Many people enjoy Autumn as their favorite season of the year. Temperatures are comfortable, most pesky insects are absent, animal migrations are evident, and beautiful Fall colors on the trees and shrubs are stunning. But why do these deciduous plants change color? Consider daylight, temperature, and chemistry.
Spring and summer growth and leaf production are due to photosynthesis, a process where plants use light to synthesize the cell’s chlorophyll into transforming carbon dioxide and water to carbohydrates such as sugars and starch. The cells containing chlorophyll also give the plant its green color. But there are other pigments, besides green, within the leaves all year. Xanthophyll produces orange and yellow colors, anthocyanin develops shades of red. When daylight decreases and temperatures drop in the North, the leaves stop their food-making and the green chlorophyll breaks down, leaving the other pigments to dominate the new Autumn colors.
Soon after these vivid colors appear, the tree develops special cells where leaves are attached. Those cells allow the stems to break away from the tree, due to gravity or the wind, and creates a small leaf scar. Although we may not appreciate bare limbs all winter, heavy snows collected by leaves could cause massive breaking of branches due to the additional weight.
In Southern climates, some broad-leaf trees may keep their leaves and only experience changes during wet and dry seasons. Many stay green all year. And, of course, conifers like spruce, pines and firs, retain their needle-like leaves all year.
Now picture yourself in your favorite, quiet, outdoor setting in the Fall as I read a section from the beautiful writings of Aldo Leopold, found in his book “A Sand County Almanac”. It is titled November – If I Were the Wind.
The wind that makes music in November corn is in a hurry. The stalks hum, the loose husks whisk skyward in half-playful swirls, and the wind hurries on.
In the marsh, long windy waves surge across the grassy sloughs, beat against the far willows. A tree tries to argue, bare limbs waving, but there is no detaining the wind.
On the sandbar there is only wind, and the river sliding seaward. Every wisp of grass is drawing circles on the sand. I wander over the bar to a driftwood log, where I sit and listen to the universal roar, and to the tinkle of wavelets on the shore. The river is lifeless: not a duck, heron, marsh-hawk or gull but has sought refuge from the wind.
Out of the clouds I hear a faint bark, as of a far-away dog. It is strange how the world cocks its ears at that sound, wondering. Soon it is louder: the honk of geese, invisible, but coming on.
The flock emerges from the low clouds, a tattered banner of birds, dipping and rising, blown up and blown down, blown together and blown apart, but advancing, the wind wrestling lovingly with each winnowing wing. When the flock is a blur in the far sky I hear the last honk, sounding taps for summer.
It is warm behind the driftwood now, for the wind has gone with the geese.
So would I—if I were the wind.
Images: Courtesy & Copyright Ron Hellstern, Photographer
Text: Ron Hellstern, Cache Valley Wildlife Association
Autumn Colors, Linda Kervin, Wild About Utah, http://wildaboututah.org/autumn-colors/
Red leaves in autumn: What’s in it for the tree?, Holly Strand, Oct 18, 2012, http://wildaboututah.org/red-leaves-in-autumn-whats-in-it-for-the-tree/
Autumn Leaf Color Change, Linda Kervin, Sept 23, 2010, http://wildaboututah.org/autumn-leaf-color-change/