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Changing Leaves, Complicated Feelings

Newts from the Field is a seasonal installment written by Wildlands Ecology Director Shelby Perry, bringing you the wonders of nature from out in the wilderness.

Watching the green drain from the leaves of the lush vegetation of the Northeast has been like watching the summer slip away, and this year more than any other, I will miss summer. Because of the COVID-19 pandemic all of my social activities have been outdoors, and it’s as if the whole rest of the world was forced to adapt to my comfort zone. Everything moved outside, into smaller groups, and with much more open and intentional communication. Friends joined me to watch the sun rise and set, gaze at comets, and immerse ourselves in fields of fireflies. We played croquet and bocce and badminton, circled up around campfires and told stories. We canoed in little wild ponds, swam in sparkling waters, and picnicked under the bluest of skies, and all with some of my dearest friends. My world got smaller, quieter, more local, and more outdoors, and it was everything I needed in these difficult times.

The changing leaves felt like an end to that, so because learning something new always makes me feel better, I have turned to science to help me find my joy in the season again.

We all know the basics: when the days get shorter and the weather colder, the leaves of deciduous plants begin to change colors. Generally, they start out green and change slowly into a color falling into the broad categories of yellow, orange, and red; but occasionally the reds can blend towards purple, and some yellows are more green than others.

These colors all come from pigments in the leaves that absorb some wavelengths of light, and reflect others. The green is from chlorophyll, important for its role in photosynthesis (the process plants use to turn sunlight into energy). Yellow generally comes from pigments called xanthophylls; “xantho” is Greek for “yellow.” These pigments are a type of carotenoid, as are carotenes, which are responsible for the orange colors in leaves. Chlorophyll, xanthophylls, and carotenes are present in leaves all along, and are important in harvesting sunlight for energy production and protecting the leaves from some of the damaging impacts of sunlight. But in summer and spring, the yellow and orange colors are overpowered by the chlorophyll, so we mainly see leaves as green. After the first frost, the tree slows down photosynthesis and stops maintaining its chloroplasts, where chlorophyll is made. As a result, the chlorophyll slowly runs out and yellow and orange pigments begin to show.

The red to purple colors are different though. These come from compounds called anthocyanins, which are secondary metabolites, meaning the plants make them for a purpose that is not part of normal growth, development, or reproduction. These pigments give red and purple vegetables their color and are powerful antioxidants. While all trees produce the pigments described above, only some produce anthocyanins, and only in specific situations. In fruits, they have strong protective qualities that may help the plant defend its reproductive material from certain fungal or biological threats. But a tree in bright fall foliage is about to drop its leaves…so why defend those?

Though still not well understood, the prevailing belief is that this red pigment acts like a powerful sunscreen in the leaves, protecting them from sun damage while the tree works hard to retrieve every last nutrient it can from the leaves before they fall. Sunny days and dry weather, like we’ve seen this year, mean that there is less water in tree sap, and it is therefore more concentrated with sugars. Trees produced anthocyanins prodigiously this year to protect their leaves while trying to glean every last bit of sugar out of them. Rainy and wet years usually mean duller foliage with fewer reds, because the trees don’t need the super-charged sun protection that the red pigments give them.

Armed with a better understanding of the science behind the changing of the leaves, I have decided that this new perspective was just what I needed to process my complicated feelings about this fall. I will not mourn the loss of the leaves as the end of my beautiful summer, but will instead try to glean every last bit of joy out of this wonderful time that I can. And when the leaves fall I, too, will shed the things that no longer serve me, and enter this next season with a new openness. The cold is coming, and I’m going to bundle up, stay outside, and enjoy every moment.