By Tina Mitchell
Every year, I greet autumn with mixed feelings. The crisp days and cool nights seem to sing after the hot days and much-warmer-than-I’d-like nights of late summer. But these wondrous days get noticeably shorter as each passes. Now that the exhausting tasks of breeding season have ended, the birds have gone silent, and many species have headed out for their wintering grounds. But winter species start to reappear, including the high-flying, raucous flocks of Sandhill Cranes heading over the Sangres to stopover spots in the San Luis Valley. Snow provides an occasional ephemeral dusting on the peaks, offering a lovely contrast to the evergreens below treeline. But I also keep a sharp eye on the weather forecasts, dreading the first meaningful snowfall down here. Actually, snow arrives with its own love/hate relationship for me – but that’s a topic for another time.
One aspect of autumn about which I have no ambivalent feelings whatsoever is the changing foliage colors in the high country. Call me a heretic, but I’m not much of a fan of fall “colors” in the Colorado mountains. I lived my first four decades in the Midwest and the East. Now those areas know how to put on a show of fall colors: brilliant reds, vermilions, crimsons, brazen oranges, persimmons, purples … But I’m sorry. Colorado’s mountain woodlands have fall COLOR – singular, not plural. Yellow. Yellow, yellow, yellow. And more yellow.
Sure, the yellows can be nice, especially in contrast to the dark greens of the evergreens and the pristine blue skies of autumn. One fall, we hiked through a dense aspen grove decked out in full yellow. I felt as if we had stepped inside a sunbeam – not something I’ll forget.
But a little variety would really spice things up a bit.
Why doesn’t Colorado have the stunning tableau of colors found in some other places? Without getting too technical (which I couldn’t do anyway), the answer lies in the biology of the leaves of deciduous trees. Nature’s leaf color palette arises from mainly three types of pigments: chlorophyll, carotenoids, and anthocyanins. In introductory biology, we all met chlorophyll – the substance responsible for the greens in leaves. Critical to the process of photosynthesis, chlorophyll converts carbon dioxide, sunlight,and water into sugars that trees can use for energy. As the days of autumn grow shorter and the nights cool down, photosynthesis slows down and the chlorophyll begins to break down, allowing other colors to show in the leaves. In some trees, carotenoid pigments shine through at this time, producing yellows and oranges. But other tree species manufacture the third color-maker at the end of the growing season – anthocyanin pigments – that produces leaf colors ranging from red to blue. As a side note, it might seem odd that the same pigments can make such different colors. However, anthocyanins are a bit like a litmus test for soil: When the soil tends toward acidic, the anthocyanins turn leaves red; when alkaline, the leaves look more purple or blue. At times, anthocyanins combine with carotenoids for especially vibrant fiery reds, deep oranges and stunning bronzes.
All deciduous trees have both chlorophyll and carotenoids throughout the growing season, but only about 10% of deciduous tree species can create red-to-blue anthocyanins. In the East, though, up to 70% of deciduous trees – e.g., sugar and red maples, red and white oaks – produce them, resulting in the vast expanses and riotous displays of reds, oranges and purples in those areas. In Colorado, the primary deciduous tree of the mountains is the quaking aspen, covering roughly five million acres – nearly one-fifth of the state’s forested lands. And the aspen, alas, does not create any anthocyanins. None. Not even a trace.
I don’t mean to sound totally unappreciative. In some areas, aspens exhibit some nice orange leaves. Right about now, I eagerly await the appearance of a small patch of orange among the aspen stands on a slope of the Sangres framed by our dining room window. Just north of Kenosha Pass, along U.S. 285, we often spot hints of orange among the roadside aspens. Also along 285, the aspens around the Silverheels Ranch area south of Red Hill Pass often display oranges as well. My red-starved eyes home in on any occurrence I can find. Yet even after living in Colorado for more than 20 years, I yearn for the brilliant array of colors from the falls of my younger days. Come each autumn, you’ll find me gazing at the mountains – still, always, longing for, wistfully seeking scarlet.
Tina Mitchell watches nature with her human and canine family from their perch in the piñon/juniper habitat of western Fremont County. When she needs to pay the bills, she shows up as a research psychologist on the University of Colorado Anschutz Medical Campus in Aurora.
