The skies are mostly blue and there is only a slight breeze. This, of course, means Wado and I are walking in the late morning, but I kinda like to walk then anyway. We’re done by about noon and that leaves the rest of the day for other stuff.
Before this, there were some low temperatures, down to nearly freezing, that must have triggered the maples and other trees to start changing colors because there are many more reds, yellows and tans out here. The rail-trail tunnel is still green, and the mighty oaks are not yet all tan, but, in the places where birch trees dominate, leaves are falling a dozen at a time. A light breeze kicks up and it’s almost like it’s snowing yellow leaves. The birch part of the trail has not yet turned into the yellow brick road, but that’s not far away. With these high temperatures, were I a tree, I’d be kinda confused about now, but the earlier freezing temps seem to have acted like a switch, because I don’t see the rate of color change ebbing even a little.
I like to look carefully at the leaves as their colors change. I walk off to the side of the trail and stare at this leaf and that, still hanging on its branch, or bend over and gaze at some of those that are on the ground. I particularly like the brilliantly contrasting patterns created at various points of the color development. Mother Nature can be quite beautiful.
Leaves are the factories of life – creating living tissue from sunlight, carbon dioxide and nutrients from the soil. Chlorophyl is the photosynthetic pigment that makes this happen. It is not the only photosynthetic pigment, but is the most efficient one. It absorbs light in the red and blue part of the spectrum and reflects green. That’s why leaves are green. Nature may have evolved this compound, it was at least serendipitous, because the peak of the solar output of visible light is in the yellow-green. By being able to absorb the red and blue part of the spectrum, chlorophyl can use a good portion of the light available.
If trees held onto their leaves year-round, the cold temperatures of winter would cause their living cells to form ice crystals. That would destroy the cells and the trees would lose all the nutrients they contained. Instead, trees have evolved the ability to resorb those nutrients, let the leaf die, and regrow new leaves in the spring. Most trees, but not all, then shed their leaves for the winter. Those that don’t, marcescent oaks (the oaks that hold onto their dead leaves through winter), for example, shed them in the spring when they grow new leaves.
In the process of resorbing nutrients, chlorophyl is broken down and the pigments that are left behind have different colors than green. Many trees have yellow and tan pigments, some have red. This resorption doesn’t happen uniformly all at once, though. The nutrients flow back into the tree through veins in the leaves. This happens by diffusion, since there is no pump in the leaves to make that happen. That means that at the beginning of the process, the veins and the regions right around them, are a pale green-yellow (because the chlorophyl there has been broken down and resorbed) while the lamina (the are of the leaf between the veins) is still very green. The result is a pretty pattern in shades of green that isn’t there during the height of summer.
Toward the end of the process, the nutrients have mostly been resorbed from the lamina and only the areas around the veins retain that yellow green tint. In red maples, and some other trees, what’s left is red and that makes, in my estimation, the most beautiful patterns of contrasting colors — red with streaks of light green and yellow.
That’s not the end of the process, though. Eventually, if the leaf stays attached to the tree, it will have only the dead pigments left (the red maple leaf will be all red). So, usually, you have to look for the leaves at the right time while they’re still on the tree. Sometimes, you can see the almost-dead leaves on the ground, where the process of resorption is frozen, because they have been shed early. Wherever you find them, they are a true work of art.
Not all leaves die in the winter. English ivy, for example, stays green throughout the winter. I’ve seen ivy leaves stubbornly dark green when the temperature was as low as -32℉. They have evolved a waxy coating on their leaves that protects them from dying and they survive all year long. Pine needles, a kind of specialized leaf, stay green too, have a waxy coat and remain attached to their trees. Some, by no means all, are shed in the late summer and early fall, but not because of the coming cold. They have evolved a different strategy of survival, but that’s a different story. Mother nature doesn’t evolve just one mechanism for survival, you know.
I would guess the beauty of a nearly dead red maple leaf is lost on Waldo – dogs can’t see red. But then, dogs have their noses and, I suppose, that comes with its own appreciation of fall beauty. But I can revel in the rich colorful, although temporary, beauty of an early fall day.
And I do.
Maple leaf late stage, but not complete, color change.