Our palette of fall!

Gently falling, fading—gone,

Save in grateful eyes.

N.J.B.

We again are losing our summer umbrella of living shingles: the marvelous evolutionary development we call the green plant leaf. In addition to the leaf’s essential process of photosynthesis, they offer shade to soils and organisms in thousands of different ways.

These leaves, though essential to animal life as we know it, are extremely ephemeral. We know that the beautiful leaf colors of fall are related to leaf death and drop, but our sense of loss of this greatest natural form of Earth cover (and perhaps also our dread of the oncoming winter) is dampened by the anticipation of a beautiful leaf show.

Several factors influence fall leaf colors:  increasing night length, decreasing air temperatures, distribution of pigment-making ability in leaves; and, of course, plant genetics.  Genetics determines why leaves or fruits of certain species turn certain colors. But the astronomically-based trend of steadily longer nights as fall progresses (until 22 December) is the unvarying factor in the equation. Color intensity is enhanced by ample rainfall and by steadily falling air temperatures, but is impeded by suddenly freezing temperatures.

The green pigment, chlorophyll, during the growing season, is constantly produced and broken down within leaves, but chlorophyll production slows down and eventually stops as nights lengthen and temperatures drop. And other existing pigments are unmasked.

These unmasked pigments--carotenoid pigments--present along with chlorophyll during the growing season, are the yellow, gold, orange, and brown pigments we see in leaves and in such as corn, buttercups, carrots, daffodils, rutabagas and bananas.

And the anthocyanin pigments, most produced in plants as days shorten and nights lengthen, give their colors to some leaves, and to fruits such as cranberries, red apples, plums, blueberries, grapes, cherries and strawberries. Genetics plays the big role in determining the combination of carotenoid and anthocyanin pigments present in ripe fruits and nuts and in the changing colors of leaves.

Many marvelous processes serve to prepare plants and animals for the cold, and there are many stories to be told about these marvelous processes. But those are tales for another time. The most obvious and beautiful process is that by which trees and shrubs shed their leaves—their most vulnerable parts.

We tend to have tunnel vision when it comes to fall leaf color displays. New England becomes crowded with anticipation, but I’ve seen beautiful displays by maples and other trees in Ohio and Indiana. I recall the beautiful red maples of fall in my Ohio neighbor’s yard. Those maples, however, could not compete with the intensely red, star-shaped fall leaves of the two sweetgum trees in that same yard. I recall two to three boyhood falls in northeast Pottawatomie County that were mildly spectacular. Beauty often is in the eye of the beholder. 

Retiring to the mountains of northern New Mexico meant that my late wife, Imogene, and I would forfeit most of the fall reds of Middle America and the East. But we thrilled in fall to mountainsides sheathed with huge groves of golden aspen. And also to Fremont’s cottonwood, a tree of the SW whose leaves turn a deep golden color. What a treat to stand on a high mountain ridge and see a thick golden strand bending with the Rio Grande for many miles both upstream and down. Reminds me of the old Texas adage: “You dance with who you brung.”