I have crossed the Range of Light, surely the brightest and best of all…
~ John Muir ~
I spent most of my life in the northeastern United States, an area known for its brilliant, eye-popping array of orange, red, yellow, and gold fall foliage. When I moved to coastal Northern California, I entered a world of profound green. The dominant trees in my neighborhood forests are evergreen: redwoods, douglas fir, and bay laurel. They are cooling in summer and deep comfort in winter. But of those, only the laurels contribute color when some of their leaves turn lemon yellow and then copper as the trees do some fall shedding.
Our one deciduous native tree with fall color is the big leaf maple, with leaves that span the length of my hand living up to their name. They also turn a lovely lemon yellow and then pale gold as they fall, giving you a wonderful sense of walking among stars as they cover the ground. This year I asked a friend where one goes to see abundant fall color in California. To the eastern Sierra Nevada, she said. So, carefully choosing a window of time that included color without an early snowstorm, off we went.
The Sierra is a 400-mile mountain range bordering eastern California. It has two distinct personalities: a wetter, greener west side and a drier east side in the rain shadow of the peaks. After 100 years of piping what little water there was to Los Angeles, the area has become even drier. There are vast plains of sagebrush, but in the higher elevations live plenty of evergreens, mostly pines. Wherever there are streams, lakes, or seeps of any kind, there are aspens. And they turn gold.
They aren’t alone. Willows, ferns, grasses, and various shrubs join the array. Some of the latter, especially the dogwood family of trees and shrubs, sport red and burgundy leaves. A few wildflowers were still growing at that altitude. So, it was glorious.
The aspen that dominates upper elevations of the western U.S. is Populus tremuloides, named for the flutter of its leaves in the slightest wind. Clonal, it sends shoots up from spreading roots, which can create vast, long-lived stands of related trees. The 108-acre root structure of one Utah stand is estimated to be 14,000 years old.
Like most magical phenomena, fall color has a chemical explanation. Which, in my book, doesn’t make it any less magical. While the days are long and sunlight plentiful, the all-important photosynthesizing chlorophyll molecules dominate leaf color. These absorb every color wavelength of sunlight except green, which is bounced back to our receptive eyes.
Young spring leaves and the trees that sport them put a lot of energy into creating chlorophyll. Nutrients like phosphorus and nitrogen, along with water and oxygen, are pulled from the soil and up the vascular tissue of the tree to create this crucial-to-all-life compound. If leaves dropped while green, those laboriously acquired nutrients would go to waste and the tree would have to start from scratch every year. Instead, the leaves break down the chlorophyll to store the nutrients in their twigs and branches. This gives chlorophyll production an early season boost the following year. Magic!
As the days shorten and the nights cool, deciduous trees prepare to drop their leaves so they won’t have the hard work of winterizing them. The now broken-down chlorophyll molecules have become transparent, sometimes yellow. Their transparency means we can see the colors of other chemical compounds in the leaf: the yellows and oranges of carotenoids. Some leaves produce special molecules to shade the chlorophyll as it breaks down. This prevents the photons still pouring in from the sun from creating damaging free radicals that interfere with the entire process. The protective molecules — anthocyanins — are red and produce brilliant red and reddish-purple leaves. These polyphenols are the same compounds that create color in flowers and make fruits and vegetables both colorful and good for us.
Watching all this glory is more magic: our eyes. Our color readers are cone-shaped neurons embedded in our retina, six million in each eye. Almost two-thirds of them preferentially read the longer wavelengths of the warm colors: red, orange, yellow. They can distinguish more color variation in those tones than in blue or purple ones, which are transmitted by only 2% of our cones. The remaining third is dedicated to green wavelengths. From those ranges come all the color variations we are sensitive to.
Carotenes and anthocyanins, like their chlorophyll neighbors, absorb and reflect specific light waves. The reflected ones enter our pupils, exciting the cones that are receptive to that wavelength. They send electrical signals via the optic nerve to our brain, which tells us we are looking at yellow, gold, orange, red. Without brains to interpret the messages brought by these wavelengths, there would be no color. Carotenes would still be present in the leaf, absorbing and reflecting sunlight. Cones would even get stimulated. But they only telegraph their excitement. The brain — ours, a hummingbird’s, a butterfly’s — translates the result.
Eyes are so complex that they were the one organ Charles Darwin struggled to fit into his theory of natural selection. How could something so intricate and subtle have worked its way through the often chancy, even clumsy circumstances that drive evolution? He believed it did evolve, but soft tissue seldom leaves a fossil trace to show us how things change. It’s only in this century that scientists have been able to follow the trail through studies of genetic changes and embryonic eye development.
Animal well-being depends on circadian rhythm, so eyes likely developed from early light-sensing organs to help animals adapt to daily and seasonal light changes. Once a rudimentary eye with focusing ability developed, its vast advantages would further drive the selection of ever finer abilities. In the span between 600 million and 500 million years ago — part of the great Cambrian Era explosion of life forms — mammalian eyes became the sensitive and sophisticated image-creating organ we know today.
Eyes, brains, photosynthesis, the emergence of hidden color in the cooling days of autumn. These are all profound, magical mysteries, along with their fascinating scientific explanations. We are both living with such blessings and living through a time of agonizing strife and suffering everywhere we look. When we almost despair of the ability of humanity to behave in ways that foster the health and happiness of the whole.
And yet every single moment we are both surrounded by miracles and are, ourselves, walking, breathing, sensing miracles. Knowing this — living this — can sustain and support us. To trash such gifts and do so much harm in our fight to control and own them is insanity. Our life is the passionate unfolding and the soft falling of a leaf, borne groundward on a breeze. Imagine if we spent that brief span in continual celebration of an Earth of such radical abundance and intricate beauty.
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To love plants is to be in awe of photosynthesis. A crucial, we-wouldn’t-be-here-without-it miracle. Its ramifications are so vast that once it showed up, it dictated all of the evolution that followed.
Reading John Muir’s book of the same title made me want to go and spend the rest of my life looking for Sierra Nevada wildflowers. One summer I got a taste of that wish. I paired the gorgeous, joyful exuberance of his words with some of the beauties he so celebrated.
When I stand on the rocky ledge that is Ring Mountain, the skyscrapers of San Francisco in view, I’m surrounded by a staggering variety of life. There are good reasons for diversity, but the sheer exuberance that has characterized evolution is a wonderful mystery to me.