The Daily: 3 August 2024

A Note on Time and Maples

In my part of the world, today is almost exactly an hour shorter than the summer solstice. It took 44 days to drop this hour off the day, much of which time the days hardly changed. But now the changes are becoming more pronounced. It will only take another 22 days to lose the next hour.

This rapid change in day length is what maple trees use to judge when to go dormant. Maples, like most trees, somehow count both the hours of darkness each day and the number of days with long nights. When we begin to lose several minutes off of each day, the maples begin to cut nutrient supply to their chloroplasts and these tiny organelles die. When that happens, the leaf stops photosynthesizing. So then the tree judges that leaf useless and cuts off the nutrient supply to the whole leaf. This lag time between shutting down photosynthesis and cutting off the leaf means that, for a brief time, we get to see living leaves that are not photosynthesizing. We get to see them in the colors that their tissues reflect when they are not absorbing all the light except the green bits. We get to see them in their natural colors. This is what makes the autumn tapestry.

Most trees turn some variety of yellow, or rather yellow is the light they reflect back to our eyes when not photosynthesizing. Yellow, the color of carotenoids, is a very common color for dormant plant tissues. We know that most dormant leaves are rich in these compounds because yellowish-brown is the color we see when a leaf is ill. Our houseplants turn yellow because the plant has shut down photosynthesis either near the stress or just at the edges of leaves, so that the plant can withdraw its nutrient flow into a smaller area. It is curling inward on itself, just like we do when we feel stressed, and indeed, the yellowed leaves do curl. I feel that this reveals the unfolding and folding of growth and decay. A new organism unfolds, uncurls, opens up and grows wide. An old organism folds, curls, contracts into a tiny remnant of itself. When nerds like me translate this opening and closing over time into an equation and plot its points on a graph, the whole process looks like a wave. Or a circle…

This is the point in the circle when maples are beginning to show their true colors, and maples have different chemistry than many trees. Few maple species turn yellow. When maples go dormant, they turn the astonishing hues of anthocyanins (which, for the record, are extremely good for our body tissues). These pigments reflect red, but they are sensitive to cell sap acidity. When exposed to low pH, acidic surroundings, anthocyanins appear the bright red of apples. When sap pH is higher, more alkaline, they look purple to our eyes. Anthocyanins are responsible for the deep violet of grapes and the purples of figs and eggplant. When mixed with carotenoids, they turn plant tissues pumpkin orange.

A further fun trait of anthocyanins is that they only form when there is high sugar content in the cell sap, and this sugar must come from photosynthesis, from sunlight. Think about a mottled red and green variety of apple like macouns. Often one side will be a brighter red than the other. This is because one part of the apple is exposed to more sunlight and is richer is sugary cell sap. The shadier side will be more greenish. It will be more tart because there is less sugar. A really good macoun will be a balance of tart and sweet. I like them with a bit more green than red.

So back to maples. With their broad leaves and sugary sap, they build lots of anthocyanins into their leaf tissues. When those anthocyanins are exposed to high soil pH (alkaline soil), they turn purply. Japanese maples, rich in anthocyanins, grown in neutral to alkaline soils always look more purple than green to our eyes. Japanese maples in the acidic soils of New England, are autumnal red virtually the whole growing season, while swamp maples (acer rubrum) turn nearly fluorescent red in the fall. Boggy places, with their acidic soils and bright sunshine (because few trees can live in watery soil), are bordered in the brightest colors.

Vermont’s sugar maples grow in neutral to acidic soil and their large leaves are sugar factories. Over time, maples — ever the aggressive seeders whose saplings can grow in near darkness until a fallen tree opens up the canopy — will take over large swathes of the forest. Maples are also found with the opportunistic poplar family, which includes birches, beeches and aspens. These trees turn sunflower gold in the autumn. So in the fall, Vermont erupts into flaming color.

But we are not there yet. Today, the maples are just to the point in their counting of the hours that they are starting to consider winter dormancy. There are a few leaves here and there, mostly near the top of the trees, that are changing hue, but it will be some weeks before the mountains are lit up in full fiery color. In fact, it will probably happen about six weeks from now. Vermont’s maples are consistent time-keepers, and they seem to believe that the equinox is bedtime. All their chloroplasts are shut down; the leaves will follow shortly. We usually have a week or two around the equinox to enjoy this spectacle… and then the mountains turn wood-brown.

Until the snow falls…

Because time is a circle of opening and closing, unfolding and folding, growth and the respite of decay. And, right now, we are rapidly arcing around the transition from one to the other.

---

©Elizabeth Anker 2024